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HomeMy WebLinkAboutGeotech Report E RA 3 Geotechnical Engineering Report 701 Sunset Blvd NE Renton, Washington P/Ns 311990001, 3119900010, 3119900005 Submitted to: Totenham, LLC Attn: Joe Notarangelo 50 116th Ave SE, Suite 111 Bellevue, Washington 98004 Submitted by: E3RA, Inc. PO Box 44840 Tacoma, Washington 98448 (253) 537-9400 April 16, 2015 Project No. T15034 i TABLE OF CONTENTS Page No. 1.0 SITE AND PROJECT DESCRIPTION .................................................................................... 1 2.0 EXPLORATORY METHODS ................................................................................................... 2 2.1 Test Pit Procedures ..................................................................................................... 2 3.0 SITE CONDITIONS ................................................................................................................. 3 3.1 Surface Conditions....................................................................................................... 3 3.2 Soil Conditions ............................................................................................................. 3 3.3 Groundwater Conditions .............................................................................................. 3 3.4 Seismic Conditions ...................................................................................................... 4 3.5 Liquefaction Potential .................................................................................................. 4 4.0 CONCLUSIONS AND RECOMMENDATIONS ....................................................................... 4 4.1 Site Preparation ........................................................................................................... 5 4.2 Spread Footings ........................................................................................................... 7 4.3 Slab-On-Grade Floors.................................................................................................. 8 4.4 Asphalt Pavement ........................................................................................................ 8 4.5 Structural Fill ................................................................................................................ 9 5.0 RECOMMENDED ADDITIONAL SERVICES ........................................................................ 10 6.0 CLOSURE .............................................................................................................................. 11 List of Tables Table 1. Approximate Locations and Depths of Explorations ...................................................................... 2 List of Figures Figure 1. Topographic and Location Map Figure 2. Site and Exploration Plan APPENDIX A Soil Classification Chart and Key to Test Data ........................................................................................... A-1 Logs of Test Pits TP-1 through TP-3................................................................................................ A-2…A-4 PO Box 44840 Tacoma, WA 98448 253-537-9400 253-537-9401 Fax E3RA April 16, 2015 T15034 Totenham, LLC 50 116th Ave SE, Suite 111 Bellevue, WA 98004 Attention: Joe Notarangelo Subject: Geotechnical Engineering Report 701 Sunset Blvd NE P/Ns 3119900011, 3119900010, 3119900005 Renton, Washington Dear Mr. Notarangelo: E3RA, Inc. (E3RA) is pleased to submit this revised report describing the results of our geotechnical engineering evaluation for the improvements planned at 701 Sunset Blvd NE in Renton, Washington. This report has been prepared for the exclusive use of the Totenham, LLC and their consultants, for specific application to this project, in accordance with generally accepted geotechnical engineering practice. 1.0 SITE AND PROJECT DESCRIPTION The project site consists of three separate, but adjacent tax parcels on the west side of Sunset Blvd NE, located directly northwest of its intersection with NE 7th St in Renton, Washington, as shown on the enclosed Topographic and Location Map (Figure 1). The subject property contains a frontage on Sunset Blvd NE of approximately 200 feet, and extends west of the roadway ± 125 to 200 feet; encompassing just under one acre. Currently, the property is undeveloped, with the only distinguishing site feature being a “U” shaped gravel driveway which enters/exits Sunset Blvd NE along the east side of the site. Generally, the easternmost two-thirds of the property is relatively level, containing a slight slope from east to west, no steeper than 15 percent. The western third of the site consists of a moderate to steep slope which descends to the west at grades of 50 to 60 percent and represents an elevation change of 15 to 20 feet. Directly west of the subject property is long, thin parcel owned by Puget Sound Energy, which acts as a pathway for transmission towers which service the area. One such transmission tower is in close proximity to the project area. Areas west of this parcel are steeply sloped, and descend down to I-405. The western boundary of the site is approximately 200 feet east of I-405. Improvement plans involve the clearing/stripping of the site and developing 10 to 12 townhouses within its confines. Preliminary discussions have the townhouses being three-story, wood-framed structures. Garages will either be attached or detached, with no preliminary layouts available thus far. Paved driving and parking surfaces will also be incorporated into the proposed development. April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 2 2.0 EXPLORATORY METHODS We previously explored surface and subsurface conditions at the project site on January 21, 2015. Our exploration and evaluation program comprised the following elements: • Surface reconnaissance of the site; • Three test pits (designated TP-1 through TP-3), advanced on January 21, 2015; and • A review of published geologic and seismologic maps and literature. Table 1 summarizes the approximate functional locations and termination depths of our subsurface explorations, and Figure 2 depicts their approximate relative locations. The following sections describe the procedures used for excavation of test pits. TABLE 1 APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS Exploration Functional Location Termination Depth (feet) TP-1 TP-2 TP-3 Eastern third of the site, north end of “U” shaped gravel driveway Eastern third of the site, south end of “U” shaped gravel driveway Centrally within the site, west of the “U” shaped gravel driveway 7½ 7½ 7½ The specific number and locations of our explorations were selected in relation to the existing site features, under the constraints of surface access, underground utility conflicts, and budget considerations. It should be realized that the explorations performed and utilized for this evaluation reveal subsurface conditions only at discrete locations across the project site and that actual conditions in other areas could vary. Furthermore, the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have begun. If significant variations are observed at that time, we may need to modify our conclusions and recommendations contained in this report to reflect the actual site conditions. 2.1 Test Pit Procedures Our exploratory test pits were excavated with a rubber-tracked mini-excavator operated by an excavation contractor under subcontract to E3RA. A geotechnical engineer from our firm observed the test pit excavations, collected soil samples, and logged the subsurface conditions. The enclosed test pit logs indicate the vertical sequence of soils and materials encountered in each test pit, based on our field classifications. Where a soil contact was observed to be gradational or undulating, our logs indicate the average contact depth. We estimated the relative density and consistency of the in-situ soils by means of the excavation characteristics and the stability of the test pit sidewalls. Our logs also indicate the approximate depths of any sidewall caving or groundwater seepage observed in the test pits. The soils were classified visually in general accordance with the system described in Figure A-1, which includes a key to the exploration logs. Summary logs of the explorations are included as Figures A-2 through A-4. April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 3 3.0 SITE CONDITIONS The following sections present our observations, measurements, findings, and interpretations regarding, surface, soil, groundwater, and infiltration conditions. 3.1 Surface Conditions As previously described, the project site consists of three separate but adjacent tax parcels on the west side of Sunset Blvd NE, located directly northwest of its intersection with NE 7th St, in Renton, Washington. It is located on the outskirts of a larger residential development further to the east, and is positioned on the top of a small ridgeline which runs north/south, forming the eastern boundary of I-405. The eastern two-thirds of the site is relatively level, containing a slight slope (less than 15 percent) from east to west. This portion of the site has limited vegetation, containing only a sparse grass cover and limited gravel surfacing along the “U” shaped driveway. The western third of the site consists of a moderate to steep slope which descends to the west at grades of 50 to 60 percent and represents an elevation change of 15 to 20 feet. The slope face itself is densely vegetated with thin conifers, blackberry bushes, and other brush, and does not display any irregularities indicating slope failure, such as ancient or recent landslide scarps, hummocks, slide blocks, or jack-strawed trees. The adjacent property to the west is owned by Puget Sound Energy, and acts as a pathway for transmission towers servicing the area. A narrow driveway to this property is located directly south of the project site. The western boundary of the PSE property is marked by a chainlink fence, with areas west of this mark being steeply sloped and directly descend down to I-405. No hydrologic features were observed on site, such as seeps, springs, ponds and streams. 3.2 Soil Conditions Our subsurface explorations revealed relatively consistent subgrade conditions across the site. The entirety of the site contains a surface mantle of sod, topsoil, or gravel surfacing, typically no more than 6 inches thick. Underlying this material, a fill zone spans much of the site, typically extending to 4½ feet below existing grade. The uppermost 3 feet of the fill material is comprised of silty sand in a medium dense in-situ condition. From 3½ to 4½ feet below existing grade, logs, woody debris and general refuse were incorporated into the fill material. Native soils on site consist of glacial till deposited during the most recent glaciation of the area; the Vashon Stade of the Fraser Glaciation. Glacial till deposits observed in our subsurface explorations were all moderately weathered and comprised of gravelly, silty sand in a medium dense in-situ condition. Unweathered deposited are likely encountered with depth. In the Geologic Map of the Renton Quadrangle, King County, Washington, as prepared by the Department of the Interior United States Geological Survey (USGS) (1965), the project site is mapped as containing Qgt, or Vashon Glacial Till. These deposits are described as being a generally compact, coherent, unsorted mixture of sand, silt, clay and gravel. Our subsurface explorations generally correspond with the mapping performed by the USGS. The enclosed exploration logs (Appendix A) provide a detailed description of the soil strata encountered in our subsurface explorations. 3.3 Groundwater Conditions At the time of our reconnaissance and subsurface explorations (January 21, 2015), we did not encounter groundwater seepage in any of our subsurface explorations which extended to a maximum depth of 7½ feet below existing grade. Given the fact that our subsurface explorations were performed in what is generally April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 4 considered the wet season (December through April), we do not anticipate that groundwater levels will rise higher than that which we observed, and we do not anticipate that groundwater will adversely impact the proposed improvements. 3.4 Seismic Conditions Based on our analysis of subsurface exploration logs and our review of published geologic maps, we interpret the onsite soil conditions to generally correspond with site class D, as defined by Table 20.3-1 in ASCE 7, per the 2012 International Building Code (IBC). Using 2012 IBC information on the USGS Design Summary Report website, Risk Category I/II/III seismic parameters for the site are as follows: Ss = 1.436 g SMS = 1.436 g SDS = 0.957 g S1 = 0.539 g SM1 = 0.809 g SD1 = 0.539 g Using the 2012 IBC information, MCER Response Spectrum Graph on the USGS Design Summary Report website, Risk Category I/II/III, Sa at a period of 0.2 seconds is 1.44 g and Sa at a period of 1.0 seconds is 0.54g. The Design Response Spectrum Graph from the same website, using the same IBC information and Risk Category, Sa at a period of 0.2 seconds is 0.96 g and Sa at a period of 1.0 seconds is 0.54g. 3.5 Liquefaction Potential Liquefaction is a sudden increase in pore water pressure and a sudden loss of soil shear strength caused by shear strains, as could result from an earthquake. Research has shown that saturated, loose, fine to medium sands with a fines (silt and clay) content less than about 20 percent are most susceptible to liquefaction. Our subsurface explorations did not encounter any loose sand layers or lenses. 4.0 CONCLUSIONS AND RECOMMENDATIONS Improvement plans involve the clearing/stripping of the site and developing 10 to 12 townhouses within its confines. Preliminary discussions have the townhouses being three-story, wood-framed structures. Garages will either be attached or detached, with no preliminary layouts yet available. Paved driving and parking surfaces will also be incorporated into the proposed development. We offer these recommendations: • Feasibility: Based on our field explorations, research, and evaluations, the proposed structure and pavements appear feasible from a geotechnical standpoint. • Foundation Options: Given the fact that a zone of organic-laden fill material underlies the site and could result in post-construction settlement if not removed, we recommend the over- excavation of the building footprint down to native soils; a depth of approximately 4½ feet. Foundation elements should be constructed on undisturbed native soils, or on structural fill bearing pads that extend down to native soils. The thickness of structural fill bearing pads, if used, is at the discretion of the developer. Recommendations for Spread Footings are provided in Section 4.2. • Floor Options: Floor sections should bear on medium dense or denser native soils or on properly compacted structural fill that extends down to medium dense or denser native soil. We recommend over-excavation of slab-on-grade floor subgrades to a minimum depth of April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 5 4½ feet. Slab-on-grade floors should either be constructed on undisturbed native soils or on properly compacted structural fill as a floor subbase. If floor construction occurs during wet conditions, it is likely that a geotextile fabric, placed between the structural fill floor subbase and native soils, will be necessary. Recommendations for slab-on-grade floors are included in Section 4.3. Fill underlying floor slabs should be compacted to 95 percent (ASTM:D-1557). • Pavement Sections: After removal of any organics underlying pavements, we recommend a conventional pavement section comprised of an asphalt concrete pavement over a crushed rock base course over a properly prepared (compacted) subgrade or a granular subbase. All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be overexcavated to a depth of 12 inches and replaced with a suitable structural fill material. The following sections of this report present our specific geotechnical conclusions and recommendations concerning site preparation, spread footings, slab-on-grade floors, asphalt pavement, and structural fill. The Washington State Department of Transportation (WSDOT) Standard Specifications and Standard Plans cited herein refer to WSDOT publications M41-10, Standard Specifications for Road, Bridge, and Municipal Construction, and M21-01, Standard Plans for Road, Bridge, and Municipal Construction, respectively. 4.1 Site Preparation Preparation of the project site should involve erosion control, temporary drainage, clearing, stripping, excavations, cutting, subgrade compaction, and filling. Erosion Control: Before new construction begins, an appropriate erosion control system should be installed. This system should collect and filter all surface water runoff through silt fencing. We anticipate a system of berms and drainage ditches around construction areas will provide an adequate collection system. Silt fencing fabric should meet the requirements of WSDOT Standard Specification 9-33.2 Table 3. In addition, silt fencing should embed a minimum of 6 inches below existing grade. An erosion control system requires occasional observation and maintenance. Specifically, holes in the filter and areas where the filter has shifted above ground surface should be replaced or repaired as soon as they are identified. Temporary Drainage: We recommend intercepting and diverting any potential sources of surface or near-surface water within the construction zones before stripping begins. Because the selection of an appropriate drainage system will depend on the water quantity, season, weather conditions, construction sequence, and contractor's methods, final decisions regarding drainage systems are best made in the field at the time of construction. Based on our current understanding of the construction plans, surface and subsurface conditions, we anticipate that curbs, berms, or ditches placed around the work areas will adequately intercept surface water runoff. Clearing and Stripping: After surface and near-surface water sources have been controlled, sod, topsoil, and root-rich soil should be stripped from the site. Our explorations and field observations indicate that the topsoil horizon is typically 6 inches or less in overall thickness. An organic ridden fill zone was encountered from 3½ to 4½ feet below existing grade, which will also need to be over-excavated within the proposed building footprint. Stripping is best performed during a period of dry weather. April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 6 Site Excavations: Based on our explorations, we expect that excavations will encounter loose to medium dense silty fill soils and weathered glacial till which can be easily excavated using standard excavation equipment. Dewatering: Groundwater was not observed in any of our test pit explorations which extended to a maximum depth of 7½ below existing grade. Given the fact that our test pit explorations were performed in what is generally considered the rainy season, we do not anticipate that groundwater levels will rise higher than that which we observed, nor do we anticipate that groundwater will adversely affect the proposed development. If groundwater is encountered, we anticipate that an internal system of ditches, sumpholes, and pumps will be adequate to temporarily dewater excavations. Temporary Cut Slopes: All temporary soil slopes associated with site cutting or excavations should be adequately inclined to prevent sloughing and collapse. Temporary cut slopes in site soils should be no steeper than 1½H:1V, and should conform to Washington Industrial Safety and Health Act (WISHA) regulations. Subgrade Compaction: Exposed subgrades for the foundations of the planned additions should be compacted to a firm, unyielding state before new concrete or fill soils are placed. Any localized zones of looser granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast, any organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. Site Filling: Our conclusions regarding the reuse of onsite soils and our comments regarding wet-weather filling are presented subsequently. Regardless of soil type, all fill should be placed and compacted according to our recommendations presented in the Structural Fill section of this report. Specifically, building pad fill soil should be compacted to a uniform density of at least 95 percent (based on ASTM:D-1557). Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as structural fill: • Surficial Organic Soil and Organic-Rich Fill Soils: Where encountered, surficial organic soils, like duff, topsoil, root-rich soil, and organic-rich fill soils are not suitable for use as structural fill under any circumstances, due to high organic content. Consequently, this material can be used only for non-structural purposes, such as in landscaping areas. • Silty Sand Fill Soils: Much of the site is overlain by 4 feet of fill material. This material contains a high relative fines (percent silt/clay) content and should be considered extremely moisture sensitive. Reuse of this soil type should be limited to summer months and moisture conditioning should be anticipated. • Glacial Till: This material type underlies much of the project site and is encountered with depth. These soils are moisture sensitive and will be difficult to reuse during wet weather conditions. Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to reduce long-term raveling, sloughing, and erosion. We generally recommend that no permanent slopes be steeper than 2H:1V. For all soil types, the use of flatter slopes (such as 2½H:1V) would further reduce long-term erosion and facilitate revegetation. April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 7 Slope Protection: We recommend that a permanent berm, swale, or curb be constructed along the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover should be established as soon as feasible, to further protect the slopes from runoff water erosion. Alternatively, permanent slopes could be armored with quarry spalls or a geosynthetic erosion mat. 4.2 Spread Footings In our opinion, conventional spread footings will provide adequate support for the new additions if the subgrades are properly prepared. Footing Depths and Widths: For frost and erosion protection, the bases of all exterior footings should bear at least 18 inches below adjacent outside grades, whereas the bases of interior footings need bear only 12 inches below the surrounding slab surface level. To reduce post-construction settlements, continuous (wall) and isolated (column) footings should be at least 18 and 24 inches wide, respectively. Bearing Subgrades: Given the fact that a zone of organic-laden fill material underlies the site and could result in post-construction settlement if not removed, we recommend the over-excavation of the building footprint down to native soils; a depth of approximately 4½ feet. Foundation elements should be constructed on undisturbed native soils, or on structural fill bearing pads that extend down native soils and compacted to a density of at least 95 percent (based on ASTM:D-1557). The thickness of structural fill bearing pads, if used, is at the discretion of the developer. If foundation construction occurs during wet conditions, it is possible that a geotextile fabric, placed between the bearing pad and native soils, will be necessary. In general, before footing concrete is placed, any localized zones of loose soils exposed across the footing subgrades should be compacted to a firm, unyielding condition, and any localized zones of soft, organic, or debris-laden soils should be overexcavated and replaced with suitable structural fill. Lateral Overexcavations: Because foundation stresses are transferred outward as well as downward into the bearing soils, all structural fill placed under footings, should extend horizontally outward from the edge of each footing. This horizontal distance should be equal to the depth of placed fill. Therefore, placed fill that extends 24 inches below the footing base should also extend 24 inches outward from the footing edges. Subgrade Observation: All footing subgrades should consist of firm, unyielding, native soils, or structural fill materials that have been compacted to a density of at least 95 percent (based on ASTM:D-1557). Footings should never be cast atop loose, soft, or frozen soil, slough, debris, existing uncontrolled fill, or surfaces covered by standing water. Bearing Pressures: In our opinion, for static loading, footings that bear on a properly prepared subgrade, or structural fill bearing pads can be designed for a preliminary allowable soil bearing pressure of 2,000 psf. A one-third increase in allowable soil bearing capacity may be used for short-term loads created by seismic or wind related activities. Footing Settlements: Assuming that structural fill soils are compacted to a medium dense or denser state, we estimate that total post-construction settlements of properly designed footings bearing on properly prepared subgrades will not exceed 1 inch. Differential settlements for comparably loaded elements may approach one-half of the actual total settlement over horizontal distances of approximately 50 feet. April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 8 Footing Backfill: To provide erosion protection and lateral load resistance, we recommend that all footing excavations be backfilled on both sides of the footings and stemwalls after the concrete has cured. Either imported structural fill or non-organic onsite soils can be used for this purpose, contingent on suitable moisture content at the time of placement. Regardless of soil type, all footing backfill soil should be compacted to a density of at least 90 percent (based on ASTM:D-1557). Lateral Resistance: Footings that have been properly backfilled as recommended above will resist lateral movements by means of passive earth pressure and base friction. We recommend using an allowable passive earth pressure of 250 psf for and an allowable base friction coefficient of 0.35 for site soils. 4.3 Slab-On-Grade Floors In our opinion, soil-supported slab-on-grade floors can be used if the subgrades are properly prepared. We offer the following comments and recommendations concerning slab-on-grade floors. Floor Subbase: We recommend over-excavation of slab-on-grade floor subgrades to a minimum depth of 4 ½ feet. Slab-on-grade floors should either be constructed on undisturbed native soils or on properly compacted structural fill as a floor subbase. If floor construction occurs during wet conditions, it is likely that a geotextile fabric, placed between the structural fill floor subbase and native soils, will be necessary. All subbase fill should be compacted to a density of at least 95 percent (based on ASTM:D-1557). Capillary Break and Vapor Barrier: To retard the upward wicking of moisture beneath the floor slab, we recommend that a capillary break be placed over the 12 inch subbase. Ideally, this capillary break would consist of a 4-inch-thick layer of pea gravel or other clean, uniform, well-rounded gravel, such as “Gravel Backfill for Drains” per WSDOT Standard Specification 9-03.12(4), but clean angular gravel can be used if it adequately prevents capillary wicking. In addition, a layer of plastic sheeting (such as Crosstuff, Visqueen, or Moistop) should be placed over the capillary break to serve as a vapor barrier. During subsequent casting of the concrete slab, the contractor should exercise care to avoid puncturing this vapor barrier. 4.4 Asphalt Pavement Since asphalt pavements will be used for the new driveway and parking areas, we offer the following comments and recommendations for pavement design and construction. Subgrade Preparation: After removal of any surficial sod, topsoil, or organic-rich fill, all soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be over excavated to a maximum depth of 12 inches and replaced with a suitable structural fill material. All structural fill should be compacted according to our recommendations given in the Structural Fill section. Specifically, the upper 2 feet of soils underlying pavement section should be compacted to at least 95 percent (based on ASTM D-1557), and all soils below 2 feet should be compacted to at least 90 percent. Pavement Materials: For the base course, we recommend using imported crushed rock, such as "Crushed Surfacing Top Course” per WSDOT Standard Specification 9-03.9(3). If a subbase course is needed, we recommend using imported, clean, well-graded sand and gravel such as “Ballast” or “Gravel Borrow” per WSDOT Standard Specifications 9-03.9(1) and 9-03.14, respectively. April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 9 Conventional Asphalt Sections: A conventional pavement section typically comprises an asphalt concrete pavement over a crushed rock base course. We recommend using the following conventional pavement sections: Minimum Thickness Pavement Course Parking Areas Driveways Asphalt Concrete Pavement 2 inches 3 inches Crushed Rock Base 4 inches 6 inches Granular Fill Subbase (if needed) 6 inches 8 inches Compaction and Observation: All subbase and base course material should be compacted to at least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557), and all asphalt concrete should be compacted to at least 92 percent of the Rice value (ASTM D-2041). We recommend that an E3RA representative be retained to observe the compaction of each course before any overlying layer is placed. For the subbase and pavement course, compaction is best observed by means of frequent density testing. For the base course, methodology observations and hand-probing are more appropriate than density testing. Pavement Life and Maintenance: No asphalt pavement is maintenance-free. The above described pavement sections present our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. Furthermore, a 20-year pavement life typically assumes that an overlay will be placed after about 10 years. Thicker asphalt and/or thicker base and subbase courses would offer better long-term performance, but would cost more initially; thinner courses would be more susceptible to “alligator” cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. 4.5 Structural Fill The term "structural fill" refers to any material placed under foundations, retaining walls, slab-on-grade floors, sidewalks, pavements, and other structures. Our comments, conclusions, and recommendations concerning structural fill are presented in the following paragraphs. Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock, crushed rock, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit-run"), and miscellaneous mixtures of silt, sand, and gravel. Recycled asphalt, concrete, and glass, which are derived from pulverizing the parent materials, are also potentially useful as structural fill in certain applications. Soils used for structural fill should not contain any organic matter or debris, nor any individual particles greater than about 6 inches in diameter. Fill Placement: Clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a mechanical compactor. Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we recommend that structural fill used for various onsite applications be compacted to the following minimum densities: April 16, 2015 E3RA, Inc. T15034 / Totenham, LLC – 701 Sunset Blvd NE, Renton Geotechnical Engineering Report 10 Fill Application Minimum Compaction Footing subgrade and bearing pad Foundation backfill Slab-on-grade floor subgrade and subbase Asphalt pavement base Asphalt pavement subgrade (upper 2 feet) Asphalt pavement subgrade (below 2 feet) 95 percent 90 percent 95 percent 95 percent 95 percent 90 percent Subgrade Observation and Compaction Testing: Regardless of material or location, all structural fill should be placed over firm, unyielding subgrades prepared in accordance with the Site Preparation section of this report. The condition of all subgrades should be observed by geotechnical personnel before filling or construction begins. Also, fill soil compaction should be verified by means of in-place density tests performed during fill placement so that adequacy of soil compaction efforts may be evaluated as earthwork progresses. Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on their grain-size distribution and moisture content when they are placed. As the "fines" content (that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than 2 percentage points above or below optimum. For fill placement during wet-weather site work, we recommend using "clean" fill, which refers to soils that have a fines content of 5 percent or less (by weight) based on the soil fraction passing the U.S. No. 4 Sieve. 5.0 RECOMMENDED ADDITIONAL SERVICES Because the future performance and integrity of the structural elements will depend largely on proper site preparation, drainage, fill placement, and construction procedures, monitoring and testing by experienced geotechnical personnel should be considered an integral part of the construction process. Consequently, we recommend that E3RA be retained to provide the following post-report services: • Review all construction plans and specifications to verify that our design criteria presented in this report have been properly integrated into the design; • Prepare a letter summarizing all review comments (if required); • Check all completed subgrades for footings and slab-on-grade floors before concrete is poured, in order to verify their bearing capacity; • Prepare a post-construction letter summarizing all field observations, inspections, and test results (if required); and 701 Sunset Blvd NE Renton, Washington Topographic and Location Map FIGURE 1 T15034 APPROXIMATE SITE LOCATION E3RA, Inc. P.O. Box 44840 Tacoma, WA 98448 APPENDIX A SOIL CLASSIFICATION CHART AND KEY TO TEST DATA LOG OF TEST PITS CLAYEY GRAVELS, POORLY GRADED GRAVEL-SAND-CLAYMIXTURES SILTS AND CLAYSCOARSE GRAINED SOILSMore than Half > #200 sieveLIQUID LIMIT LESS THAN 50 LIQUID LIMIT GREATER THAN 50 CLEAN GRAVELS WITH LITTLE OR NO FINES GRAVELS WITH OVER 15% FINES CLEAN SANDS WITH LITTLE OR NO FINESMORE THAN HALF COARSE FRACTION IS SMALLER THAN NO. 4 SIEVE MORE THAN HALF COARSE FRACTION IS LARGER THAN NO. 4 SIEVE INORGANIC SILTS, MICACEOUS OR DIATOMACIOUS FINESANDY OR SILTY SOILS, ELASTIC SILTS ORGANIC CLAYS AND ORGANIC SILTY CLAYS OF LOWPLASTICITY OH INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR,SILTY OR CLAYEY FINE SANDS, OR CLAYEY SILTS WITHSLIGHT PLASTICITY CH SILTY GRAVELS, POORLY GRADED GRAVEL-SAND-SILT MIXTURES SANDS SILTS AND CLAYS Figure A-1 INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY,GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS E3RA R-Value Sieve Analysis Swell Test Cyclic Triaxial Unconsolidated Undrained Triaxial Torvane Shear Unconfined Compression (Shear Strength, ksf) Wash Analysis (with % Passing No. 200 Sieve) Water Level at Time of Drilling Water Level after Drilling(with date measured) RV SA SW TC TX TV UC (1.2) WA (20) Modified California Split Spoon Pushed Shelby Tube Auger Cuttings Grab Sample Sample Attempt with No Recovery Chemical Analysis Consolidation Compaction Direct Shear Permeability Pocket Penetrometer CA CN CP DS PM PP PtHIGHLY ORGANIC SOILS TYPICAL NAMES GRAVELS ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY, ORGANIC SILTS WELL GRADED GRAVELS, GRAVEL-SAND MIXTURES MAJOR DIVISIONS PEAT AND OTHER HIGHLY ORGANIC SOILS WELL GRADED SANDS, GRAVELLY SANDS POORLY GRADED SANDS, GRAVELLY SANDS SILTY SANDS, POOORLY GRADED SAND-SILT MIXTURES CLAYEY SANDS, POORLY GRADED SAND-CLAY MIXTURES POORLY GRADED GRAVELS, GRAVEL-SAND MIXTURES SOIL CLASSIFICATION CHART AND KEY TO TEST DATA GW GP GM GC SW SP SM SC ML FINE GRAINED SOILSMore than Half < #200 sieveLGD A NNNN02 GINT US LAB.GPJ 11/4/05INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS CL OL MH SANDS WITH OVER 15% FINES GB S-1 GBS-2 GP SM SM SM 0.5 3.5 4.5 7.5 (GP) Gray gravel with sand and some silt (medium dense, moist) (Gravel Surfacing) (SM) Brown silty sand (medium dense, moist) (Fill) (SM) Dark brown silty sand with logs, woody debris and general refuse (loose, moist) (Fill) (SM) Light brown silty sand with some gravel (medium dense, moist) (Weathered Till) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot.Bottom of test pit at 7.5 feet. NOTES GROUND ELEVATION LOGGED BY DMW EXCAVATION METHOD EXCAVATION CONTRACTOR GROUND WATER LEVELS: CHECKED BY DATE STARTED 1/21/15 COMPLETED 1/21/15 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZE SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 TEST PIT NUMBER TP-1 PAGE 1 OF 1 Figure A-2 CLIENT Totenham, LLC PROJECT NUMBER T15034 PROJECT NAME 701 Sunset Blvd NE PROJECT LOCATION Renton, Washington COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 4/3/15 16:53 - Z:\2015 JOB FILES\T15034 TOTENHAM, LLC - 701 NE SUNSET BLVD, RENTON GEOTECH\T15034 TEST PITS.GPJE3RA, Inc. E3RA, Inc. P.O. Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION GB S-1 GBS-2 GP SM SM SM 0.5 3.5 4.5 7.5 (GP) Gray gravel with sand and some silt (medium dense, moist) (Gravel Surfacing) (SM) Brown silty sand (medium dense, moist) (Fill) (SM) Dark brown silty sand with logs, woody debris and general refuse (loose, moist) (Fill) (SM) Light brown silty sand with some gravel (medium dense, moist) (Weathered Till) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot.Bottom of test pit at 7.5 feet. NOTES GROUND ELEVATION LOGGED BY DMW EXCAVATION METHOD EXCAVATION CONTRACTOR GROUND WATER LEVELS: CHECKED BY DATE STARTED 1/21/15 COMPLETED 1/21/15 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZE SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 TEST PIT NUMBER TP-2 PAGE 1 OF 1 Figure A-3 CLIENT Totenham, LLC PROJECT NUMBER T15034 PROJECT NAME 701 Sunset Blvd NE PROJECT LOCATION Renton, Washington COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 4/3/15 16:53 - Z:\2015 JOB FILES\T15034 TOTENHAM, LLC - 701 NE SUNSET BLVD, RENTON GEOTECH\T15034 TEST PITS.GPJE3RA, Inc. E3RA, Inc. P.O. Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION SM SM SM 0.5 3.5 4.5 7.5 Sod and Topsoil (SM) Brown silty sand (medium dense, moist) (Fill) (SM) Dark brown silty sand with logs, woody debris and general refuse (loose, moist) (Fill) (SM) Light brown silty sand with some gravel (medium dense, moist) (Weathered Till) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot.Bottom of test pit at 7.5 feet. NOTES GROUND ELEVATION LOGGED BY DMW EXCAVATION METHOD EXCAVATION CONTRACTOR GROUND WATER LEVELS: CHECKED BY DATE STARTED 1/21/15 COMPLETED 1/21/15 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZE SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 TEST PIT NUMBER TP-3 PAGE 1 OF 1 Figure A-4 CLIENT Totenham, LLC PROJECT NUMBER T15034 PROJECT NAME 701 Sunset Blvd NE PROJECT LOCATION Renton, Washington COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 4/3/15 16:53 - Z:\2015 JOB FILES\T15034 TOTENHAM, LLC - 701 NE SUNSET BLVD, RENTON GEOTECH\T15034 TEST PITS.GPJE3RA, Inc. E3RA, Inc. P.O. Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION