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HomeMy WebLinkAboutSWP272271(3) * AGRA AGRA Earth& Environmental, Inc. Earth & Environmental 11335 NE 122nd Way Suite 100 Kirkland, Washington U.S.A. 98034-6918 ' Tel (206)820-4669 15 May 1996 Fax(206)821-3914 1 1-1 0496-01 City of Renton ' Planning/Building/Public Works Department Municipal Building 200 Mill Avenue South Renton, Washington 98055 Attention: Mr. Ronald J. Straka, P.E. ' Engineering Supervisor Subject: Subsurface Exploration and Geotechnical Engineering Study High Avenue South Outfall 525 High Avenue South Renton, Washington Gentlemen: ' This report presents the results of our subsurface exploration and geotechnical engineering study for the above referenced project. The purpose of this study was to interpret general surface and subsurface site conditions from which we could formulate a summary discussion ' regarding general site stability, temporary open cut slope and shoring considerations, and soil design parameters for the excavation and replacement of the upslope storm water catch basin and piping. Recommendations regarding support for the proposed High Density Polyethylene (HDPE) piping down the slope to the concrete energy dissipator/diffusion structure are also discussed. Our scope of services consisted of a visual site reconnaissance, subsurface exploration, laboratory testing, geotechnical analysis, and preparation of this report. Our work has been performed in accordance with our scope of geotechnical services dated 14 November 1995 and our on-call consultant contract with the City of Renton. Authorization to proceed with this study was granted by the City of Renton on 4 January 1996. This report has been prepared ' for the exclusive use of the City of Renton, and their agents for specific application to this project in accordance with generally accepted geotechnical engineering practices. ' SITE AND PROJECT DESCRIPTION The storm drain outfall is located at the north end of High Avenue South, northeast of a residence located at 525 High Avenue South in Renton, Washington. The storm drain outfall Engineering& Environmental Services ' City of Renton 1 1-1 0496-01 15 May 1996 Page 2 is a 12-inch diameter corrugated metal pipe (CMP) which serves as the discharge for the ' collected upland surface water. The nearest catch basin for the CMP is approximately 75 feet south of the top of slope and 90 feet south of the outfall. The storm water discharges from the pipe near the top of the slope and follows a drainage channel steeply downslope. ' We performed a preliminary geotechnical memorandum in late August 1995 to assess impacts to the storm drain line and future slope stability after a landslide occurred following heavy rains on 16 August 1995. Additional observations on 9 October 1995 disclosed substantial channel cutting and loss of bank soils in the discharge area compared to our 31 August 1995 geologic reconnaissance. The City of Renton performed temporary erosion control measures in mid October 1995 including a tightline extension to the outfall pipe, and placement of geotextile fabric atop the upper exposed slope soils and below the tightline pipe. ' We understand the City of Renton plans to reconstruct the existing outfall with a HDPE tightline. A new upslope catch basin inlet manhole will replace the existing catch basin and serve as the start of the HDPE tightline. The HDPE tightline will exit the catch basin at a depth of approximately 10 to 15 feet below the top of slope and then continue atop the surface of the drainage channel to its terminus at a new downslope energy dissipator/diffusion structure. In the event of any changes in the nature or design of this project, the conclusions and recommendations contained in this study should be reviewed and modified, as necessary, to ' reflect the changes. SITE CONDITIONS ' The site conditions were evaluated for this study in August and October 1995, and January 1996. The surface and subsurface conditions are described below, while the exploration procedures and interpretive logs of the explorations are presented in Appendix A. The general project vicinity is shown on the Location Map, Figure 1. The approximate locations of the explorations are indicated on the Site and Exploration Plan, Figures 2 and 4. Laboratory procedures and test results are presented in Appendix B and on the exploration logs, where ' appropriate. Surface Conditions ' The site is located at the north end of High Avenue South, northeast of the residence located at 525 High Avenue South, in Renton, Washington. The upslope area includes a catch basin within the asphalt roadway/driveway, a gravel parking area, a landscaping berm including beauty bark and plantings and grass covered areas. The eroded slope area adjacent to the existing outfall pipe where landsliding has occurred is approximately 35 to 40 feet in width and 25 to 30 feet in height. In mid October 1995, the City of Renton extended the outfall pipe further downslope and placed geotextile fabric atop the upper exposed slope and below the tightline pipe extension to reduce further erosion. ' ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 3 The drainage channel below the outfall was surficially covered with quarry spall rock (4- to 8- inch) in the splash area and a limited area further downslope. The slopes adjacent to the drainage channel were generally covered with surface brush, blackberries, and small alder and maple trees. The trees on the slope have been regularly topped for the downtown view to the northwest. A 10- to 20-foot high pile of accumulated trees, root mass, brush, soil, quarry spall rock, and debris including concrete and CMP is located at the base of the upper slope within the drainage channel. The debris pile is on the order of 60 feet in length. A smaller debris pile consisting of finer debris, wood, and soil is located downslope of the large debris dam. An alluvial fan ' type soil deposit is located below the debris piles in the area of the proposed energy dissipator/diffusion structure. The topography becomes less severe in this area where soil is deposited during outfall runoff. ' Further downstream, the drainage channel cuts through waste piles of coal, siltstone, and ' sandstone to pond at the base of the slope in the proposed City of Renton park site. During a heavy rain event, we observed that the runoff drained to a catch basin at the northwest area of the proposed park. Subsurface Conditions To assess subsurface conditions we performed an exploration program including one test boring at the top of the slope and five trackhoe excavated test pits in the area of the proposed energy dissipator/diffusion structure near the bottom of the slope. ' The test boring disclosed approximately 4.5 feet of fill soils consisting of a very loose to loose silty gravelly sand with some organics atop a recessional deposit consisting of loose sand with trace gravel, silt and organics. At a depth of approximately 10.5 feet to 31 feet, we encountered a very stiff to hard sandy silt with some gravel and interbedded sand. A dense sand with trace gravel and silt was encountered at approximately 31 feet in depth and graded to gravelly at 36 feet to the total depth of the boring at 39 feet. Below the recessional ' deposits at 10.5 feet, the soils are classified as undifferentiated deposits which include three or more glacial till sheets, glaciofluvial sand and gravel, glaciolacustrine clay and sand, and non- glacial sand, clay, and thin peat. ' The trackhoe excavated test pits in the area of the proposed energy dissipator/diffusion ' structure disclosed approximately 8 to 10 feet of fill and/or colluvium consisting of a loose, silty sand to sandy silt with some gravel to gravelly and coal, wood, and brick fragments. Native, medium dense silty sand with some gravel was typically encountered below the upper loose ' soils in the test pits. Moderate to severe caving of the test pit walls was observed within the fill soils. Test pit TP-4 encountered wood timbers within the fill soils. It would appear that the fill and/or colluvium encountered in the test pits is related to mining of resources of coal and ' siltstone from the site area. A brick manufacturing company existed downslope at the ,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 4 proposed park site, which mined the siltstone (shale) for brick manufacturing. As mining of resources was conducted, the spoils remained at the base of the slope. Though our test pit explorations were limited, areas of mounded spoils, and disturbance to the area was observed across the lower slope areas. In addition, downslope movement of surficial soils including slumps (colluvium) were observed in the lower slope area of the project site. Groundwater was not observed in our test boring at the top of the slope, but was observed as ' moderate to rapid seepage at depths ranging from about 1.5 to 10 feet in all five test pits at the bottom of the slope. It should be noted that seepage from precipitation may at times become "perched" within the fill and/or atop the dense silty sands and hard sandy silts of the ' undifferentiated deposits in the upper slope area. If perched water is encountered, the proposed outfall design improvements should not require further modification. Please refer to our recommendations in the site preparation, drainage and slope considerations sections of this ' report as they relate to groundwater seepage. GEOLOGIC RECONNAISSANCE We performed a geologic reconnaissance of the drainage channel slope for our previous study on 31 August 1995. For this study, we performed a ground surface geologic profile of the slope and incorporated our test boring advanced at the top of the slope. We visually observed site conditions and channel soil contacts during our site reconnaissance on 22 January 1996. The topographic information, based on a City of Renton supplied topographic plan, shows a top ' of slope elevation of approximately 326 feet and 55 feet at the bottom of the slope. The toe of the accumulated upslope debris, spalls, etc. is approximately elevation 160 feet. The proposed energy dissipator manhole structure will be at approximately elevation 140 feet. ' Presented below is a summary description of the channel soil contacts observed during our site reconnaissance. The existing slope profile and soil contacts are shown on Figure 3, Ground Surface Geologic Profile. Our test boring generally correlated with the exposed soil contacts in the drainage channel. Approximately 5 to 8 feet of very loose, silty, gravelly sand fill was observed atop 5 to 6 feet ' of loose sand with trace gravel. This native sand is mapped as recessional stratified drift, Qit, kame terrace deposits. The Renton Quadrangle Geologic Map, 1965, describes the Kame terrace deposits as sand and pebble to cobble gravel in scattered terraces whose surfaces ' locally are deformed by extensive collapse. The fill and recessional soils have formed a near vertical slope (.5 Horizontal:1 Vertical) from the top of slope to approximately 5 feet below the outfall in the drainage channel. Below the recessional deposits and approximately 5 feet vertically below the outfall pipe, we observed a 15-foot near vertical slope of glacially consolidated, very stiff to hard sandy silt with some gravel, mapped as Qu, undifferentiated ' deposits. The undifferentiated deposits include three or more till sheets, glaciofluvial sand and gravel, glaciolacustrine clay and sand, and non-glacial sand, clay, and thin peat. ,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 5 We observed Qu deposits of interbedded silty sands, sandy silts, and gravelly sands in our test ' boring and along the drainage channel and banks for approximately 60 feet on a slope on the order of 1 H:1 V (Horizontal:Vertical). Our test boring encountered a sand interbed of the Qu deposit from approximately 31 feet to the boring bottom depth of 39 feet. Though not ' encountered in the test boring, the sandstone (which is mapped as the Renton Formation (Tr)) was observed in the drainage channel approximately 60 feet downslope from the base of the near vertical slope below the outfall. ' A layer of quarry spall rock (4 to 8 inches in size) and geotextile fabric covers the upper drainage channel below the outfall to approximately the sandstone contact. The Renton Formation consists of arkosic sandstone, mudstone, shale, and coal beds. This formation is characterized by numerous faults of small displacement, wavy bedding, and a thickness of approximately 2,500 feet. The coal and shale (siltstone) from this formation was mined extensively in Renton, including beneath the project area. The observed upper sandstone forms a 1 H:1 V slope (similar to the Qu deposits) for approximately 15 feet and then drops vertically ' approximately 20 feet. The sandstone in the drainage channel has formed steps with interbedded coal and siltstone for approximately 100 feet. The steps form an overall slope on the order of 1 .25H:1 V. A 10- to 20-foot high pile of accumulated trees, root mass, brush, soil, quarry spall rock, and debris including concrete and CMP is located at the base of the upper slope at approximately elevation 165 feet. The debris pile is on the order of 60 feet in length. A smaller debris pile consisting of finer debris, wood, and soil is located downslope of the large debris dam. A siltstone horizon of the Renton Formation was observed beneath the debris piles. Further downslope, we observed interbedded sandstone, siltstone, and coal along the drainage channel. In the area of the proposed energy dissipator manhole structure, an alluvial fan type soil deposit is located where the topography becomes less severe. The runoff channel in this area deposits sediment rather than downcutting a deeper channel. Downslope movement of surficial soils including slumps and/or colluvium are evident in the lower areas of the channel. The lower ' areas also contain fill, as observed in our test pits, which relate to the mining of the siltstone and coal from the area. ' Groundwater seepage from the upper slope was not evident during our site reconnaissance. We observed surficial seepage in the area of the test pits in the lower slope area. Refer to the ' test pit logs for noted surficial seepage and depths of observed seepage. CONCLUSIONS AND RECOMMENDATIONS Development plans call for removal of the existing catch basin structure on High Avenue South and the approximately 90 feet of existing corrugated metal pipe (CMP) to the north. Replacement with a new concrete manhole and 12-inch diameter high density polyethylene (HDPE) pipe is planned. The HDPE pipe will tightline the storm water down the surface of the ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 6 slope to an energy dissipator/diffusion structure near the base of the slope. The proposed energy dissipator/diffusion structure will be a 54 to 72 inch diameter partially buried manhole structure where the HDPE tightline will enter near the ground surface. The outlet pipe from the structure will be higher than the inlet to dissipate the energy of the storm water. Improvements to the storm water outfall are necessary to lessen the erosion and downcutting of the drainage channel in the upper slope area and possible damage to the existing CMP ' outfall. Site Preparation and Structural Fill ' Based on our test boring, the top of slope area at the boring location consists of approximately 4.5 feet of very loose to loose silty, gravelly sand fill atop approximately 6 feet of loose sand (recessional deposits). At 10.5 feet in depth to approximately 31 feet, a very stiff to hard ' sandy silt interbedded with sand was encountered. A majority of the excavation for the new upper catch basin manhole and HDPE pipe, planned at a depth of approximately 10 to 15 feet ' below existing grade, will encounter the existing fill soils, loose recessional sands, and possibly the very stiff to hard sandy silts. The exposed subgrade surface for the catch basin structure should be free of loose/disturbed soil or standing water and compacted such that an in-place soil density of at least 90 percent is achieved to a depth of 12 inches, using the ASTM:D-1557 modified Proctor maximum dry density. We recommend a bedding material for the catch basin suitable for rigid pipe consisting of crushed, partially crushed, or naturally occurring granular material free from wood waste and organic material and having a maximum dimension of 1 inch. The bedding material should conform to the gradation described in Section 9-03.15 of the 1994 WSDOT/APWA Standard Specifications. If any organic or unsuitable soils are encountered at the proposed pipeline subgrade, overexcavation to expose suitable competent material would be necessary. Backfill should consist of compacted Class A, Class B, or Class C Foundation Material as described in Sections 9-03.17 and 9-03.18 of WSDOT/APWA 1 Standard Specifications. Controlled Density Fill (CDF) or lean concrete may be used as an alternate foundation and backfill material. According to manufacturer specifications, no bedding material is required below HDPE pipe. ' To prevent migration of water within the bedding material or backfill and potential of sloughing of the slope during compaction, use of CDF within 30 feet behind the slope is recommended ' in lieu of a permeable granular bedding material. Alternatively, the use of low permeability pipe collars, such as CDF, clay/bentonite or concrete collars/check dams could be installed at several locations along the buried HDPE tightline. The pipe collar should fully envelope the pipe and extend a minimum of 1-foot below the base of the trench and 1 foot above the top of the pipe bedding. We anticipate that pipe collars on the order of 3 to 4 feet in length should be adequate. As previously mentioned, roughly 10 feet of loose fill with debris was encountered at the proposed downslope energy dissipator location. It will likely not be practical to overexcavate ' ,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 7 and replace all the existing fill beneath the energy dissipator structure. Therefore, it is our ' opinion that overexcavation of 3 feet of unsuitable soils be performed below the structure. Due to the presence of groundwater and poor ground conditions, we recommend that quarry spalls be used as foundation backfill material for the 3 feet under the structure. The quarry spalls ' should be firmly seated into the underlying ground using the bucket of the excavator. We recommend that the quarry spall foundation mat extend laterally at least 2 feet beyond all sides of the energy dissipator structure. A limited length, on the order of 30 to 40 feet of HDPE pipe will be buried in the downslope pipe trench as it connects to the outlet structure. The depth of burial will vary from ' approximately 1 to 4 feet and bedding material is not required below the HDPE pipe. The suitability of soils for structural fill use depends primarily on the gradation and moisture ' content of the soil when it is placed. Soil to be used as structural fill should be free of organics and other deleterious material. As the amount of fines (that portion passing the U.S. No. 200 Sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and ' adequate compaction becomes more difficult or impossible to achieve. Soil containing more than about 5 percent fines by weight usually cannot be compacted to a firm, non-yielding conditions when the moisture content is more than about 2 percent above optimum. We anticipate that the on-site soils for the High Avenue work that would be available for fill as ' a result of trench excavation would primarily be a silty gravelly sand with some organics (old fill) and a sand with trace gravel, silt and organics. The soils disclosed in the test pits near the proposed energy dissipator location consist of loose silty sand with some gravel, wood, coal and organics (fill and/or colluvium) to a depth of approximately 10 feet. It should be realized that the on-site soils are moisture-sensitive and may be difficult or impossible to use as structural fill during wet weather or under wet site conditions. If rain were to occur while silty soils are exposed, or during their placement, the exposed material should be allowed to sufficiently dry prior to additional filling, as necessary to facilitate compaction. It may be necessary to scarify the upper layer, allow it to dry, and recompact prior to additional filling. ' It may be necessary to overexcavate and remove wet soils if it is not practical to dry and recompact them. Select "clean" granular soils would then be required for structural fill use. ' Select imported fill should consist of "clean" free draining, well graded sand and gravel as specified in WSDOT/APWA Section 9-03.19, "Bank Run Gravel for Trench Backfill". Imported fill soils should contain no more than 5 percent fines by weight passing through the U.S. No. 200 Sieve when measured against the minus No. 4 fraction. Material of this type may be successfully placed and compacted under a wider variety of weather conditions. Soils used for structural fill should have no particles greater than 2% inches in maximum dimension and be free of organics and other deleterious materials. Structural fill should be placed over a properly prepared subgrade, as discussed above. Structural fill should be placed in 8-inch maximum PAGRA Earth & Environmental r City of Renton 1 1-1 0496-01 15 May 1996 Page 8 1 loose lifts. Each lift should be compacted to at least 90 percent of the laboratory Proctor ' maximum dry density, using ASTM:D-1557 as the standard. Drainage Considerations ' Based on our explorations, groundwater was not encountered in our test boring advanced at the top of slope area, but was encountered in all of the test pits at the base of slope at depths from 0 to 10 feet. The excavations for the proposed structures and pipeline should be ' dewatered as needed prior to placement of structural fill soils, with exception of where quarry spalls are used as foundation material. The soils encountered at the site are silty and could be readily disturbed by traffic when wet. Therefore, we recommend that the contractor take r precautions to maintain a dry construction site and protect the subgrade from disturbance. The contractor should be prepared to control water seepage from precipitation or groundwater with the use of interceptor trenches or pumped sumps. Surface water should be diverted away from rthe pipeline and manhole excavations by means of berms, swales, French drains, or sloping of grades away from the construction area. rTemporary Slope and Shoring Considerations The stability of temporary cut slopes made during the site work is a function of many factors, r including, but not limited to, the following considerations: 1) the presence and abundance of surface water and groundwater; 2) type and density of the various soil strata; 3) the depth of the cut; 4) surcharge loadings adjacent to the excavation; and 5) the length of time the excavation remains open. Consequently, it is exceedingly difficult to establish a safe and maintenance-free cut slope angle in advance of construction. Cut slope stability should, therefore, be the responsibility of the contractor, since he is continuously at the job site, able to observe the nature and condition of the subsurface materials encountered, monitor the cut performance, and control the scheduling of site activities. r We recommend that excavations greater than 4 feet in vertical height be adequately sloped or braced to prevent injury to workmen from localized sloughing and spalling. All excavations should be accomplished in accordance with applicable local, State, and Federal safety provisions. As recommended in OSHA/WISHA guidelines for Type C soils, cuts in the fill and loose granular native soils should be not steeper than 1.5H:1 V. Under adverse weather conditions, temporary slopes should be draped with Visqueen or other means to protect them ' from the elements and minimize sloughing and erosion. At locations where safe slope angles cannot be accommodated, or in other areas of high groundwater or fill soils, and where sloughing of the excavation sides could endanger either workers, or other features, we recommend that adequate shoring be utilized. We anticipate r that a steel strutted trench box, braced sheeting, or braced sheet piling could be utilized in any areas where sloughing and/or caving of the trench sidewalls would endanger workers or features adjacent to the trench. Design of trench shoring should be the responsibility of the contractor and should be capable of retaining lateral pressures as discussed below. r ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 9 For the manhole structures, a braced sheeting system would be recommended if safe slope angles cannot be accommodated. A "tight" sheeting system would consist of pre-installed steel or timber sheets advanced to approximately 1 to 2 feet below proposed excavation bottom. The sheets would be laterally supported by means of hydraulic cross braces installed at ' designated depth(s) (determined by design) as excavation progresses. In this manner, employees can be protected from cave-in and the risk of collapse of adjacent structures can be minimized. The shoring should be installed in such a manner so as to minimize ground vibrations. To this end, an internally braced system would be desirable since a fully cantilevered system would require significant penetration of the sheets into the hard native soils to obtain adequate passive resistance; hence, significantly increasing the amount of driving and ' associated ground vibration. The contractor should be made responsible for the design, installation, and maintenance of an appropriate method of sidewall support for the excavation and any required dewatering. For design of a shoring system with only one level of internal bracing, a triangular active earth pressure distribution may be assumed using an equivalent fluid pressure (EFP) value of 47 pounds per cubic foot (pcf). For design of a shoring system with two or more levels of internal bracing, a rectangular active earth pressure distribution with a maximum pressure of 27H ' pounds per square foot (psf) should be used, where H is the height of the excavation, in feet. Alternatively, the shoring may be designed in accordance with WAC 296-155-66105 (or 66103) for Soil Type C. Any alternative shoring systems proposed by the contractor must be 1 submitted to the owner and/or his agents for review prior to construction. Permanent Slope Stability Considerations Based upon our site reconnaissance and subsurface explorations, there does not appear to be a deep-seated global stability problem along the alignment of the stormwater outfall. Previous episodes of earth movement appear to be related predominantly to the method of outletting storm water from the upslope catch basin, compounded to a lesser degree by natural surface water runoff from precipitation. Tightlining the outfall as planned should significantly reduce both channel scour and bank erosion/sloughing at the top of the slope. The existing geotextile fabric lining at the top of the slope and extension of the CMP outfall further downstream appears to have slowed the erosion process; however, the scarp has still become wider, and can continue to both widen and cut back into the bank of the neighbors property. In order to 1 more aggressively slow down the ongoing bank erosion, we recommend that the oversteepened portion of the bank either be covered with an impermeable plastic membrane or applied with a reinforced shotcrete facing. We would be pleased to provide details on either of these ' methods, or other alternatives at a later time, if requested. Design of Buried Structures The following parameters may be used for design of buried structures. We recommend that the detailed design of buried structures be reviewed by AEE as the project proceeds. These ' design parameters should be reviewed based on the structures they are being used for. ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 10 • Lateral pressure = 95 pcf* triangular distribution • Allowable Bearing Pressure = 2,000 psf** 1 • Unit weight of soil cover = 125 pcf * Assumes full hydrostatic head and at-rest pressure conditions. 1 "Assumes subgrade prepared as recommended in "Site Preparation and Structural Fill" section of this report. Pipe Anchorage Considerations Special considerations needed to be taken for a pipe outfall laid on a slope include providing an adequate connection to the wall of the catch basin and providing restraint against lateral movement. Several methods are available for accomplishing these requirements. We recommend that the pipe manufacturer or contractor provide a tensile and shear connection ' detail between the catch basin/drop structure and the outfall pipe which will prevent the pipe from pulling out. Similarly, the wall of the catch basin must be of adequate strength to withstand the loading imposed by the outfall pipe. A typical connection will consist of a flange 1 adaptor with a grooved lip and a two piece steel clamp mortared into the catch basin. We recommend that the HDPE pipe be anchored at each joint, typically every 40 feet. A typical anchorage would consist of a pipe collar pinned to the slope with rebar or some other form of metal spike. CLOSURE ' The conclusions and recommendations presented in this report are based on the explorations accomplished for this study and our understanding of the project at this time. The number, locations, and depths of the explorations were completed within the site and work scope 1 constraints so as to yield the information needed to formulate our recommendations. AGRA Earth & Environmental, Inc. would be available to provide geotechnical engineering services during the construction phase of this project. In the event that variations in the subsurface conditions are observed at the time, we would be available to provide additional geotechnical recommendations to minimize delays as the project develops. ' ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 11 We trust that this report serves your immediate needs. We appreciate the opportunity to ' provide these services. If you should have any questions, or need additional information, please do not hesitate to call at your convenience. Respectfully submitted, AGRA Earth & Environmental, Inc. ' Curt R. Thompson Senior Project Geo gist Benjamin eiss, P.E. Senior Project Engineer //�/7^ EMPIRES lJ isAN z IAA-11 It )John E. Zipper, P.E. �'13TE4 ti'� Senior Associate NAL� � Enclosures: Figure 1 - Location Map r97PIRES 1 241 q-1 Figure 2 - Site and Exploration Plan, Outfall Figure 3 - Geologic Profile Figure 4 - Site and Exploration Plan, Outlet Structure Appendix A - Subsurface Exploration Logs Appendix B - Laboratory Test Procedures and Results i i ' ,AGRA Earth & Environmental CMP backfill — slope fill — Very loose to loose, 340 silty SAND with some gravel to gravelly CATCH BASIN 340 Qit — Recessional kome terrace 12" CMP deposits — Loose to medium B_ dense SAND — gravelly SAND 320 Fill 2 - - -- - 320 Very stiif to hard, Qit _ _ — _ Qu —undifferentiated Till sandy SILT to silty SAND layers and interbedded Glacilfluvial SAND - 16 300 gravelly SAND 28 Qu 32 ? 300 Quarry spalls 34 280 on surface Qu 280 Medium dense to dense, SAND gravelly SAND Qu — Dense, silty SAND — — — — — — — — — — — — — —? ' 260 SANDSTONE 260 F— Lv r 240 Renton Formation (Tr) LEGEND 240 Z O — — — —F INTERFACE LINE 220 - - _, 220 LLI J - - - C_COAL ' W — — — COAL aid SILTSTONE DEBRIS 200 - - - - _ COAL Debris Dam Debris Dam — — — — SILTSTONE—_ 200 ' trees and soil — Quarry spalls and trees SANDSTONE B_1 BORING NUMBER AND accumulated sands, silts APPROXIMATE LOCATION 180 gravels from upslope I STANDARD PENETRATION TEST 180 ' 1 — BLOWS PER FOOT 160 - - - - - - - - -? 160 NOTE: THE STRATA ARE BASED UPON SILTSTONE INTERPOLATION OF OUR TEST BORING AND FIELD RECONNAISSANCE AND PUBLISHED 140 GEOLOGIC LITERATURE AND MAY 140 NOT REPRESENT ACTUAL — — — — — —? SUBSURFACE CONDITIONS. SANDSTONE — SILTSTONE — COAL SEAM 120 120 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40 -60 -70 -80 -100 DISTANCE IN FEET ALONG OF PROFILE FIGURE 3 ' W.O. 11-10496-01 HIGH AVENUE SOUTH OUTFALL W A® R A DESIGN CRT RENTON, WASHINGTON Earth &Environmental DRAWN JMR 11335 N.E. 122nd Way, Suite 100 DATE JAN 1996 GROUND SURFACE GEOLOGIC PROFILE Kirkland, WA, U.S.A. 98034-6918 1"=30' SCALE ' AGRA EARTH k ENVIRONMENTAL, INC. DRAWING NO. 11 10496 X-S-A.DWG Io QO� TP--5 o Y i ' 0 20 40 �-- SCALE IN FEET 1 � w TP-3 ' o DRAINAGE.,_ PATN 120 OUTLET STRUCTURE l9 TP-2 / T o 1130 �x I ' 'SO \ Iwo i PTP1 NEW 12" SHDPE PIPE LEGEND / i 0 ls0 TP�-5 TEST PIT NUMBER AND p� APPROXIMATE LOCATION U C FIGURE 4 E W.O. 11-10496-01 HIGH AVENUE OUTFALL ' 5 AG R A DESIGN cRT RENTON, WASHINGTON Earth & Environmental DRAWN DMW w 11335 NE 122nd Way, Suite 100 DATE MAY 1996 SITE 8 EXPLORATION PLAN ' OUTLET STRUCTURE < Kirkland, Washington, U.S.A. 98034-6918 SCALE 1 20 c� — Appendix A 1 APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS 11-10496-01 ' ,AG RA Earth & Environmental 1 ' APPENDIX A 11-10496-01 ' SUBSURFACE EXPLORATION The field exploration program conducted for this study consisted of advancing one hollow-stem auger test boring and excavating five test pits. The exploration locations were obtained in the field by pacing from site features shown on a site map provided us. The approximate locations of our explorations are indicated on the Site and Exploration Plan, Figure 2. The locations of the explorations should be considered accurate only to the degree implied by the method used. ' Hollow-Stem Auger Boring The test boring was drilled by a local exploration drilling company under subcontract to our firm on 16 January 1996. The boring consisted of advancing a 4%Z inside diameter (ID) hollow-stem ' auger with a truck-mounted CME 85 drill rig. During the drilling process, samples were obtained at generally 2.5 to 5.0 foot depth intervals. The borings were continuously observed and logged by an engineering geologist from our firm. Disturbed samples were obtained by using the Standard Penetration Test procedures as described in ASTM:D 1586. This test and sampling method consist of driving a standard 2-inch ' outside diameter split barrel sampler a distance of 18 inches into the soil with a 140 pound hammer free-falling a distance of 30 inches. The number of blows for each 6-inch interval is recorded. The number of blows required to drive the sampler the final 12 inches is considered the Standard Penetration Resistance ("N") or blow count. The blow count is presented graphically on the boring logs in this appendix. If a total of 50 blow is recorded within one 6- inch interval, the blow count is recorded as 50 blows for the number of inches of penetration. The resistance, or "N" value, provides a measure of relative density or granular soils or the relative consistency of cohesive soils. ' The soil samples obtained from the split-barrel sampler were classified in the field and representative potions were placed in plastic containers. The samples were then transported ' to our laboratory for further visual classification and laboratory testing. Samples are generally saved for a period of 30 days unless special arrangements are made. The boring log presented in this appendix is based on the drilling action, inspection of the samples secured, laboratory results, and the field log. The various types of soils are indicated, as well as the depths where the soils or characteristics of the soils changed. It should be noted ' that these changes may have been gradational, and if the changes occurred between sample intervals, they were inferred. ' The groundwater conditions observed during the exploration program are indicated on the boring or test pit logs, where appropriate. The subsurface water conditions were evaluated by observing the free water on the sampling rods for the boring explorations and moisture ' conditions of the samples and side walls for the test pits. The groundwater level is indicated on the boring logs by a triangular symbol and the designation "ATD" (At Time of Drilling). The groundwater depth shown on the boring log is generally indicative of the open water level in 1 ' ,AG RA Earth & Environmental ' the boring at the time the boring was advanced, but does not necessarily represent the true regional groundwater table. ' Test Pit Excavations ' Five test pits were excavated on 15 January 1996 with a track-mounted backhoe operated by a local excavation contractor. Each test pit was continuously logged and observed by one of our experienced engineering geologists. In-situ strength and quality attributes of materials ' encountered in the test pits were estimated by our field observer based on experience with similar soils and on the difficulty incurred during excavation. Disturbed, but representative, samples of the soils in the test pits were retrieved, classified in the field, and transported in plastic containers to our laboratory for further evaluation and classification. The test pit logs presented in this appendix are based on inspection of the soil samples and the field logs. AG R A Earth & Environmental PROJECT: High Avenue South Outfall wo. 77- 70496-07 BORING NO. B- 7 SOIL DESCRIPTION W 5 PENETRATION RESISTANCE Page I . Location: See Site Plan AL L of 2 ix Standard Blows per foot Other Approximate ground surface elevation: 326 feet Cn 0 1 1 0 0 10 20 30 40 50 TESTING Crushed Rock(Fill) NIE ------------------------------- ---------------- .............................. ------------------------ Very loose,moist,brown,silty,gravelly SAND with some organics(Fill) ---------------------- ................ ------- ------------- ......................... S-1 ............................................................... ------------------------------- 5 Loose,moist,brown,fine to medium SAND with some coarse sand,trace gravel,slit and S-2 0.. ............... organics ............................ ------ ............... ..... ............................................. ....... ....... ............... ....... ....... ....... ---------------- S-3 ..... ..........i ................................... .......:........ - 10 N, ---------------------- Very stiff to hard,moist,brown,sandy SILT with S-4 • ------------ ................------- trace to some gravel and Interbedded oxidized orange,fine to medium SAND(114'- 112'zones) ....... .......... ................................ ....... ------- ---------------............ S-5 ................ ------- .............................. 15 S-6 ...............................-------- - .......... .............. ---------------........ T Very stiff,moist,brown/gray,sandy SILT with somegravel ......... .......................... ---------------- ....... S-7 ................ ---- ------- ................ .......... 20 ....... --------------------------------------------- ------- ----- ........... ............................... ....... Grades with some clay,trace grovel ....... ....... ------- .............................. ............... S-8 • ........................ --------- .................................... - 25 ----------- ------------------- ........ ---------------------- ..................................... Hard,moist to wet,brown/gray,sandy SILT with some grovel and interbedded oxidized orange, 7............................... ............... ....... ................. fine to medium SAND(114'- 112'zones) . ...................... ...............--------- ............. ................. S-9 ....... ------- ----------- ------ 30 (continued) - -Li 0 20 40 60 80 100 LEGEND MOISTURE CONTENT cc 1 c E C Plastic limit Natural Liquid limit 2 2.00-inch OD split-spoon sample Grain size analysis >c: LU AG R A Earth & Environmental wNIE No groundwater encountered 11335 NE 122nd Way,Suite 100 Kirkland,Washington 98034-6918 ' a Drilling method: HSA Hammer type: Automatic Date drilled: 16 January 1996 Logged by: CRT PROJECT: High Avenue South Outfoll w.o. 1 1- 10496-0 1 BORING NO. B- 1 ' r _ SOIL DESCRIPTION c�c w PENETRATION RESISTANCE Page 2 U 8 Location: See Site Plan A IL of 2 (� < d a 3 Standard Blows per foot Other Approximate ground surface elevation: 326 feet a 0 10 20 30 40 50 TT=a 30 Some as above N/E ———— ---------------- ------- --------------- .....---------- --------------- Dense,moist,brown,tine to medium SAND with ' trace coarse sand,gravel and silt -- - -- ... ... - -- :.. .... .. ......... ........ •....... .. ..<- --- S-10 .=-----. -- ... 35 ————- ------ ......... Grades with coarser SAND,some gravel to ' gravelly ... .....,-------........=----------- ................?------- S-17 I : ' Boring terminated at approximately 40 39 feet --- --- .. ... ... .. - -- - -------------- 45 --- -- - -- -- -- .. -- .......................... -- --- ----- -- --- ----- 50 ......................... ----- -.. --- ... ....... ....... ................ 55 ..........................------- . ... ... ... .. . .... 60 0 - 20 40 60 80 100 MOISTURE CONTENT LEGEND c Plastic limit Natural Liquid limit I2.00-inch OD split-spoon sample ® Grain size analysis Lu MR, AG R A ' Earth & Environmental t N/E No groundwater encountered W e 11335 NE 122nd Way,Suite 100 Kirkland,Washington 98034-6918 a Drilling method: HSA Hammer type: Automatic Date drilled: 76 January 1996 Logged by: CRT TEST PIT LOGS 1 1-1 0496-0 1 Depth (feet) Material Description Test Pit TP-1 tLocation: See Site Plan Approximate ground surface elevation: Unknown ' 0.0 - 3.0 Forest duff atop very loose, moist to wet, dark brown, silty SAND to sandy SILT with some organics, gravel, coal, brick ' fragments and substantial roots (Fill and/or Colluvium). 3.0 - 10.0 Loose to medium dense, wet, brown/gray, silty SAND with some gravel, coal and wood fragments (Fill and/or Colluvium). ' 10.0 - 13.0 Medium dense, moist to wet, tan-brown, silty SAND with some gravel (Weathered Sandstone). ' Test pit terminated at approximately 13.0 feet Severe caving at 0 to 10.0 feet Slow seepage at 3.0 feet Moderate seepage at 10.0 feet Test Pit TP-2 Location: See Site Plan Approximate ground surface elevation: Unknown ' 0.0 - 2.5 Forest duff atop soft, moist to wet, black, sandy SILT with some organics, gravel and substantial roots (Fill and/or Colluvium). 2.5 - 9.0 Loose to medium dense, wet, brown, silty SAND with some gravel, coal and wood fragments (Fill and/or Colluvium). 9.0 - 11.0 Medium dense, wet, blue-gray, silty SAND with some gravel. Test pit terminated at approximately 11.0 feet Severe caving from 0 to 9.0 feet Moderate seepage at 3.5 feet Rapid seepage at 9.0 feet 1 1-1 0496-01 Test Pit Log, Page 2 Depth (feet) Material Description Test Pit TP-3 Location: See Site Plan Approximate ground surface elevation: Unknown 0.0 - 1 .5 Forest duff atop very loose, moist to wet, brown-gray-black, ' silty SAND with some organics, gravel and substantial roots (Fill and/or Colluvium). 1 .5 - 10.0 Loose, wet, brown-gray-black, gravelly, silty SAND with some wood, coal, and moderate roots to 3.0 feet (Fill and/or Colluvium). 10.0 - 12.0 Medium dense, wet, gray, silty SAND with some gravel and ' interbedded sandy SILT. Test pit terminated at approximately 12.0 feet Moderate to Severe caving 0 to 10 feet Rapid seepage at 5.0 feet Test Pit TP-4 Location: See Site Plan Approximate ground surface elevation: Unknown ' 0.0 - 3.0 Forest duff atop very soft, wet, brown, sandy SILT with some clay, wood debris including timbers, trace gravel, and moderate ' roots (Fill and/or Colluvium). 3.0 - 8.0 Soft, wet, brown-gray, sandy SILT with some clay, brick, and coal fragments and wood debris including timbers (Fill and/or IColluvium). Test pit terminated at approximately 8.0 feet Severe caving 0 to 8.0 feet, requires stoppage due to caving conditions Moderate surficial seepage Rapid seepage at 1.5 feet i 1 1-1 0496-01 Test Pit Log, Page 3 ' Depth (feet) Material Description Test Pit TP-5 Location: See Site Plan Approximate ground surface elevation: Unknown 0.0 - 1.5 Forest duff atop very loose, wet, black, silty SAND to sandy SILT with some organics, trace gravel and substantial roots (Fill ' and/or Colluvium). 1.5 - 3.0 Loose, wet, brown-gray, silty, gravelly SAND with some organics and substantial roots (Fill and/or Colluvium). ' 3.0 - 8.0 Loose, saturated, brown-gray, silty SAND with some gravel, logs, wood debris and coal (Fill and/or Colluvium). 8.0 - 10.0 Medium dense, wet, blue-gray, silty SAND with some gravel. ' Test pit terminated at approximately 10.0 feet Severe caving 0 to 8.0 feet ' Rapid seepage at 3.0 feet Date excavated: 15 January 1996 Logged by: CRT r r Appendix B ' APPENDIX B LABORATORY PROCEDURES AND RESULTS 11-10496-01 ' ,AG RA Earth & Environmental APPENDIX B 11-10496-01 LABORATORY TESTING PROCEDURES A series of laboratory tests were performed during the course of this study to evaluate the index and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests performed are given below. Visual Classification 1 Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in watertight containers and transported to our laboratory where the filed classifications were verified or modified as required. Visual classification was generally done in accordance with the Unified Soil Classification system. Visual soil classification includes evaluation of color, relative moisture content, soil type based on grain size, and accessory soil types included in the ' sample. Soil classifications are presented on the boring and test pit logs in Appendix A. Moisture Content Determinations ' Moisture content determinations were performed on representative samples obtained from the explorations in order to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM:D-2216. The ' results of the tests are listed in this Appendix and presented on the boring log in Appendix A. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. A grain size analysis was performed on representative samples in general accordance 1 with ASTM:D-422. The results of the grain size determination for the samples were used in classification of the soils, and is presented in this Appendix. r ,AG RA Earth & Environmental MOISTURE CONTENT 1 Job Name: High Ave. South Outfall Job Number: 1 1-1 0496-01 Date: 1-17-96 Exploration: B-1 B-1 B-1 B-1 B-1 B-1 TP-1 TP-2 TP-2 TP-3 Sample Number: S-1 S-2 S-6 S-8 S-9 S-11 Depth: 2.5' 5.0' 15.9 22.5' 27.5' 37.5' 3.0-10.9 0.0-2.5' 2.5-9.9 0.0-1.5' Wet weight: ' Dia. of sample: Length of Sample: Volume (cf): ' Wet Density: Dry Density: Wet sample +tare: 347 475 538 424 607 651 714 492 586 692 ' Dry sample+tare: 335 458 500 375 528 637 645 419 532 619 Water: 12 18 38 49 79 14 69 73 54 73 Tare: 161 162 162 169 162 161 167 155 165 167 Moisture Content: 7% 6% 11% 24% 22% 3% 14% 27% 15% 16% Exploration: TP-3 TP 4 TP 4 Sample Number: ' Depth: 10.412.0' 0.0-3.9 3.0-8.0' Wet weight: Dia. of sample: Length of Sample: Volume (cf): Wet Density: Dry Density: Wet sample +tare: 725 664 646 Dry sample +tare: 637 541 523 Water: 88 123 123 0 0 0 0 0 0 0 ' Tare: 167 163 155 Moisture Content: 19% 33% 33% Exploration: Sample Number: Depth: Wet weight: Dia. of sample: Length of Sample: Volume (cf): Wet Density: Dry Density: 1 Wet sample+tare: Dry sample+tare: Water: 0 0 0 0 0 0 0 0 0 0 Tare: Moisture Content: 1 i GRAIN SIZE DISTRIBUTION 1 SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER 36' 12" 6' 3" 1 1/2" 3/4" 3/8' 4 10 20 40 60 100 200 100- 90— "7 1 80 1 70------ 60 \ 1 } m W � 1 w � U 1 W 30 a 20 10 o 1000.00 100.00 10.00 1.00 0.10 0.01 0.00 GRAIN SIZE IN MILLIMETERS Coarse Fine Coarse Medium Fine Sift Clay WD F Exploration Sample Depth Moisture Fines Soil Description B-1 S-3 7.5' 8% 2% SAND,trace silt • •-�-�-+ B-1 S-4 10.9 15% 48% Sandy SILT,trace gravel - TP-3 1.5-10.0' 27% 32% Gravelly Silty SAND 1 Project: High Ave South Outfall 0 AGRA Work Order: 11-10496-01 Earth & Environmental Date: 1-17-96 11335 NE 122nd Way Suite 100 1 Kirkland, Washington 98034-6918 1 e * AGRA AGRA Earth& Environmental, Inc. ' Earth & Environmental 11335 NE 122nd Way Suite 100 Kirkland, Washington U.S A. 98034-6918 Tel (206) 820-4669 Fax (206) 821-3914 15 May 1996 ' 1 1-1 0496-01 City of Renton Planning/Building/Public Works Department Municipal Building 200 Mill Avenue South Renton, Washington 98055 Attention: Mr. Ronald J. Straka, P.E. Engineering Supervisor ' Subject: Subsurface Exploration and Geotechnical Engineering Study High Avenue South Outfall 525 High Avenue South Renton, Washington Gentlemen: This report presents the results of our subsurface exploration and geotechnical engineering study for the above referenced project. The purpose of this study was to interpret general surface and subsurface site conditions from which we could formulate a summary discussion regarding general site stability, temporary open cut slope and shoring considerations, and soil design parameters for the excavation and replacement of the upslope storm water catch basin and piping. Recommendations regarding support for the proposed High Density Polyethylene (HDPE) piping down the slope to the concrete energy dissipator/diffusion structure are also discussed. Our scope of services consisted of a visual site reconnaissance, subsurface exploration, laboratory testing, geotechnical analysis, and preparation of this report. Our work has been performed in accordance with our scope of geotechnical services dated 14 November 1995 and our on-call consultant contract with the City of Renton. Authorization to proceed with this study was granted by the City of Renton on 4 January 1996. This report has been prepared for the exclusive use of the City of Renton, and their agents for specific application to this project in accordance with generally accepted geotechnical engineering practices. ' SITE AND PROJECT DESCRIPTION The storm drain outfall is located at the north end of High Avenue South, northeast of a ' residence located at 525 High Avenue South in Renton, Washington. The storm drain outfall Engineering& Environmental Services City of Renton 1 1-1 0496-01 15 May 1996 Page 2 is a 12-inch diameter corrugated metal pipe (CMP) which serves as the discharge for the collected upland surface water. The nearest catch basin for the CMP is approximately 75 feet south of the top of slope and 90 feet south of the outfall. The storm water discharges from the pipe near the top of the slope and follows a drainage channel steeply downslope. ' We performed a preliminary eotechnical memorandum in late August 1995 to assess impacts P P 9 ' to the storm drain line and future slope stability after a landslide occurred following heavy rains on 16 August 1995. Additional observations on 9 October 1995 disclosed substantial channel cutting and loss of bank soils in the discharge area compared to our 31 August 1995 geologic ' reconnaissance. The City of Renton performed temporary erosion control measures in mid October 1995 including a tightline extension to the outfall pipe, and placement of geotextile fabric atop the upper exposed slope soils and below the tightline pipe. ' We understand the City of Renton plans to reconstruct the existing outfall with a HDPE tightline. A new upslope catch basin inlet manhole will replace the existing catch basin and serve as the start of the HDPE tightline. The HDPE tightline will exit the catch basin at a depth of approximately 10 to 15 feet below the top of slope and then continue atop the surface of the drainage channel to its terminus at a new downslope energy dissipator/diffusion structure. In the event of any changes in the nature or design of this project, the conclusions and recommendations contained in this study should be reviewed and modified, as necessary, to ' reflect the changes. SITE CONDITIONS The site conditions were evaluated for this study in August and October 1995, and January 1996. The surface and subsurface conditions are described below, while the exploration procedures and interpretive logs of the explorations are presented in Appendix A. The general project vicinity is shown on the Location Map, Figure 1. The approximate locations of the explorations are indicated on the Site and Exploration Plan, Figures 2 and 4. Laboratory ' procedures and test results are presented in Appendix B and on the exploration logs, where appropriate. ' Surface Conditions The site is located at the north end of High Avenue South, northeast of the residence located at 525 High Avenue South, in Renton, Washington. The upslope area includes a catch basin within the asphalt roadway/driveway, a gravel parking area, a landscaping berm including beauty bark and plantings and grass covered areas. The eroded slope area adjacent to the existing outfall pipe where landsliding has occurred is approximately 35 to 40 feet in width and ' 25 to 30 feet in height. In mid October 1995, the City of Renton extended the outfall pipe further downslope and placed geotextile fabric atop the upper exposed slope and below the tightline pipe extension to reduce further erosion. ' ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 ' 15 May 1996 Page 3 The drainage channel below the outfall was surficially covered with quarry spall rock (4- to 8- inch) in the splash area and a limited area further downslope. The slopes adjacent to the drainage channel were generally covered with surface brush, blackberries, and small alder and maple trees. The trees on the slope have been regularly topped for the downtown view to the northwest. A 10- to 20-foot high pile of accumulated trees, root mass, brush, soil, quarry spall rock, and debris including concrete and CMP is located at the base of the upper slope within the drainage channel. The debris pile is on the order of 60 feet in length. A smaller debris pile consisting of finer debris, wood, and soil is located downslope of the large debris dam. An alluvial fan type soil deposit is located below the debris piles in the area of the proposed energy dissipator/diffusion structure. The topography becomes less severe in this area where soil is deposited during outfall runoff. Further downstream, the drainage channel cuts through waste piles of coal, siltstone, and ' sandstone to pond at the base of the slope in the proposed City of Renton park site. During a heavy rain event, we observed that the runoff drained to a catch basin at the northwest area of the proposed park. ' Subsurface Conditions To assess subsurface conditions we performed an exploration program including one test boring ' at the top of the slope and five trackhoe excavated test pits in the area of the proposed energy dissipator/diffusion structure near the bottom of the slope. The test boring disclosed approximately 4.5 feet of fill soils consisting of a very loose to loose silty gravelly sand with some organics atop a recessional deposit consisting of loose sand with trace gravel, silt and organics. At a depth of approximately 10.5 feet to 31 feet, we ' encountered a very stiff to hard sandy silt with some gravel and interbedded sand. A dense sand with trace gravel and silt was encountered at approximately 31 feet in depth and graded to gravelly at 36 feet to the total depth of the boring at 39 feet. Below the recessional ' deposits at 10.5 feet, the soils are classified as undifferentiated deposits which include three or more glacial till sheets, glaciofluvial sand and gravel, glaciolacustrine clay and sand, and non- glacial sand, clay, and thin peat. The trackhoe excavated test pits in the area of the proposed energy dissipator/diffusion structure disclosed approximately 8 to 10 feet of fill and/or colluvium consisting of a loose, silty sand to sandy silt with some gravel to gravelly and coal, wood, and brick fragments. Native, medium dense silty sand with some gravel was typically encountered below the upper loose soils in the test pits. Moderate to severe caving of the test pit walls was observed within the fill soils. Test pit TP-4 encountered wood timbers within the fill soils. It would appear that the fill and/or colluvium encountered in the test pits is related to mining of resources of coal and ' siltstone from the site area. A brick manufacturing company existed downslope at the A G R A Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 4 proposed park site, which mined the siltstone (shale) for brick manufacturing. As mining of resources was conducted, the spoils remained at the base of the slope. Though our test pit explorations were limited, areas of mounded spoils, and disturbance to the area was observed across the lower slope areas. In addition, downslope movement of surficial soils including ' slumps (colluvium) were observed in the lower slope area of the project site. Groundwater was not observed in our test boring at the top of the slope, but was observed as moderate to rapid seepage at depths ranging from about 1.5 to 10 feet in all five test pits at the bottom of the slope. It should be noted that seepage from precipitation may at times become "perched" within the fill and/or atop the dense silty sands and hard sandy silts of the undifferentiated deposits in the upper slope area. If perched water is encountered, the proposed outfall design improvements should not require further modification. Please refer to ' our recommendations in the site preparation, drainage and slope considerations sections of this report as they relate to groundwater seepage. GEOLOGIC RECONNAISSANCE We performed a geologic reconnaissance of the drainage channel slope for our previous study on 31 August 1995. For this study, we performed a ground surface geologic profile of the ' slope and incorporated our test boring advanced at the top of the slope. We visually observed site conditions and channel soil contacts during our site reconnaissance on 22 January 1996. The topographic information, based on a City of Renton supplied topographic plan, shows a top of slope elevation of approximately 326 feet and 55 feet at the bottom of the slope. The toe of the accumulated upslope debris, spalls, etc. is approximately elevation 160 feet. The proposed energy dissipator manhole structure will be at approximately elevation 140 feet. I Presented below is a summary description of the channel soil contacts observed during our site reconnaissance. The existing slope profile and soil contacts are shown on Figure 3, Ground Surface Geologic Profile. ' Our test boring generally correlated with the exposed soil contacts in the drainage channel. Approximately 5 to 8 feet of very loose, silty, gravelly sand fill was observed atop 5 to 6 feet ' of loose sand with trace gravel. This native sand is mapped as recessional stratified drift, Qit, kame terrace deposits. The Renton Quadrangle Geologic Map, 1965, describes the Kame ' terrace deposits as sand and pebble to cobble gravel in scattered terraces whose surfaces locally are deformed by extensive collapse. The fill and recessional soils have formed a near vertical slope (.5 Horizontal:1 Vertical) from the top of slope to approximately 5 feet below the outfall in the drainage channel. Below the recessional deposits and approximately 5 feet vertically below the outfall pipe, we observed a 15-foot near vertical slope of glacially consolidated, very stiff to hard sandy silt with some gravel, mapped as Qu, undifferentiated deposits. The undifferentiated deposits include three or more till sheets, glaciofluvial sand and gravel, glaciolacustrine clay and sand, and non-glacial sand, clay, and thin peat. ' L,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 5 We observed Qu deposits of interbedded silty sands, sandy silts, and gravelly sands in our test ' boring and along the drainage channel and banks for approximately 60 feet on a slope on the order of 1 H:1 V (Horizontal:Vertical). Our test boring encountered a sand interbed of the Qu deposit from approximately 31 feet to the boring bottom depth of 39 feet. Though not encountered in the test boring, the sandstone (which is mapped as the Renton Formation (Tr)) was observed in the drainage channel approximately 60 feet downslope from the base of the ' near vertical slope below the outfall. A layer of quarry spall rock (4 to 8 inches in size) and geotextile fabric covers the upper drainage channel below the outfall to approximately the sandstone contact. The Renton Formation consists of arkosic sandstone, mudstone, shale, and coal beds. This formation is characterized by numerous faults of small displacement, wavy bedding, and a thickness of approximately 2,500 feet. The coal and shale (siltstone) from this formation was mined extensively in Renton, including beneath the project area. The observed upper sandstone forms a 1 H:1 V slope (similar to the Qu deposits) for approximately 15 feet and then drops vertically approximately 20 feet. The sandstone in the drainage channel has formed steps with interbedded coal and siltstone for approximately 100 feet. The steps form an overall slope on the order of 1 .25H:1 V. ' A 10- to 20-foot high pile of accumulated trees, root mass, brush, soil, quarry spall rock, and debris including concrete and CMP is located at the base of the upper slope at approximately elevation 165 feet. The debris pile is on the order of 60 feet in length. A smaller debris pile consisting of finer debris, wood, and soil is located downslope of the large debris dam. A siltstone horizon of the Renton Formation was observed beneath the debris piles. Further ' downslope, we observed interbedded sandstone, siltstone, and coal along the drainage channel. In the area of the proposed energy dissipator manhole structure, an alluvial fan type soil deposit is located where the topography becomes less severe. The runoff channel in this area deposits sediment rather than downcutting a deeper channel. Downslope movement of surficial soils including slumps and/or colluvium are evident in the lower areas of the channel. The lower areas also contain fill, as observed in our test pits, which relate to the mining of the siltstone and coal from the area. Groundwater seepage from the upper slope was not evident during our site reconnaissance. We observed surficial seepage in the area of the test pits in the lower slope area. Refer to the ' test pit logs for noted surficial seepage and depths of observed seepage. CONCLUSIONS AND RECOMMENDATIONS Development plans call for removal of the existing catch basin structure on High Avenue South and the approximately 90 feet of existing corrugated metal pipe (CMP) to the north. Replacement with a new concrete manhole and 12-inch diameter high density polyethylene (HDPE) pipe is planned. The HDPE pipe will tightline the storm water down the surface of the ,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 6 slope to an energy dissipator/diffusion structure near the base of the slope. The proposed energy dissipator/diffusion structure will be a 54 to 72 inch diameter partially buried manhole structure where the HDPE tightline will enter near the ground surface. The outlet pipe from the structure will be higher than the inlet to dissipate the energy of the storm water. ' Improvements to the storm water outfall are necessary to lessen the erosion and downcutting of the drainage channel in the upper slope area and possible damage to the existing CMP ' outfall. Site Preparation and Structural Fill ' Based on our test boring, the top of slope area at the boring location consists of approximately 4.5 feet of very loose to loose silty, gravelly sand fill atop approximately 6 feet of loose sand ' (recessional deposits). At 10.5 feet in depth to approximately 31 feet, a very stiff to hard sandy silt interbedded with sand was encountered. A majority of the excavation for the new upper catch basin manhole and HDPE pipe, planned at a depth of approximately 10 to 15 feet below existing grade, will encounter the existing fill soils, loose recessional sands, and possibly the very stiff to hard sandy silts. The exposed subgrade surface for the catch basin structure should be free of loose/disturbed soil or standing water and compacted such that an in-place soil density of at least 90 percent is achieved to a depth of 12 inches, using the ASTM:D-1557 modified Proctor maximum dry density. We recommend a bedding material for the catch basin suitable for rigid pipe consisting of crushed, partially crushed, or naturally occurring granular material free from wood waste and organic material and having a maximum dimension of 1 inch. The bedding material should conform to the gradation described in Section 9-03.15 of the 1994 WSDOT/APWA Standard Specifications. If any organic or unsuitable soils are encountered at the proposed pipeline subgrade, overexcavation to expose suitable competent material would be necessary. Backfill should consist of compacted Class A, Class B, or Class C Foundation Material as described in Sections 9-03.17 and 9-03.18 of WSDOT/APWA Standard Specifications. Controlled Density Fill (CDF) or lean concrete may be used as an alternate foundation and backfill material. According to manufacturer specifications, no bedding material is required below HDPE pipe. To prevent migration of water within the bedding material or backfill and potential of sloughing of the slope during compaction, use of CDF within 30 feet behind the slope is recommended in lieu of a permeable granular bedding material. Alternatively, the use of low permeability pipe collars, such as CDF, clay/bentonite or concrete collars/check dams could be installed at several locations along the buried HDPE tightline. The pipe collar should fully envelope the pipe and extend a minimum of 1-foot below the base of the trench and 1 foot above the top of the pipe bedding. We anticipate that pipe collars on the order of 3 to 4 feet in length should be ' adequate. As previously mentioned, roughly 10 feet of loose fill with debris was encountered at the proposed downslope energy dissipator location. It will likely not be practical to overexcavate LyAGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 7 and replace all the existing fill beneath the energy dissipator structure. Therefore, it is our ' opinion that overexcavation of 3 feet of unsuitable soils be performed below the structure. Due to the presence of groundwater and poor ground conditions, we recommend that quarry spalls be used as foundation backfill material for the 3 feet under the structure. The quarry spalls ' should be firmly seated into the underlying ground using the bucket of the excavator. We recommend that the quarry spall foundation mat extend laterally at least 2 feet beyond all sides of the energy dissipator structure. ' A limited length, on the order of 30 to 40 feet of HDPE pipe will be buried in the downslope pipe trench as it connects to the outlet structure. The depth of burial will vary from approximately 1 to 4 feet and bedding material is not required below the HDPE pipe. ' The suitability of soils for structural fill use depends primarily on the gradation and moisture content of the soil when it is placed. Soil to be used as structural fill should be free of organics and other deleterious material. As the amount of fines (that portion passing the U.S. No. 200 ' Sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. Soil containing more than about 5 percent fines by weight usually cannot be compacted to a firm, non-yielding ' conditions when the moisture content is more than about 2 percent above optimum. We anticipate that the on-site soils for the High Avenue work that would be available for fill as a result of trench excavation would primarily be a silty gravelly sand with some organics (old fill) and a sand with trace gravel, silt and organics. The soils disclosed in the test pits near the proposed energy dissipator location consist of loose silty sand with some gravel, wood, coal and organics (fill and/or colluvium) to a depth of approximately 10 feet. It should be realized that the on-site soils are moisture-sensitive and may be difficult or impossible to use as structural fill during wet weather or under wet site conditions. If rain were to occur while silty ' soils are exposed, or during their placement, the exposed material should be allowed to sufficiently dry prior to additional filling, as necessary to facilitate compaction. It may be necessary to scarify the upper layer, allow it to dry, and recompact prior to additional filling. It may be necessary to overexcavate and remove wet soils if it is not practical to dry and recompact them. Select "clean" granular soils would then be required for structural fill use. Select imported fill should consist of "clean" free draining, well graded sand and gravel as specified in WSDOT/APWA Section 9-03.19, "Bank Run Gravel for Trench Backfill". Imported fill soils should contain no more than 5 percent fines by weight passing through the U.S. No. 200 Sieve when measured against the minus No. 4 fraction. Material of this type may be successfully placed and compacted under a wider variety of weather conditions. Soils used for ' structural fill should have no particles greater than 2'/2 inches in maximum dimension and be free of organics and other deleterious materials. Structural fill should be placed over a properly prepared subgrade, as discussed above. Structural fill should be placed in 8-inch maximum 1 ' ,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 8 loose lifts. Each lift should be compacted to at least 90 percent of the laboratory Proctor ' maximum dry density, using ASTM:D-1557 as the standard. Drainage Considerations Based on our explorations, groundwater was not encountered in our test boring advanced at the top of slope area, but was encountered in all of the test pits at the base of slope at depths from 0 to 10 feet. The excavations for the proposed structures and pipeline should be ' dewatered as needed prior to placement of structural fill soils, with exception of where quarry spalls are used as foundation material. The soils encountered at the site are silty and could be readily disturbed by traffic when wet. Therefore, we recommend that the contractor take ' precautions to maintain a dry construction site and protect the subgrade from disturbance. The contractor should be prepared to control water seepage from precipitation or groundwater with 1 the use of interceptor trenches or pumped sumps. Surface water should be diverted away from the pipeline and manhole excavations by means of berms, swales, French drains, or sloping of grades away from the construction area. ' Temporary Slope and Shoring Considerations The stability of temporary cut slopes made during the site work is a function of many factors, including, but not limited to, the following considerations: 1) the presence and abundance of surface water and groundwater; 2) type and density of the various soil strata; 3) the depth of the cut; 4) surcharge loadings adjacent to the excavation; and 5) the length of time the excavation remains open. Consequently, it is exceedingly difficult to establish a safe and maintenance-free cut slope angle in advance of construction. Cut slope stability should, therefore, be the responsibility of the contractor, since he is continuously at the job site, able ' to observe the nature and condition of the subsurface materials encountered, monitor the cut performance, and control the scheduling of site activities. ' We recommend that excavations greater than 4 feet in vertical height be adequately sloped or braced to prevent injury to workmen from localized sloughing and spalling. All excavations should be accomplished in accordance with applicable local, State, and Federal safety provisions. As recommended in OSHA/WISHA guidelines for Type C soils, cuts in the fill and loose granular native soils should be not steeper than 1.5H:1 V. Under adverse weather conditions, temporary slopes should be draped with Visqueen or other means to protect them from the elements and minimize sloughing and erosion. At locations where safe slope angles cannot be accommodated, or in other areas of high groundwater or fill soils, and where sloughing of the excavation sides could endanger either workers, or other features, we recommend that adequate shoring be utilized. We anticipate ' that a steel strutted trench box, braced sheeting, or braced sheet piling could be utilized in any areas where sloughing and/or caving of the trench sidewalls would endanger workers or features adjacent to the trench. Design of trench shoring should be the responsibility of the contractor and should be capable of retaining lateral pressures as discussed below. ' ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 9 For the manhole structures, a braced sheeting system would be recommended if safe slope ' angles cannot be accommodated. A "tight" sheeting system would consist of pre-installed steel or timber sheets advanced to approximately 1 to 2 feet below proposed excavation bottom. The sheets would be laterally supported by means of hydraulic cross braces installed at 1 designated depth(s) (determined by design) as excavation progresses. In this manner, employees can be protected from cave-in and the risk of collapse of adjacent structures can be minimized. The shoring should be installed in such a manner so as to minimize ground vibrations. To this end, an internally braced system would be desirable since a fully cantilevered system would require significant penetration of the sheets into the hard native soils ' to obtain adequate passive resistance; hence, significantly increasing the amount of driving and associated ground vibration. The contractor should be made responsible for the design, installation, and maintenance of an appropriate method of sidewall support for the excavation ' and any required dewatering. For design of a shoring system with only one level of internal bracing, a triangular active earth ' pressure distribution may be assumed using an equivalent fluid pressure (EFP) value of 47 pounds per cubic foot (pcf). For design of a shoring system with two or more levels of internal bracing, a rectangular active earth pressure distribution with a maximum pressure of 27H pounds per square foot (psf) should be used, where H is the height of the excavation, in feet. Alternatively, the shoring may be designed in accordance with WAC 296-155-66105 (or 66103) for Soil Type C. Any alternative shoring systems proposed by the contractor must be 1 submitted to the owner and/or his agents for review prior to construction. Permanent Slope Stability Considerations Based upon our site reconnaissance and subsurface explorations, there does not appear to be a deep-seated global stability problem along the alignment of the stormwater outfall. Previous episodes of earth movement appear to be related predominantly to the method of outletting storm water from the upslope catch basin, compounded to a lesser degree by natural surface water runoff from precipitation. Tightlining the outfall as planned should significantly reduce both channel scour and bank erosion/sloughing at the top of the slope. The existing geotextile fabric lining at the top of the slope and extension of the CMP outfall further downstream appears to have slowed the erosion process; however, the scarp has still become wider, and can continue to both widen and cut back into the bank of the neighbors property. In order to more aggressively slow down the ongoing bank erosion, we recommend that the oversteepened portion of the bank either be covered with an impermeable plastic membrane or applied with ' a reinforced shotcrete facing. We would be pleased to provide details on either of these methods, or other alternatives at a later time, if requested. 1 Design of Buried Structures The following parameters may be used for design of buried structures. We recommend that the detailed design of buried structures be reviewed by AEE as the project proceeds. These design parameters should be reviewed based on the structures they are being used for. ' ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 10 • Lateral pressure = 95 pcf* triangular distribution • Allowable Bearing Pressure = 2,000 psf** ' • Unit weight of soil cover = 125 pcf * Assumes full hydrostatic head and at-rest pressure conditions. 1 "Assumes subgrade prepared as recommended in "Site Preparation and Structural Fill" section of this report. iPipe Anchorage Considerations Special considerations needed to be taken for a pipe outfall laid on a slope include providing an ' adequate connection to the wall of the catch basin and providing restraint against lateral movement. Several methods are available for accomplishing these requirements. We recommend that the pipe manufacturer or contractor provide a tensile and shear connection ' detail between the catch basin/drop structure and the outfall pipe which will prevent the pipe from pulling out. Similarly, the wall of the catch basin must be of adequate strength to withstand the loading imposed by the outfall pipe. A typical connection will consist of a flange ' adaptor with a grooved lip and a two piece steel clamp mortared into the catch basin. We recommend that the HDPE pipe be anchored at each joint, typically every 40 feet. A typical anchorage would consist of a pipe collar pinned to the slope with rebar or some other form of metal spike. CLOSURE The conclusions and recommendations presented in this report are based on the explorations accomplished for this study and our understanding of the project at this time. The number, locations, and depths of the explorations were completed within the site and work scope constraints so as to yield the information needed to formulate our recommendations. AGRA Earth & Environmental, Inc. would be available to provide geotechnical engineering services during the construction phase of this project. In the event that variations in the subsurface conditions are observed at the time, we would be available to provide additional geotechnical recommendations to minimize delays as the project develops. ' L,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 11 We trust that this report serves your immediate needs. We appreciate the opportunity to provide these services. If you should have any questions, or need additional information, please do not hesitate to call at your convenience. 1 Respectfully submitted, AGRA Earth & Environmental, Inc. ' Curt R. Thompson Senior Project Geo gist ~ `JLA <t1` v Benjamin eiss, P.E. ' Senior Project Engineer EXPIRES _ .15/2/ ,F �� cz John E. Zipper, P.E. GI3TB4 ti� Senior Associate ��`SIONALS Enclosures: Figure 1 - Location Map EXPIRES 1 /24/q-7 Figure 2 - Site and Exploration Plan, Outfall Figure 3 - Geologic Profile Figure 4 - Site and Exploration Plan, Outlet Structure Appendix A - Subsurface Exploration Logs Appendix B - Laboratory Test Procedures and Results ' ,AGRA Earth & Environmental 1--- I 6111 ST i �y no _� u ti3frt sr i a r�.I.0 }� xf ar ME �Y16-c*ST YIAOfOt .o.� r ` TEaF M j� Sr '.e �`'•It. NE ■$Ie I� :1 ��< N ITH $ ST •FF ,1t1 NE IY C� 4 am� Is li T ` T f >-y uo0 : l o .. � W ' S1_ �IY11� " W ' EE O \� _ �• wl 6T 'i 05F l A - < _- afOai f 7Ap 9p f� I i�'• N Al �R7 MY '. i N Y' ,� I32N0 1 ST _ s nl sT rn s \ •,7 n NE yam. NE TILLICIAI 8 •ST t S i081N ST ST N , �� CTH S<VICTp6TAl < Ko rr J 17# Y LEISLRE 13`rM l u r ST 18 aENrav "` " , NOW 16 ESTATES S 2ND� s^ Era. J aacrcar PANX e >w A '�Y ' •Es �A r ,� : � er• •� S 3RD r S tl � ���•. ; g UIRS 0� �y, s '�ITH " �' S sr` � � �� A•s j 19A�F ». 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DRAWING NO. 11 10496-01 LOCATION.DWG TOP / OF SLOPE ' LANDSCAPE BARK AND PLANTINGS LANDSCAPE I' REFLECTOR TIMBERS \ SIGNS 12" CMP OUTFACE GRAVEL HIGH — --._ UNDERGROUND AVENUE � DRAINAGE PIPE SOUTH DRAINAGE CHANNEL J B—1 ASPHALT 1 — DRIVEWAY SPRINKLER / HEAD BRICK I GRASS r Z Icia ➢'j 00 N L I po 1 '525 \ HIGH LEGEND AVENUE SOUTH iB-1 BORING NUMBER AND TOP APPROXIMATE LOCATION OF SLOPE 0 20 40 DRAWING BASED ON CITY OF RENTON, DEPARTMENT OF PUBLIC WORKS SCALE IN FEET PLAN WTR 27-2028. FIGURE 2 W.O. 11-10496-01 HIGH AVENUE SOUTH OUTFALL W AG R A DESIGN CRT RENTON, WASHINGTON Earth &Environmental DRAWN JMR 11335 N.E. 122nd Way, Suite 100 DATE JAN 1996 SITE PLAN Kirkland, WA, U.S.A. 98034-6918 SCALE 1"=20' ' AGRA EARTH do ENVIRONMENTAL, INC. DRAWING NO. 11 10496 SITE.DWG CMP backfill - slope fill - Very loose to loose, 340 silty SAND with some gravel to gravelly CATCH BASIN 340 Qit - Recessional kame terrace 12" CMP deposits - Loose to medium B-1 ' dense SAND - gravelly SAND — ———— ——— 320 Fill—_ 2 - — �` 320 Qit — - '' ' Qu -undifferentiated Till Very stiif to hard, _ _ _ — layers and interbedded Glacilfluvial SAND - sandy SILT to silty SAND 16 300 gravelly SAND Qu 26 300 32 _ ? 34 — Quarry spoils 280 on surface — _ Qu _ 280 Medium dense to dense, SAND - gravelly SAND Qu - Dense, silty SAND - - - - - - - - - - - - - -? 260 SANDSTONE 260 W i L-i Z 240 LEGEND 240 Z Renton Formation (Tr) O — -- — — Q INTERFACE LINE > 220 — — _? 220 J — — — COAL 9 ' Lv — — — COAL a' d SILTSTONE ® DEBRIS _ _ _ _ _ COAL 200 Debris Dam — — _ SILTSTuN_E ? 200 Debris Dam SANDSTONE trees and soil - Quarry spoils and trees B_1 BORING NUMBER AND accumulated sands, silts APPROXIMATE LOCATION graves from upsope 18O l f l 34 I STANDARD PENETRATION TEST 180 - BLOWS PER FOOT 160 — — — — — — — — —? 160 NOTE: THE STRATA ARE BASED UPON SILTSTONE INTERPOLATION OF OUR TEST BORING AND FIELD RECONNAISSANCE AND PUBLISHED GEOLOGIC LITERATURE AND MAY 140 NOT REPRESENT ACTUAL 140 — — — — — _ SUBSURFACE CONDITIONS. SANDSTONE - SILTSTONE - COAL SEAM 120 120 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 —20 —40 —60 —70 —80 —100 DISTANCE IN FEET ALONG OF PROFILE FIGURE 3 W.O. 11-10496-01 HIGH AVENUE SOUTH OUTFALL *At3 R A DESIGN CRT RENTON, WASHINGTON Earth &Environmental DRAWN JMR 11335 N.E. 122nd Way, Suite 100 DATE JAN 1996 GROUND SURFACE GEOLOGIC PROFILE Kirkland, WA, U.S.A. 98034-6918 SCALE 1"=30' AGRA EARTH do ENVIRONMENTAL, INC. DRAWING N0. 11 10496 X—S—A.OWG O o �O� Pro- TP--5 g Y ' 0 20 40 �-- SCALE IN FEET w TP-3 c DRAINAGE... PATH 120 OUTLET STRUCTURE TPP--2 / T;�-4 1 "Jo I Aso 1140 TP�1 NEW 12" SHDPE PIPE ' 4e/ LEGEND i Aso TP�-5 TEST PIT NUMBER AND p� APPROXIMATE LOCATION � OQ U C FIGURE 4 W.O. 11-1Q496-01 HIGH AVENUE OUTFALL * AG R A DESIGN CRT _ RENTON, WASHINGTON Earth & Environmental DRAWN DMW w 11335 NE 122nd Way, Suite 100 DATE MAY 1996 SITE & EXPLORATION PLAN ' a Kirkland, Washington, U.S.A. 98034-6918 OUTLET STRUCTURE cl SCALE 1"=20' a Appendix A 1 1 1 1 1 APPENDIX A 1 SUBSURFACE EXPLORATION PROCEDURES AND LOGS 11-10496-01 1 1 1 1 1 i 1 1 1 1 ,AG RA Earth & Environmental APPENDIX A 1 1-1 0496-01 SUBSURFACE EXPLORATION The field exploration program conducted for this study consisted of advancing one hollow-stem auger test boring and excavating five test pits. The exploration locations were obtained in the field by pacing from site features shown on a site map provided us. The approximate locations of our explorations are indicated on the Site and Exploration Plan, Figure 2. The locations of the explorations should be considered accurate only to the degree implied by the method used. ' Hollow-Stem Auger Boring The test boring was drilled by a local exploration drilling company under subcontract to our firm on 16 January 1996. The boring consisted of advancing a 4% inside diameter (ID) hollow-stem ' auger with a truck-mounted CME 85 drill rig. During the drilling process, samples were obtained at generally 2.5 to 5.0 foot depth intervals. The borings were continuously observed and logged by an engineering geologist from our firm. Disturbed samples were obtained b using the Standard Penetration Test procedures as P Y 9 described in ASTM:D 1586. This test and sampling method consist of driving a standard 2-inch outside diameter split barrel sampler a distance of 18 inches into the soil with a 140 pound hammer free-falling a distance of 30 inches. The number of blows for each 6-inch interval is recorded. The number of blows required to drive the sampler the final 12 inches is considered the Standard Penetration Resistance ("N") or blow count. The blow count is presented graphically on the boring logs in this appendix. If a total of 50 blow is recorded within one 6- inch interval, the blow count is recorded as 50 blows for the number of inches of penetration. The resistance, or "N" value, provides a measure of relative density or granular soils or the relative consistency of cohesive soils. The soil samples obtained from the split-barrel sampler were classified in the field and representative potions were placed in plastic containers. The samples were then transported ' to our laboratory for further visual classification and laboratory testing. Samples are generally saved for a period of 30 days unless special arrangements are made. ' The boring log presented in this appendix is based on the drilling action, inspection of the samples secured, laboratory results, and the field log. The various types of soils are indicated, as well as the depths where the soils or characteristics of the soils changed. It should be noted that these changes may have been gradational, and if the changes occurred between sample intervals, they were inferred. rThe groundwater conditions observed during the exploration program are indicated on the boring or test pit logs, where appropriate. The subsurface water conditions were evaluated by ' observing the free water on the sampling rods for the boring explorations and moisture conditions of the samples and side walls for the test pits. The groundwater level is indicated on the boring logs by a triangular symbol and the designation "ATD" (At Time of Drilling). The groundwater depth shown on the boring log is generally indicative of the open water level in ' ,AG RA Earth & Environmental the boring at the time the boring was advanced, but does not necessarily represent the true regional groundwater table. Test Pit Excavations ' Five test pits were excavated on 15 January 1996 with a track-mounted backhoe operated by a local excavation contractor. Each test pit was continuously logged and observed by one of our experienced engineering geologists. In-situ strength and quality attributes of materials encountered in the test pits were estimated by our field observer based on experience with similar soils and on the difficulty incurred during excavation. Disturbed, but representative, samples of the soils in the test pits were retrieved, classified in the field, and transported in plastic containers to our laboratory for further evaluation and classification. The test pit logs presented in this appendix are based on inspection of the soil samples and the field logs. ' ,AG R A Earth & Environmental PROJECT: High Avenue South Outfall wo. 17- 70496-01 BORING NO. B-7 SOIL DESCRIPTION PENETRATION RESISTANCE Page 1 A, Location: See Site Plan IL of 2 Standard Blows per foot Other Approximate ground surface elevation: 326 feet V) V) 0 1 1 0 0 10 20 30 40 50 TESTING Crushed Rock(Fill) NIE -—————————————————————————————- ------- Very loose,moist,brown,silty,gravelly SAND with some organics(Fill) ------- -------............................ ------- ....... ------- ------- -------........................... ........ ................ S-1 ................ ---- --------------- ............... ....... -—————————————————————————————- 5 Loose,moist,brown,fine to medium SAND with some coarse sand,trace gravel,silt and organics S-2 -------- ............... .............................. ....... ....... ..... . ..... ...... ......... ............... .............................. ....... ............ ................ ...................................... ....... ....... S-3 ............. ............................ ....... - 10 -—————————————————————————————- Very stiff to hard,moist,brown,sandy SILT with S-4 ................. ------- ------- ....... ------- trace to some gravel and Interbedded oxidized orange,fine to medium SAND(114'- 112'zones) ........ ...............------- ............... --------------- ................ ............... ------------I ....... ....... S-5 ........... .......................... .. .................... 15 S-6 -­ ---------­­---------------------- ------- ---- - -- --—————————————————————————————- ............................ ....... ....................... Very stlff,moist,brown/gray,sandy SILT with some gravel -------- ....... ................. --------------...............­ S-7 .............. .....................J....... ............... 20 - ------- ......................------------ ------- ....... ........... ............... ....... ............... Grades with some clay,trace gravel -------- ....... ....... ...................................... ............... S-8 ..................:......... -------- ....... ............... 25 .. ............. ........ ... . :.... ............................. Hard,moist to wet,brown/gray,sandy SILT with some gravel and Interbedded oxidized orange, .................--------------........ ............. ................ fine to medium SAND(114'- 112'zones) .......................... ----------------- .......... --------------- S-9 ............ ----------------------- ... ­ .............. ....... ...----------- (continued) 30 - 0 20 40 60 so 1 1 00 LEGEND MOISTURE CONTENT E C Plastic limit Natural Liquid limit 2 = 2.00-inch OD split-spoon sample Grain size analysis > C W L& 'S AG R A Earth & Environmental �8 NIE No groundwater encountered W 11335 NE 122nd Way,Suite 100 Kirkland,Washington 98034-6918 < Drilling method: HSA Hammer type: Automatic Date drilled: 16 January 1996 Logged by: CRT PROJECT: High Avenue South Outfoll w.o. 11- 10496-01 BORING NO. B- I _ SOIL DESCRIPTION u� a PENETRATION RESISTANCE Page 2 w Location: See Site Plan w A of 2 Ll v < C 3 Standard Blows per foot Other ' Approximate ground surface elevation: 326 feet a 30 o 10 20 30 ao 50 TESTING Some as above N/E ——————————— —————————————— --------:................;...........................-. ------ ... _ .. Dense,moist,brown,fine to medium SAND with trace coarse sand,gravel and slit -------------- ----------- >-----. -------'--...... S-10 ..........=.......•------ --------....... ---- ........ -- --- -------+..............:.............. ...- . 35 =------- -------= ------------- ------------ ------- ....... ------- Grades with coarser SAND,some gravel to ' gravelly <--------------------- - --=------- .......=....... S-11 Boring terminated at approximately 40 39 feet -- -- ----- ........ --- --- -...... s-... --- 45 ----- --------- ---- --- ------- -----------------------............... ----------------- ------------------ -- -........................ 50 ---------------- .. . .--- ---I-- ... ... ... ........ ....... ....... .................... 55 _ ,------------- ----- ----- ---- ---- 60 0 20 40 so so 100 MOISTURE CONTENT LEGEND c Plastic limit Natural Liquid limit 2 I 2.00-inch OD split-spoon sample ® Grain size analysis imr AG R A Earth & Environmental w N/E No groundwater encountered 11335 NE 122nd Way,Sulte 100 Kirkland,Washington 98034-6918 a Drilling method: HSA Hammer type: Automatic Date drilled: 16 January 1996 Logged by: CRT TEST PIT LOGS 11-10496-01 Depth (feet) Material Description Test Pit TP-1 Location: See Site Plan Approximate ground surface elevation: Unknown ' 0.0 - 3.0 Forest duff atop very loose, moist to wet, dark brown, silty SAND to sandy SILT with some organics, gravel, coal, brick fragments and substantial roots (Fill and/or Colluvium). 3.0 - 10.0 Loose to medium dense, wet, brown/gray, silty SAND with some gravel, coal and wood fragments (Fill and/or Colluvium). 1 10.0 - 13.0 Medium dense, moist to wet, tan-brown, silty SAND with some gravel (Weathered Sandstone). ' Test pit terminated at approximately 13.0 feet Severe caving at 0 to 10.0 feet Slow seepage at 3.0 feet Moderate seepage at 10.0 feet i Test Pit TP-2 Location: See Site Plan Approximate ground surface elevation: Unknown ' 0.0 - 2.5 Forest duff atop soft, moist to wet, black, sandy SILT with some organics, gravel and substantial roots (Fill and/or ' Colluvium). 2.5 - 9.0 Loose to medium dense, wet, brown, silty SAND with some gravel, coal and wood fragments (Fill and/or Colluvium). 9.0 - 1 1 .0 Medium dense, wet, blue-gray, silty SAND with some gravel. Test pit terminated at approximately 11.0 feet Severe caving from 0 to 9.0 feet Moderate seepage at 3.5 feet Rapid seepage at 9.0 feet 1 1-1 0496-01 Test Pit Log, Page 2 Depth (feet) Material Description Test Pit TP-3 Location: See Site Plan Approximate ground surface elevation: Unknown 0.0 - 1.5 Forest duff atop very loose, moist to wet, brown-gray-black, silty SAND with some organics, gravel and substantial roots (Fill and/or Colluvium). 1.5 - 10.0 Loose, wet, brown-gray-black, gravelly, silty SAND with some wood, coal, and moderate roots to 3.0 feet (Fill and/or Colluvium). ' 10.0 - 12.0 Medium dense, wet, gray, silty SAND with some gravel and interbedded sandy SILT. Test pit terminated at approximately 12.0 feet ' Moderate to Severe caving 0 to 10 feet Rapid seepage at 5.0 feet Test Pit TP-4 Location: See Site Plan Approximate ground surface elevation: Unknown ' 0.0 - 3.0 Forest duff atop very soft, wet, brown, sandy SILT with some clay, wood debris including timbers, trace gravel, and moderate 1 roots (Fill and/or Colluvium). 3.0 - 8.0 Soft, wet, brown-gray, sandy SILT with some clay, brick, and coal fragments and wood debris including timbers (Fill and/or Colluvium). Test pit terminated at approximately 8.0 feet Severe caving 0 to 8.0 feet, requires stoppage due to caving conditions Moderate surficial seepage Rapid seepage at 1 .5 feet 1 1-1 0496-01 Test Pit Log, Page 3 ' Death (feet) Material Description Test Pit TP-5 ' Location: See Site Plan Approximate ground surface elevation: Unknown 0.0 - 1 .5 Forest duff atop very loose, wet, black, silty SAND to sandy SILT with some organics, trace gravel and substantial roots (Fill and/or Colluvium). 1.5 - 3.0 Loose, wet, brown-gray, silty, gravelly SAND with some organics and substantial roots (Fill and/or Colluvium). 3.0 - 8.0 Loose, saturated, brown-gray, silty SAND with some gravel, logs, wood debris and coal (Fill and/or Colluvium). 8.0 - 10.0 Medium dense, wet, blue-gray, silty SAND with some gravel. ' Test pit terminated at approximately 10.0 feet Severe caving 0 to 8.0 feet Rapid seepage at 3.0 feet Date excavated: 15 January 1996 Logged by: CRT 1 1 1 Appendix B APPENDIX B LABORATORY PROCEDURES AND RESULTS 11-10496-01 ' , AGRA Earth & Environmental APPENDIX B 1 11-10496-01 LABORATORY TESTING PROCEDURES A series of laboratory tests were performed during the course of this study to evaluate the index and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests performed are given below. Visual Classification 1 Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in watertight containers and transported to our laboratory where the filed classifications were ' verified or modified as required. Visual classification was generally done in accordance with the Unified Soil Classification system. Visual soil classification includes evaluation of color, relative moisture content, soil type based on grain size, and accessory soil types included in the 1 sample. Soil classifications are presented on the boring and test pit logs in Appendix A. Moisture Content Determinations ' Moisture content determinations were performed on representative samples obtained from the explorations in order to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM:D-2216. The ' results of the tests are listed in this Appendix and presented on the boring log in Appendix A. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. A grain size analysis was performed on representative samples in general accordance 1 with ASTM:D-422. The results of the grain size determination for the samples were used in classification of the soils, and is presented in this Appendix. ,AG RA Earth & Environmental MOISTURE CONTENT 1 Job Name: High Ave. South Outfall Job Number: 1 1-1 0496-01 Date: 1-17-96 Exploration: B-1 B-1 B-1 B-1 B-1 B-1 TP-1 TP-2 TP-2 TP-3 Sample Number: S-1 S-2 S-6 S-8 S-9 S-11 Depth: 2.5' 5.9 15.9 22.5' 27.5' 37.5' 3.0-10.9 0.0-2.5' 2.5-9.9 0.0-1.5' Wet weight: Dia. of sample: Length of Sample: Volume (cf): Wet Density: 1 Dry Density: Wet sample +tare: 347 475 538 424 607 651 714 492 586 692 Dry sample+tare: 335 458 500 375 528 637 645 419 532 619 Water: 12 18 38 49 79 14 69 73 54 73 Tare: 161 162 162 169 162 161 167 155 165 167 Moisture Content: 7% 6% 11% 24% 22% 3% 14% 27% 15% 16% IExploration: TP-3 TP-4 TP-4 Sample Number: ' Depth: 10.0-12.0' 0.0-3.0' 3.0-8.0' Wet weight: Dia. of sample: Length of Sample: ' Volume (cf): Wet Density: Dry Density: Wet sample +tare: 725 664 646 Dry sample+tare: 637 541 523 Water: 88 123 123 0 0 0 0 0 0 0 Tare: 167 163 155 Moisture Content: 19% 33% 33% Exploration: Sample Number: Depth: Wet weight: 1 Dia. of sample: Length of Sample: Volume (cf): Wet Density: Dry Density: Wet sample +tare: ' Dry sample+tare: Water: 0 0 0 0 0 0 0 0 0 0 Tare: Moisture Content: GRAIN SIZE DISTRIBUTION SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER 36' 12" 6" 3" 1 1/2" 3/4" 3/8" 4 10 20 40 60 100 200 100 s0 i 80 1 70 1 } m W � 1 W �° U ' W 30 a 20 i 10 o 1000.00 100.00 10.00 1.00 0.10 0.01 0.00 GRAIN SIZE IN MILLIMETERS Coarse Fine Coarse Medium Fine Silt Clay BOULDER,5 COBOL wo FINE GRNNED Exploration Sample Depth Moisture Fines Soil Description -f F� B-1 S-3 7.5' 8% 2% SAND,trace silt •-�-�-�-+ B-1 S-4 10.0' 15% 48% Sandy SILT,trace gravel TP-3 1.5-10.0' 27% 32% Gravelly Silty SAND ' Project: High Ave South OutFall WorkOrder: 11-10496-01 *AGRA Earth & Environmental Date: 1-17-96 11335 NE 122nd Way Suite 100 Kirkland, Washington 98034-6918 * AGRA AGRA Earth& Environmental, Inc. Earth & Environmental 11333 NE 122nd Way Suite 100 Kirkland. Washington U.S.A. 98034-6918 Tel (206) 820-4669 Fax (206) 821-3914 15 May 1996 1 1-1 0496-01 City of Renton Planning/Building/Public Works Department Municipal Building 200 Mill Avenue South ' Renton, Washington 98055 Attention: Mr. Ronald J. Straka, P.E. Engineering Supervisor Subject: Subsurface Exploration and Geotechnical Engineering Study ' High Avenue South Outfall 525 High Avenue South ' Renton, Washington Gentlemen: This report presents the results of our subsurface exploration and geotechnical engineering study for the above referenced project. The purpose of this study was to interpret general surface and subsurface site conditions from which we could formulate a summary discussion regarding general site stability, temporary open cut slope and shoring considerations, and soil design parameters for the excavation and replacement of the upslope storm water catch basin ' and piping. Recommendations regarding support for the proposed High Density Polyethylene (HDPE) piping down the slope to the concrete energy dissipator/diffusion structure are also discussed. 1 Our scope of services consisted of a visual site reconnaissance, subsurface exploration, laboratory testing, geotechnical analysis, and preparation of this report. Our work has been performed in accordance with our scope of geotechnical services dated 14 November 1995 and our on-call consultant contract with the City of Renton. Authorization to proceed with this study was granted by the City of Renton on 4 January 1996. This report has been prepared 1 for the exclusive use of the City of Renton, and their agents for specific application to this project in accordance with generally accepted geotechnical engineering practices. ISITE AND PROJECT DESCRIPTION The storm drain outfall is located at the north end of High Avenue South, northeast of a residence located at 525 High Avenue South in Renton, Washington. The storm drain outfall Engineering& Environmental Services City of Renton 1 1-1 0496-01 15 May 1996 Page 2 is a 12-inch diameter corrugated metal pipe (CMP) which serves as the discharge for the collected upland surface water. The nearest catch basin for the CMP is approximately 75 feet south of the top of slope and 90 feet south of the outfall. The storm water discharges from the pipe near the top of the slope and follows a drainage channel steeply downslope. ' We performed a preliminary eotechnical memorandum in late August 1995 to assess impacts P P Y9 9 ' to the storm drain line and future slope stability after a landslide occurred following heavy rains on 16 August 1995. Additional observations on 9 October 1995 disclosed substantial channel cutting and loss of bank soils in the discharge area compared to our 31 August 1995 geologic ' reconnaissance. The City of Renton performed temporary erosion control measures in mid October 1995 including a tightline extension to the outfall pipe, and placement of geotextile fabric atop the upper exposed slope soils and below the tightline pipe. ' We understand the City of Renton plans to reconstruct the existing outfall with a HDPE tightline. A new upslope catch basin inlet manhole will replace the existing catch basin and ' serve as the start of the HDPE tightline. The HDPE tightline will exit the catch basin at a depth of approximately 10 to 15 feet below the top of slope and then continue atop the surface of the drainage channel to its terminus at a new downslope energy dissipator/diffusion structure. In the event of any changes in the nature or design of this project, the conclusions and recommendations contained in this study should be reviewed and modified, as necessary, to reflect the changes. SITE CONDITIONS The site conditions were evaluated for this study in August and October 1995, and January 1996. The surface and subsurface conditions are described below, while the exploration procedures and interpretive logs of the explorations are presented in Appendix A. The general ' project vicinity is shown on the Location Map, Figure 1. The approximate locations of the explorations are indicated on the Site and Exploration Plan, Figures 2 and 4. Laboratory ' procedures and test results are presented in Appendix B and on the exploration logs, where appropriate. Surface Conditions The site is located at the north end of High Avenue South, northeast of the residence located at 525 High Avenue South, in Renton, Washington. The upslope area includes a catch basin ' within the asphalt roadway/driveway, a gravel parking area, a landscaping berm including beauty bark and plantings and grass covered areas. The eroded slope area adjacent to the existing outfall pipe where landsliding has occurred is approximately 35 to 40 feet in width and 1 25 to 30 feet in height. In mid October 1995, the City of Renton extended the outfall pipe further downslope and placed geotextile fabric atop the upper exposed slope and below the tightline pipe extension to reduce further erosion. L, AG R A Earth & Environmental 1 City of Renton 1 1-1 0496-01 15 May 1996 Page 3 The drainage channel below the outfall was surficially covered with quarry spall rock (4- to 8- inch) in the splash area and a limited area further downslope. The slopes adjacent to the drainage channel were generally covered with surface brush, blackberries, and small alder and maple trees. The trees on the slope have been regularly topped for the downtown view to the northwest. A 10- to 20-foot high pile of accumulated trees, root mass, brush, soil, quarry spall rock, and ' debris including concrete and CMP is located at the base of the upper slope within the drainage channel. The debris pile is on the order of 60 feet in length. A smaller debris pile consisting ' of finer debris, wood, and soil is located downslope of the large debris dam. An alluvial fan type soil deposit is located below the debris piles in the area of the proposed energy dissipator/diffusion structure. The topography becomes less severe in this area where soil is ' deposited during outfall runoff. Further downstream, the drainage channel cuts through waste piles of coal, siltstone, and sandstone to pond at the base of the slope in the proposed City of Renton park site. During a heavy rain event, we observed that the runoff drained to a catch basin at the northwest area of the proposed park. Subsurface Conditions To assess subsurface conditions we performed an exploration program including one test boring at the top of the slope and five trackhoe excavated test pits in the area of the proposed energy dissipator/diffusion structure near the bottom of the slope. The test boring disclosed approximately 4.5 feet of fill soils consisting of a very loose to loose silty gravelly sand with some organics atop a recessional deposit consisting of loose sand with trace gravel, silt and organics. At a depth of approximately 10.5 feet to 31 feet, we encountered a very stiff to hard sandy silt with some gravel and interbedded sand. A dense sand with trace gravel and silt was encountered at approximately 31 feet in depth and graded to gravelly at 36 feet to the total depth of the boring at 39 feet. Below the recessional deposits at 10.5 feet, the soils are classified as undifferentiated deposits which include three or more glacial till sheets, glaciofluvial sand and gravel, glaciolacustrine clay and sand, and non- glacial sand, clay, and thin peat. The trackhoe excavated test pits in the area of the proposed energy dissipator/diffusion ' structure disclosed approximately 8 to 10 feet of fill and/or colluvium consisting of a loose, silty sand to sandy silt with some gravel to gravelly and coal, wood, and brick fragments. Native, medium dense silty sand with some gravel was typically encountered below the upper loose ' soils in the test pits. Moderate to severe caving of the test pit walls was observed within the fill soils. Test pit TP-4 encountered wood timbers within the fill soils. It would appear that the fill and/or colluvium encountered in the test pits is related to mining of resources of coal and siltstone from the site area. A brick manufacturing company existed downslope at the ' ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 ' 15 May 1996 Page 4 proposed park site, which mined the siltstone (shale) for brick manufacturing. As mining of ' resources was conducted, the spoils remained at the base of the slope. Though our test pit explorations were limited, areas of mounded spoils, and disturbance to the area was observed across the lower slope areas. In addition, downslope movement of surficial soils including slumps (colluvium) were observed in the lower slope area of the project site. Groundwater was not observed in our test boring at the top of the slope, but was observed as moderate to rapid seepage at depths ranging from about 1.5 to 10 feet in all five test pits at the bottom of the slope. It should be noted that seepage from precipitation may at times ' become "perched" within the fill and/or atop the dense silty sands and hard sandy silts of the undifferentiated deposits in the upper slope area. If perched water is encountered, the proposed outfall design improvements should not require further modification. Please refer to our recommendations in the site preparation, drainage and slope considerations sections of this report as they relate to groundwater seepage. GEOLOGIC RECONNAISSANCE We performed a geologic reconnaissance of the drainage channel slope for our previous study on 31 August 1995. For this study, we performed a ground surface geologic profile of the slope and incorporated our test boring advanced at the top of the slope. We visually observed site conditions and channel soil contacts during our site reconnaissance on 22 January 1996. The topographic information, based on a City of Renton supplied topographic plan, shows a top of slope elevation of approximately 326 feet and 55 feet at the bottom of the slope. The toe of the accumulated upslope debris, spalls, etc. is approximately elevation 160 feet. The proposed energy dissipator manhole structure will be at approximately elevation 140 feet. Presented below is a summary description of the channel soil contacts observed during our site reconnaissance. The existing slope profile and soil contacts are shown on Figure 3, Ground Surface Geologic Profile. Our test boring generally correlated with the exposed soil contacts in the drainage channel. Approximately 5 to 8 feet of very loose, silty, gravelly sand fill was observed atop 5 to 6 feet ' of loose sand with trace gravel. This native sand is mapped as recessional stratified drift, Qit, kame terrace deposits. The Renton Quadrangle Geologic Map, 1965, describes the Kame ' terrace deposits as sand and pebble to cobble gravel in scattered terraces whose surfaces locally are deformed by extensive collapse. The fill and recessional soils have formed a near vertical slope (.5 Horizontal:1 Vertical) from the top of slope to approximately 5 feet below the outfall in the drainage channel. Below the recessional deposits and approximately 5 feet vertically below the outfall pipe, we observed a 15-foot near vertical slope of glacially consolidated, very stiff to hard sandy silt with some gravel, mapped as Qu, undifferentiated deposits. The undifferentiated deposits include three or more till sheets, glaciofluvial sand and gravel, glaciolacustrine clay and sand, and non-glacial sand, clay, and thin peat. ' L,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 5 We observed Qu deposits of interbedded silty sands, sandy silts, and gravelly sands in our test ' boring and along the drainage channel and banks for approximately 60 feet on a slope on the order of 1 H:1 V (Horizontal:Vertical). Our test boring encountered a sand interbed of the Qu deposit from approximately 31 feet to the boring bottom depth of 39 feet. Though not encountered in the test boring, the sandstone (which is mapped as the Renton Formation Jr)) was observed in the drainage channel approximately 60 feet downslope from the base of the near vertical slope below the outfall. A layer of quarry spall rock (4 to 8 inches in size) and geotextile fabric covers the upper drainage channel below the outfall to approximately the sandstone contact. The Renton Formation consists of arkosic sandstone, mudstone, shale, and coal beds. This formation is characterized by numerous faults of small displacement, wavy bedding, and a thickness of ' approximately 2,500 feet. The coal and shale (siltstone) from this formation was mined extensively in Renton, including beneath the project area. The observed upper sandstone forms a 1 H:1 V slope (similar to the Qu deposits) for approximately 15 feet and then drops vertically approximately 20 feet. The sandstone in the drainage channel has formed steps with interbedded coal and siltstone for approximately 100 feet. The steps form an overall slope on the order of 1.25H:1 V. 1 A 10- to 20-foot high pile of accumulated trees, root mass, brush, soil, quarry spall rock, and debris including concrete and CMP is located at the base of the upper slope at approximately I elevation 165 feet. The debris pile is on the order of 60 feet in length. A smaller debris pile consisting of finer debris, wood, and soil is located downslope of the large debris dam. A siltstone horizon of the Renton Formation was observed beneath the debris piles. Further. ' downslope, we observed interbedded sandstone, siltstone, and coal along the drainage channel. In the area of the proposed energy dissipator manhole structure, an alluvial fan type soil deposit 1 is located where the topography becomes less severe. The runoff channel in this area deposits sediment rather than downcutting a deeper channel. Downslope movement of surficial soils including slumps and/or colluvium are evident in the lower areas of the channel. The lower Lareas also contain fill, as observed in our test pits, which relate to the mining of the siltstone and coal from the area. ' Groundwater seepage from the upper slope was not evident during our site reconnaissance. We observed surficial seepage in the area of the test pits in the lower slope area. Refer to the ' test pit logs for noted surficial seepage and depths of observed seepage. CONCLUSIONS AND RECOMMENDATIONS ' Development plans call for removal of the existing catch basin structure on High Avenue South and the approximately 90 feet of existing corrugated metal pipe (CMP) to the north. Replacement with a new concrete manhole and 12-inch diameter high density polyethylene (HDPE) pipe is planned. The HDPE pipe will tightline the storm water down the surface of the ' L,AGRA Earth & Environmental 1 City of Renton 1 1-1 0496-01 15 May 1996 Page 6 slope to an energy dissipator/diffusion structure near the base of the slope. The proposed ' energy dissipator/diffusion structure will be a 54 to 72 inch diameter partially buried manhole structure where the HDPE tightline will enter near the ground surface. The outlet pipe from the structure will be higher than the inlet to dissipate the energy of the storm water. ' Improvements to the storm water outfall are necessary to lessen the erosion and downcutting of the drainage channel in the upper slope area and possible damage to the existing CMP outfall. Site Preparation and Structural Fill ' Based on our test boring, the top of slope area at the boring location consists of approximately 4.5 feet of very loose to loose silty, gravelly sand fill atop approximately 6 feet of loose sand (recessional deposits). At 10.5 feet in depth to approximately 31 feet, a very stiff to hard sandy silt interbedded with sand was encountered. A majority of the excavation for the new upper catch basin manhole and HDPE pipe, planned at a depth of approximately 10 to 15 feet below existing grade, will encounter the existing fill soils, loose recessional sands, and possibly the very stiff to hard sandy silts. The exposed subgrade surface for the catch basin structure should be free of loose/disturbed soil or standing water and compacted such that an in-place soil density of at least 90 percent is achieved to a depth of 12 inches, using the ASTM:D-1557 modified Proctor maximum dry density. We recommend a bedding material for the catch basin suitable for rigid pipe consisting of crushed, partially crushed, or naturally occurring granular material free from wood waste and organic material and having a maximum dimension of 1 inch. The bedding material should conform to the gradation described in Section 9-03.15 of the 1994 WSDOT/APWA Standard Specifications. If any organic or unsuitable soils are ' encountered at the proposed pipeline subgrade, overexcavation to expose suitable competent material would be necessary. Backfill should consist of compacted Class A, Class B, or Class C Foundation Material as described in Sections 9-03.17 and 9-03.18 of WSDOT/APWA Standard Specifications. Controlled Density Fill (CDF) or lean concrete may be used as an alternate foundation and backfill material. According to manufacturer specifications, no bedding material is required below HDPE pipe. To prevent migration of water within the bedding material or backfill and potential of sloughing of the slope during compaction, use of CDF within 30 feet behind the slope is recommended in lieu of a permeable granular bedding material. Alternatively, the use of low permeability pipe collars, such as CDF, clay/bentonite or concrete collars/check dams could be installed at several locations along the buried HDPE tightline. The pipe collar should fully envelope the pipe and ' extend a minimum of 1-foot below the base of the trench and 1 foot above the top of the pipe bedding. We anticipate that pipe collars on the order of 3 to 4 feet in length should be ' adequate. As previously mentioned, roughly 10 feet of loose fill with debris was encountered at the ' proposed downslope energy dissipator location. It will likely not be practical to overexcavate ' L,AGRA Earth & Environmental ' City of Renton 1 1-1 0496-01 15 May 1996 Page 7 and replace all the existing fill beneath the energy dissipator structure. Therefore, it is our opinion that overexcavation of 3 feet of unsuitable soils be performed below the structure. Due to the presence of groundwater and poor ground conditions, we recommend that quarry spalls be used as foundation backfill material for the 3 feet under the structure. The quarry spalls should be firmly seated into the underlying ground using the bucket of the excavator. We recommend that the quarry spall foundation mat extend laterally at least 2 feet beyond all sides of the energy dissipator structure. A limited length, on the order of 30 to 40 feet of HDPE pipe will be buried in the downslope pipe trench as it connects to the outlet structure. The depth of burial will vary from ' approximately 1 to 4 feet and bedding material is not required below the HDPE pipe. The suitability of soils for structural fill use depends primarily on the gradation and moisture ' content of the soil when it is placed. Soil to be used as structural fill should be free of organics and other deleterious material. As the amount of fines (that portion passing the U.S. No. 200 ' Sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. Soil containing more than about 5 percent fines by weight usually cannot be compacted to a firm, non-yielding conditions when the moisture content is more than about 2 percent above optimum. We anticipate that the on-site soils for the High Avenue work that would be available for fill as a result of trench excavation would primarily be a silty gravelly sand with some organics (old fill) and a sand with trace gravel, silt and organics. The soils disclosed in the test pits near the proposed energy dissipator location consist of loose silty sand with some gravel, wood, coal and organics (fill and/or colluvium) to a depth of approximately 10 feet. It should be realized that the on-site soils are moisture-sensitive and may be difficult or impossible to use as structural fill during wet weather or under wet site conditions. If rain were to occur while silty 1 soils are exposed, or during their placement, the exposed material should be allowed to sufficiently dry prior to additional filling, as necessary to facilitate compaction. It may be necessary to scarify the upper layer, allow it to dry, and recompact prior to additional filling. It may be necessary to overexcavate and remove wet soils if it is not practical to dry and recompact them. Select "clean" granular soils would then be required for structural fill use. Select imported fill should consist of "clean" free draining, well graded sand and gravel as specified in WSDOT/APWA Section 9-03.19, "Bank Run Gravel for Trench Backfill". Imported fill soils should contain no more than 5 percent fines by weight passing through the U.S. No. 200 Sieve when measured against the minus No. 4 fraction. Material of this type may be successfully placed and compacted under a wider variety of weather conditions. Soils used for structural fill should have no particles greater than 2'/2 inches in maximum dimension and be free of organics and other deleterious materials. Structural fill should be placed over a properly prepared subgrade, as discussed above. Structural fill should be placed in 8-inch maximum 1 i ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 8 loose lifts. Each lift should be compacted to at least 90 percent of the laboratory Proctor ' maximum dry density, using ASTM:D-1557 as the standard. Drainage Considerations ' Based on our explorations, groundwater was not encountered in our test boring advanced at the top of slope area, but was encountered in all of the test pits at the base of slope at depths from 0 to 10 feet. The excavations for the proposed structures and pipeline should be ' dewatered as needed prior to placement of structural fill soils, with exception of where quarry spalls are used as foundation material. The soils encountered at the site are silty and could be readily disturbed by traffic when wet. Therefore, we recommend that the contractor take ' precautions to maintain a dry construction site and protect the subgrade from disturbance. The contractor should be prepared to control water seepage from precipitation or groundwater with the use of interceptor trenches or pumped sumps. Surface water should be diverted away from the pipeline and manhole excavations by means of berms, swales, French drains, or sloping of grades away from the construction area. ' Temporary Slope and Shoring Considerations The stability of temporary cut slopes made during the site work is a function of many factors, ' including, but not limited to, the following considerations: 1) the presence and abundance of surface water and groundwater; 2) type and density of the various soil strata; 3) the depth of the cut; 4) surcharge loadings adjacent to the excavation; and 5) the length of time the ' excavation remains open. Consequently, it is exceedingly difficult to establish a safe and maintenance-free cut slope angle in advance of construction. Cut slope stability should, therefore, be the responsibility of the contractor, since he is continuously at the job site, able 1 to observe the nature and condition of the subsurface materials encountered, monitor the cut performance, and control the scheduling of site activities. ' We recommend that excavations greater than 4 feet in vertical height be adequately sloped or braced to prevent injury to workmen from localized sloughing and spalling. All excavations should be accomplished in accordance with applicable local, State, and Federal safety provisions. As recommended in OSHA/WISHA guidelines for Type C soils, cuts in the fill and loose granular native soils should be not steeper than 1.5H:1 V. Under adverse weather conditions, temporary slopes should be draped with Visqueen or other means to protect them ' from the elements and minimize sloughing and erosion. 1 At locations where safe slope angles cannot be accommodated, or in other areas of high groundwater or fill soils, and where sloughing of the excavation sides could endanger either workers, or other features, we recommend that adequate shoring be utilized. We anticipate ' that a steel strutted trench box, braced sheeting, or braced sheet piling could be utilized in any areas where sloughing and/or caving of the trench sidewalls would endanger workers or features adjacent to the trench. Design of trench shoring should be the responsibility of the ' contractor and should be capable of retaining lateral pressures as discussed below. L,AGRA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 9 For the manhole structures, a braced sheeting system would be recommended if safe slope ' angles cannot be accommodated. A "tight" sheeting system would consist of pre-installed steel or timber sheets advanced to approximately 1 to 2 feet below proposed excavation bottom. The sheets would be laterally supported by means of hydraulic cross braces installed at ' designated depth(s) (determined by design) as excavation progresses. In this manner, employees can be protected from cave-in and the risk of collapse of adjacent structures can be minimized. The shoring should be installed in such a manner so as to minimize ground ' vibrations. To this end, an internally braced system would be desirable since a fully cantilevered system would require significant penetration of the sheets into the hard native soils ' to obtain adequate passive resistance; hence, significantly increasing the amount of driving and associated ground vibration. The contractor should be made responsible for the design, installation, and maintenance of an appropriate method of sidewall support for the excavation and any required dewatering. For design of a shoring system with only one level of internal bracing, a triangular active earth ' pressure distribution may be assumed using an equivalent fluid pressure (EFP) value of 47 pounds per cubic foot (pcf). For design of a shoring system with two or more levels of internal bracing, a rectangular active earth pressure distribution with a maximum pressure of 27H ' pounds per square foot (psf) should be used, where H is the height of the excavation, in feet. Alternatively, the shoring may be designed in accordance with WAC 296-155-66105 (or 66103) for Soil Type C. Any alternative shoring systems proposed by the contractor must be ' submitted to the owner and/or his agents for review prior to construction. Permanent Slope Stability Considerations Based upon our site reconnaissance and subsurface explorations, there does not appear to be a deep-seated global stability problem along the alignment of the stormwater outfall. Previous episodes of earth movement appear to be related predominantly to the method of outletting storm water from the upslope catch basin, compounded to a lesser degree by natural surface water runoff from precipitation. Tightlining the outfall as planned should significantly reduce both channel scour and bank erosion/sloughing at the top of the slope. The existing geotextile ' fabric lining at the top of the slope and extension of the CMP outfall further downstream appears to have slowed the erosion process; however, the scarp has still become wider, and can continue to both widen and cut back into the bank of the neighbors property. In order to more aggressively slow down the ongoing bank erosion, we recommend that the oversteepened portion of the bank either be covered with an impermeable plastic membrane or applied with ' a reinforced shotcrete facing. We would be pleased to provide details on either of these methods, or other alternatives at a later time, if requested. ' Design of Buried Structures The following parameters may be used for design of buried structures. We recommend that the detailed design of buried structures be reviewed by AEE as the project proceeds. These ' design parameters should be reviewed based on the structures they are being used for. ,AG RA Earth & Environmental City of Renton 1 1-1 0496-01 15 May 1996 Page 10 • Lateral pressure = 95 pcf* triangular distribution ' • Allowable Bearing Pressure = 2,000 psf* ' • Unit weight of soil cover = 125 pcf * Assumes full hydrostatic head and at-rest pressure conditions. "Assumes subgrade prepared as recommended in "Site Preparation and Structural Fill" section of this report. ' Pipe Anchorage Considerations Special considerations needed to be taken for a pipe outfall laid on a slope include providing an adequate connection to the wall of the catch basin and providing restraint against lateral movement. Several methods are available for accomplishing these requirements. We recommend that the pipe manufacturer or contractor provide a tensile and shear connection ' detail between the catch basin/drop structure and the outfall pipe which will prevent the pipe from pulling out. Similarly, the wall of the catch basin must be of adequate strength to withstand the loading imposed by the outfall pipe. A typical connection will consist of a flange adaptor with a grooved lip and a two piece steel clamp mortared into the catch basin. We recommend that the HDPE pipe be anchored at each joint, typically every 40 feet. A typical anchorage would consist of a pipe collar pinned to the slope with rebar or some other form of ' metal spike. CLOSURE ' The conclusions and recommendations presented in this report are based on the explorations accomplished for this study and our understanding of the project at this time. The number, locations, and depths of the explorations were completed within the site and work scope ' constraints so as to yield the information needed to formulate our recommendations. AGRA Earth & Environmental, Inc. would be available to provide geotechnical engineering services during the construction phase of this project. In the event that variations in the subsurface conditions are observed at the time, we would be available to provide additional geotechnical recommendations to minimize delays as the project develops. t ,AGRA Earth & Environmental 1 City of Renton 1 1-1 0496-01 15 May 1996 Page 11 We trust that this report serves your immediate needs. We appreciate the opportunity to provide these services. If you should have any questions, or need additional information, please do not hesitate to call at your convenience. Respectfully submitted, AGRA Earth & Environmental, Inc. ' Curt R. Thompson Senior Project Geo gist F ; Benjamin pjAeiss, P.E. 1 Senior Project Engineer ' y� ..,` � o� I,F, EXPIRES 10 2 z John E. Zipper, P.E. Senior Associate ONAL A Enclosures: Figure 1 - Location Map EXPIRES 1 /24/ql-= ' Figure 2 - Site and Exploration Plan, Outfall Figure 3 - Geologic Profile Figure 4 - Site and Exploration Plan, Outlet Structure ' Appendix A - Subsurface Exploration Logs Appendix B - Laboratory Test Procedures and Results AG R A Earth & Environmental _ — - ---------- ----- - -- - - - - - - • - - - -- -- --- - - i f -'-sirlw_�La:^4�i .nuL.0 i I.a N ST ST ,.o, _ < ` < Q< r '�y1w05°° 'rrR1�e V.' r •r I <' Trcp!c t Sr 7 •FS �tiN Nt +ram NE a Cat E 4 N,'00 ST-'• �'• a i � l t f >� lla0 t W ..� �' o i .. r Ao a g Ct RENra '� Ii ^ ♦ N Al MY R Y' 3 L_ _ ? I J2ND ST S TFEIF si RT '� rIl11M 2 8 II00 NE 3100 ■ ,, „I 2-- ST <._� S TOB1N sr ST •" A '•'"f'G �a CTH :j $ + s VICTOR14 < Ko ,N s 17 L LLIaa 1=3I I u r ST 18 (RFNTON= "" Aw- ' # < WWI` FSTAUS ^Rica. 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" N S�4 u 11r r �C F ' I TX o �1.';SEi_._ ITfND sT : e SE11tra sib L-'.".SEA= 17 n IQ' ST G u�tsr 1 �' : IOBf10 __ �.� SE;li•D:f�-{'_i 17200 �� nir 17ft10 �IN N i < �F i 1 Nr ;• •I )t -i s s a asj , al a �'2 x i,�ar sl " 113n s 11JN ST k rn:r f PC L - SE I15_TH ^�I yIIST r�v sE SE I.�. �.•1 Y 394H ST n - >� 's F\ SE 176TH ST S7 •—y I< ~LSE 176Tp sr pEtt d< ' IIST ST S 1+ne n 4 0l �F•`• SI _ _. �� L7� .u,. _ _.< -> 1 FIGURE 1 yy,p. 11-10496-01 HIGH AVENUE SOUTH OUTFALL O AG R A DESIGN CRT RENTON, WASH NGTON ' Earth & Environmental DRAWN JMR 11335 N.E. 122nd Way, Suite 100 DATE JAN 1996 LOCATION MAP Kirkland, WA, U.S.A. 98034-6918 SCALE N.T.S. 1 AGRA EARTH k ENVIRONMENTAL, INC. DRAWING NO. 11 10496-01 LOCATION.DWG / 7OF / S ' LANDSCAPE BARK AND PLANTINGS LANDSCAPE TIMBERS 1 REFLECTOR \ SIGNS 12" CMP OUTFACE GRAVEL — -- UNDERGROUND HIGH DRAINAGE PIPE AVENUE SOUTH ' DRAINAGE --- CHANNEL JB—1 ASPHALT — DRIVEWAY SPRINKLER / HEAD BRICK 1 GRASS I r t 2 � N 1 m 525 HIGH LEGEND AVENUE SOUTH B'1 BORING NUMBER AND TOP APPROXIMATE LOCATION OF SLOPE 0 20 40 DRAWING BASED ON CITY OF RENTON, DEPARTMENT OF PUBLIC WORKS SCALE IN FEET PLAN WTR 27-2028. FIGURE 2 W.O. 11-10496-01 HIGH AVENUE IN O AG R A DESIGN CRT RENTON WASHGTON ' Earth &Environmental DRAWN JMR 11335 N.E. 122nd Way, Suite 100 DATE JAN 1996 SITE PLAN Kirkland, WA, U.S.A. 98034-6918 SCALE 1"=20' AGRA EARTH do ENVIRONMENTAL, INC. DRAWING NO. 11 10496 SITE.DWG ' CMP backfill — slope fill — Very loose to loose, 340 silty SAND with some gravel to gravelly CATCH BASIN 340 Qit — Recessional kame terrace 12" CMP deposits — Loose to medium B-1 dense SAND — gravelly SAND — --— ————— 320 Fill— z — —— 320 Very stiif to hard, Qit — — --' 34 — Qu —undifferentiated Till sandy SILT to silty SAND layers and interbedded Glacilfluvial SAND — 16 300 gravelly SAND Qu 26 32 _ —9 300 Quarry spalls 34 280 on surface Qu _ _ _ _ 280 Medium dense to dense, SAND — gravelly SAND Qu — Dense, silty SAND 260 - - - - - - - - - - - - - -? ' SANDSTONE 26O W LWLJ L_ ' Z 240 LEGEND 240 Z Renton Formation (Tr) O — — — — Q INTERFACE LINE > 220 — — _, 220 J — COAL W _ — — COAL aid SILTSTONE ® DEBRIS 200 — — — — COAL Debris Dam Debris Dam — — — — SILTST — ? 200 trees and soil — Quarry spalls and trees SANDSTONE B_1 BORING NUMBER AND accumulated sands, silts APPROXIMATE LOCATION 180 gravels from upslope II STANDARD PENETRATION TEST 180 ' 34 j� — BLOWS PER FOOT 160 — — — — — — — — 160 NOTE: THE STRATA ARE BASED UPON SILTSTONE INTERPOLATION OF OUR TEST BORING AND FIELD RECONNAISSANCE AND PUBLISHED 140 GEOLOGIC LITERATURE AND MAY 140 NOT REPRESENT ACTUAL — — — — — _? SUBSURFACE CONDITIONS. ' SANDSTONE — SILTSTONE — COAL SEAM 120 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1120 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40 -60 -70 -80 -100 DISTANCE IN FEET ALONG OF PROFILE FIGURE 3 W.O. 11-10496-01 HIGH AVENUE SOUTH OUTFALL *A® R A DESIGN CRT RENTON, WASHINGTON Earth &Environmental DRAWN JMR 11335 N.E. 122nd Way, Suite 100 DATE JAN 1996 GROUND SURFACE GEOLOGIC PROFILE Kirkland, WA, U.S.A. 98034-6918 SCALE 1"-30 AGRA EARTH do ENVIRONMENTAL, INC. DRAWING NO. 11 10496 X—S—A.DWG O o �O� TPA-5 ' o Y ' 0 20 40 `f-- SCALE IN FEET TP-3 ' c DRAINAGE„_ PATH 120 OUTLET STRUCTURE TP-2 / c \ ' TP--4 1 r3O I \1 ISO \ I �40 TPP-1 NEW 12" SHDPE PIPE / 1 i LEGEND / P TP-5 TEST PIT NUMBER AND O APPROXIMATE LOCATION OQ 1 FIGURE 4 W.O. 11-10496-01 HIGH AVENUE OUTFALL ' * AG R A DESIGN CRT _ RENTON, WASHINGTON LU Earth & Environmental DRAWN DMW 11335 NE 122nd Way, Suite 100 DATE MAY 1996 SITE & EXPLORATION PLAN ' Kirkland, Washington, U.S.A. 98034-6918 OUTLET STRUCTURE a: SCALE 1"=20' a Appendix A APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS 1 1-1 0496-01 ' *AGRA Earth & Environmental APPENDIX A 1 1-1 0496-01 SUBSURFACE EXPLORATION The field exploration program conducted for this study consisted of advancing one hollow-stem auger test boring and excavating five test pits. The exploration locations were obtained in the field by pacing from site features shown on a site map provided us. The approximate locations of our explorations are indicated on the Site and Exploration Plan, Figure 2. The locations of the explorations should be considered accurate only to the degree implied by the method used. ' Hollow-Stem Auger Boring The test boring was drilled by a local exploration drilling company under subcontract to our firm on 16 January 1996. The boring consisted of advancing a 4% inside diameter (ID) hollow-stem ' auger with a truck-mounted CME 85 drill rig. During the drilling process, samples were obtained at generally 2.5 to 5.0 foot depth intervals. The borings were continuously observed and logged by an engineering geologist from our firm. Disturbed samples were obtained by using the Standard Penetration Test procedures as ' described in ASTM:D 1586. This test and sampling method consist of driving a standard 2-inch outside diameter split barrel sampler a distance of 18 inches into the soil with a 140 pound hammer free-falling a distance of 30 inches. The number of blows for each 6-inch interval is ' recorded. The number of blows required to drive the sampler the final 12 inches is considered the Standard Penetration Resistance ("N") or blow count. The blow count is presented graphically on the boring logs in this appendix. If a total of 50 blow is recorded within one 6- inch interval, the blow count is recorded as 50 blows for the number of inches of penetration. The resistance, or "N" value, provides a measure of relative density or granular soils or the relative consistency of cohesive soils. ' The soil samples obtained from the split-barrel sampler were classified in the field and representative potions were placed in plastic containers. The samples were then transported ' to our laboratory for further visual classification and laboratory testing. Samples are generally saved for a period of 30 days unless special arrangements are made. The boring log presented in this appendix is based on the drilling action, inspection of the samples secured, laboratory results, and the field log. The various types of soils are indicated, as well as the depths where the soils or characteristics of the soils changed. It should be noted ' that these changes may have been gradational, and if the changes occurred between sample intervals, they were inferred. The groundwater conditions observed during the exploration program are indicated on the boring or test pit logs, where appropriate. The subsurface water conditions were evaluated by ' observing the free water on the sampling rods for the boring explorations and moisture conditions of the samples and side walls for the test pits. The groundwater level is indicated on the boring logs by a triangular symbol and the designation "ATD" (At Time of Drilling). The groundwater depth shown on the boring log is generally indicative of the open water level in ' 4AGRA Earth & Environmental the boring at the time the boring was advanced, but does not necessarily represent the true regional groundwater table. Test Pit Excavations Five test pits were excavated on 15 January 1996 with a track-mounted backhoe operated by a local excavation contractor. Each test pit was continuously logged and observed by one of our experienced engineering geologists. In-situ strength and quality attributes of materials encountered in the test pits were estimated by our field observer based on experience with similar soils and on the difficulty incurred during excavation. Disturbed, but representative, samples of the soils in the test pits were retrieved, classified in the field, and transported in plastic containers to our laboratory for further evaluation and classification. The test pit logs presented in this appendix are based on inspection of the soil samples and the field logs. ' L,AGRA Earth & Environmental PROJECT: High Avenue South Outfall w.o. 1 1- 10496-0 7 BORING NO. 8- 1 SOIL DESCRIPTION a3 PENETRATION RESISTANCE Page 1 W A v Location: See Site Plan A of 2 roxi ground surface elevation: feet ¢ 3 Standard Blows per foot Other PP mate� f lti 326 0 0 10 20 30 40 50 TESTING A Crushed Rock(Fill) N/E ---ry———————————�9 --y -- =------- -------................--------------------------......._....... Ve loose,moist,brown,silty,gravelly SAND with some organics(Fill) .............. ----------------------------- S-1 ------- ....... ..............................=....... ----------------------- ------- ' 5 Loose,moist,brown,fine to medium SAND with some coarse sand,trace gravel,silt and S-2 organics - - ---- ------ -------'....... a --------'------ -------?-------....... ... -- -- �-------------------------------- ----------- S-3 ..............1 •-•--- -- ......- •-- 10 ---------------------------- Very stiff to hard,moist,brown,sandy SILT with S-4 ..... ... ------------------------ trace to some gravel and interbedded oxidized orange,fine to medium SAND(1/4'- 1/2'zones) <----- ------- --................-....--- .............. s- -------;....... ' S-5 -- . 15 S-6 -- ---....>. i ——— .... ......... ............ . ............ ................. Very stiff,moist,brown/gray,sandy SILT with some gravel S-7 20 .............. ....... i .. -----................ ---- -------,.....------ ........ --------.... ------ S-8 Grades with some clay,trace gravel ........------- ------->-------........`........-----------� -- ... 25 - ......._................ Hard,moist to wet,brown/gray,sandy SILT with some gravel and interbedded oxidized orange, --=------- ------->- fine to medium SAND(1/4'- 1/2'zones) ------- ------- ---:...............;......... .....>....... .......,........ S-9 ------ ----------------------s..-------- - - -- ........ (continued) 30 0 20 40 so 80 ioa MOISTURE CONTENT LEGEND C e Plastic limit Natural Liquid limit ° 2.00-inch OD split-spoon sample ® Grain size analysis -S' , AG R A� Earth & Environmental ca N/E No groundwater encountered w 11335 NE 122nd Way,Suite 100 Kirkland,Washington 98034-6918 a Drilling method: HSA Hammer type: Automatic Date drilled: 16 January 7996 Logged by: CRT PROJECT: High Avenue South Outfoll w.o. 11-10496-01 BORING NO. 8-1 SOIL DESCRIPTION N M 2 PENETRATION RESISTANCE page 2 W W A ° Location: See Site Plan a of 2 A v Approximate ground surface elevation: 326 feet N CA3 0 Standard B10 2ocws per 3o t Other 40 so TESTIlJG 30 Some as above N/E ——————————— ........>................-------•......................-................-....... Dense,moist,brown,fine to medium SAND with ' trace coarse sand,gravel and silt .. -"""" ................ ---""" ................!.......... ...:... ......... !....... ------- ....... TS-10 - ......... =-•--... ...... .. ... 35 —— — ............................. ....... ....... ....... Grades with coarser SAND,some gravel to gravelly •.... ....... ......•----•-•-••------------ ------ ----........... i ."..............r.......................... .. ....... ............... S-17 ! 40 Boring terminated at approximately 39 feet i ! -. -. .. ..........--•.....:.......... ... ....... .. -•! .....•........ .......i.--- --------1............... ....... ....... ....... ................ ......._...................................... ........ .. I : 45 >....... ................... ....... ...... --------I.................•••••• ------- ---------------- -....... 50 - ------ ------ -------'.......................... -- ... .. ------- ----.". ...............i•••...............-•--- ............... ------ ------- ---------•-----..... ... • •• - .............. ••••••._.....----------..............._....... .......,-------- ' 55 ....... ......._.......--------............... ....... --------------- 60 0 20 40 so 80 100 MOISTURE CONTENT LEGEND ' a Plastic limit Natural Liquid limit 2.00-inch OD split-spoon sample ® Grain size analysis W , AG R A g Earth & Environmental cc N/E No groundwater encountered w 11335 NE 122nd Way,Suite 100 Kirkland,Washington 98034-6918 ' a Drilling method: HSA Hammer type: Automatic Date drilled: 76 January 7996 Logged by: CRT TEST PIT LOGS 11-10496-01 Depth (feet) Material Description Test Pit TP-1 Location: See Site Plan Approximate ground surface elevation: Unknown ' 0.0 - 3.0 Forest duff atop very loose, moist to wet, dark brown, silty SAND to sandy SILT with some organics, gravel, coal, brick ' fragments and substantial roots (Fill and/or Colluvium). 3.0 - 10.0 Loose to medium dense, wet, brown/gray, silty SAND with some gravel, coal and wood fragments (Fill and/or Colluvium). 10.0 - 13.0 Medium dense, moist to wet, tan-brown, silty SAND with some gravel (Weathered Sandstone). ' Test pit terminated at approximately 13.0 feet Severe caving at 0 to 10.0 feet i Slow seepage at 3.0 feet Moderate seepage at 10.0 feet 1 Test Pit TP-2 ' Location: See Site Plan Approximate ground surface elevation: Unknown 0.0 - 2.5 Forest duff atop soft, moist to wet, black, sandy SILT with some organics, gravel and substantial roots (Fill and/or Colluvium). 2.5 - 9.0 Loose to medium dense, wet, brown, silty SAND with some gravel, coal and wood fragments (Fill and/or Colluvium). 9.0 - 11.0 Medium dense, wet, blue-gray, silty SAND with some gravel. ' Test pit terminated at approximately 11.0 feet Severe caving from 0 to 9.0 feet Moderate seepage at 3.5 feet ' Rapid seepage at 9.0 feet 1 1 1-1 0496-01 Test Pit Log, Page 2 Depth feet Material Description Test Pit TP-3 Location: See Site Plan ' Approximate ground surface elevation: Unknown 0.0 - 1 .5 Forest duff atop very loose, moist to wet, brown-gray-black, ' silty SAND with some organics, gravel and substantial roots (Fill and/or Colluvium). 1 .5 - 10.0 Loose, wet, brown-gray-black, gravelly, silty SAND with some wood, coal, and moderate roots to 3.0 feet (Fill and/or Colluvium). 10.0 - 12.0 Medium dense, wet, gray, silty SAND with some gravel and interbedded sandy SILT. Test pit terminated at approximately 12.0 feet iModerate to Severe caving 0 to 10 feet Rapid seepage at 5.0 feet 1 Test Pit TP-4 iLocation: See Site Plan Approximate ground surface elevation: Unknown 0.0 - 3.0 Forest duff atop very soft, wet, brown, sandy SILT with some clay, wood debris including timbers, trace gravel, and moderate ' roots (Fill and/or Colluvium). 3.0 - 8.0 Soft, wet, brown-gray, sandy SILT with some clay, brick, and coal fragments and wood debris including timbers (Fill and/or ' Colluvium). Test pit terminated at approximately 8.0 feet ' Severe caving 0 to 8.0 feet, requires stoppage due to caving conditions Moderate surficial seepage Rapid seepage at 1.5 feet i t1 1-1 0496-01 Test Pit Log, Page 3 ' Depth (feet) Material Description Test Pit TP-5 Location: See Site Plan Approximate ground surface elevation: Unknown 0.0 - 1 .5 Forest duff atop very loose, wet, black, silty SAND to sandy SILT with some organics, trace gravel and substantial roots (Fill and/or Colluvium). 1.5 - 3.0 Loose, wet, brown-gray, silty, gravelly SAND with some organics and substantial roots (Fill and/or Colluvium). 3.0 - 8.0 Loose, saturated, brown-gray, silty SAND with some gravel, logs, wood debris and coal (Fill and/or Colluvium). 8.0 - 10.0 Medium dense, wet, blue-gray, silty SAND with some gravel. Test pit terminated at approximately 10.0 feet Severe caving 0 to 8.0 feet Rapid seepage at 3.0 feet Date excavated: 15 January 1996 Logged by: CRT r Appendix B 1 1 i 1 1 APPENDIX B LABORATORY PROCEDURES AND RESULTS 11-10496-01 1 i AG RA Earth & Environmental IAPPENDIX B 11-10496-01 LABORATORY TESTING PROCEDURES A series of laboratory tests were performed during the course of this study to evaluate the index and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests performed are given below. Visual Classification Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in watertight containers and transported to our laboratory where the filed classifications were ' verified or modified as required. Visual classification was generally done in accordance with the Unified Soil Classification system. Visual soil classification includes evaluation of color, relative moisture content, soil type based on grain size, and accessory soil types included in the sample. Soil classifications are presented on the boring and test pit logs in Appendix A. Moisture Content Determinations ' Moisture content determinations were performed on representative samples obtained from the explorations in order to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM:D-2216. The ' results of the tests are listed in this Appendix and presented on the boring log in Appendix A. 1 Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. A grain size analysis was performed on representative samples in general accordance ' with ASTM:D-422. The results of the grain size determination for the samples were used in classification of the soils, and is presented in this Appendix. ' L,AGRA Earth & Environmental MOISTURE CONTENT l Job Name: High Ave. South Outfall Job Number: 1 1-1 0496-01 Date: 1-17-96 Exploration: B-1 B-1 B-1 B-1 B-1 B-1 TP-1 TP-2 TP-2 TP-3 Sample Number: S-1 S-2 S-6 S-8 S-9 S-11 Depth: 2.5' 5.0' 15.9 22.5' 27.5' 37.5' 3.0-10.0' 0.&2.5' 2.5-9.9 0.0-1.5' Wet weight: Dia. of sample: Length of Sample: Volume (cf): Wet Density: Dry Density: Wet sample +tare: 347 475 538 424 607 651 714 492 586 692 Dry sample+tare: 335 458 500 375 528 637 645 419 532 619 Water: 12 18 38 49 79 14 69 73 54 73 Tare: 161 162 162 169 162 161 167 155 165 167 Moisture Content: 7% 6% 11% 24% 22% 3% 14% 27% 15% 16% Exploration: TP-3 TP-4 TP-4 Sample Number: ' Depth: 10.0-12.0' 0.0-3.0' 3.0-8.0' Wet weight: Dia. of sample: Length of Sample: ' Volume (cf): Wet Density: Dry Density: Wet sample +tare: 725 664 646 Dry sample+tare: 637 541 523 Water: 88 123 123 0 0 0 0 0 0 0 ' Tare: 167 163 155 Moisture Content: 19% 33% 33% ' Exploration: Sample Number: Depth: Wet weight: 1 Dia. of sample: Length of Sample: Volume (cf): Wet Density: Dry Density: Wet sample +tare: Dry sample+tare: Water: 0 0 0 0 0 0 0 0 0 0 Tare: Moisture Content: GRAIN SIZE DISTRIBUTION ' SIZE OF OPENING IN INCHES U.S. STANDARD SIEVE SIZE HYDROMETER 36' 12' 6' 3" 1 1/2" 3/4" 3/8' 4 10 20 40 60 100 200 100 90 80— t 2 70 \ 60 \ m \ W 50 Z LL �c W U a_ 30 a 20 ' 10 1 0 1000.00 100.00 10.00 1.00 0.10 0.01 0.00 GRAIN SIZE IN MILLIMETERS Coarse Fine Coarse Medium Fine Sift Clay WD FINE GRNNED Exploration Sample Depth Moisture Fines Soil Description f i F♦ B-1 S-3 7.5' 8% 2% SAND,trace silt • f-�-�-• B-1 S4 10.9 15% 48% Sandy SILT,trace gravel - TP-3 1.5-10.0' 27% 32% Gravelly Silty SAND Project: High Ave South OutFall *AGRA Work Order: 11-10496-01 Earth & Environmental Date: 1-17-96 11335 NE 122nd Way Suite 100 ' Kirkland, Washington 98034-6918