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Home My WebLink AboutA_GeotechnicalReport_15_1228_V1GEOTECHNICAL ENGINEERING EVALUATION GRANT'S PLACE RENTON, WASHINGTON PREPARED FOR TRIDOR, INC. N A 17311 —135'" Avenue NE, A-500 Woodinville, WA 98072 (425) 486-1669 . (425) Fax 481-2510 June 10, 2005 Mr. Scott Wiklof Tridor Inc. P.O. Box 747 Bellevue, WA 98009 NELSON GEOTECHNICAL ASSOCIATES, INC. GEOTECHNICAL ENGINEERS & GEOLOGISTS Geotechnical Engineering Evaluation Grant's Place Renton, Washington NGA File No. 712005 Dear Mr. Wiklof- Snohomish County (425) 337-1669 Wenatchee/Chelan (509) 7842756 We are pleased to submit the attached report titled "Geotechnical Engineering Evaluation — Grant's Place — Renton, Washington." This report summarizes the existing surface and subsurface conditions within the site and provides general recommendations for the proposed site development. Our services were completed in general accordance with the proposal signed by you on May 17, 2005. The site is currently occupied by a single-family residence and several outbuildings with brush and scattered trees within the western portion of the property. Development for this property is planned to consist of the construction of multiple three-story townhomes with associated pavement and utilities. Stormwater is to be managed on site via a detention system within the planned driveway access road. We monitored the excavation of eight test pits in the planned development areas. Our explorations indicated that the site is generally underlain by competent native glacial till deposits. The site is located in an area that was historically mined for coal. We did not observe evidence of mining operations such as mine shafts or tailings on this site. We also reviewed materials related to past coal mining activities in the site vicinity at the Washington State Department of Natural Resources. Based on our observations and the information we reviewed, it appears that mining operations were not specifically located on this site. We have concluded that the site is generally compatible with the planned development. We have recommended that the new structures be founded on the native medium dense or better soil for bearing capacity and settlement considerations. These soils should be encountered approximately one to two feet below the existing ground surface, based on our explorations. Minor to moderate amounts of groundwater were encountered within the upper soils in many of the test pits which may impact construction if earthwork activities take place during the wetter times of the year. Also, footing drains and other drainage systems should be incorporated into the design to control groundwater. In the attached report, we have also included general recommendations for site grading and drainage. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Summary - Page 2 It has been a pleasure to provide service to you on this project. Please contact us if you have any questions regarding this report or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Khale . Shawish, PE Principal Three Copies Submitted TABLE OF CONTENTS INTRODUCTION 1 SCOPE.........................................................................................................................................................1 SITECONDITIONS.................................................................................................................................. 2 SurfaceConditions.................................................................................................................................... 2 SubsurfaceConditions.............................................................................................................................. 2 HydrologicConditions.............................................................................................................................. 3 SENSITIVE AREA EVALUATION......................................................................................................... 3 SeismicHazard......................................................................................................................................... 3 ErosionHazard.......................................................................................................................................... 4 CONCLUSIONS AND RECOMMENDATIONS ................................................................................... 4 General...................................................................................................................................................... 4 Erosion Control Measures......................................................................................................................... 5 Temporary and Permanent Slopes............................................................................................................ 5 SitePreparation and Grading.................................................................................................................... 6 FoundationSupport ................................................................................................................................... 7 StructuralFill............................................................................................................................................ 8 Slab-on-Grade........................................................................................................................................... 9 Pavements............................................................................................................................................... 10 SiteDrainage........................................................................................................................................... 10 USEOF THIS REPORT..........................................................................................................................11 LIST OF FIGURES Figure 1 — Vicinity Map Figure 2 — Site Plan Figure 3 — Soil Classification Chart Figures 4 and 5 — Test Pit Logs NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington INTRODUCTION This report presents the results of our geotechnical engineering investigation and evaluation of the planned Grant's Place development in Renton, Washington. The project site is located at 1600 Grant Avenue South as shown on the Vicinity Map in Figure 1. The purpose of this study is to explore and characterize the site's surface and subsurface conditions and to provide geotechnical recommendations for site development. For our use in preparing this report, we have been provided with a site plan titled "Grant's Place," dated May 10, 2005, prepared by Kovach Architects. Development on the property will consist of the construction of 39 three-story, wood -framed townhome structures. A paved access driveway is planned for the middle of the property and will be accessed from Grant Avenue South on the western side of the property. Stormwater handling is planned to consist of an underground detention pipe or vault within the planned access road. The proposed site layout is shown on the Site Plan in Figure 2. SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions, and provide general recommendations for site development. Specifically, our scope of services includes the following: 1. Review existing soils, geologic, and coal mine maps of the area. 2. Explore the site subsurface soil and groundwater conditions with trackhoe-excavated test pits. Trackhoe was subcontracted by NGA. 3. Provide recommendations for site grading and earthwork, including structural fill. 4. Provide recommendations for foundation support and slabs -on -grade subgrade. 5. Provide recommendations for stormwater infiltration or detention system installations as needed. 6. Provide recommendations for site drainage and erosion control. 7. Provide recommendations for pavement subgrade preparation. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 2 8. Document the results of our explorations, findings, conclusions, and recommendations in a written geotechnical engineering report. SITE CONDITIONS Surface Conditions The site is an approximate 2.1 -acre, trapezoidal -shaped lot measuring approximately 621feet and 541 feet along the northern and southern property lines, respectively, and approximately 158 feet and 177 along the eastern and western property lines, respectively. The site is bounded to the east and south by residential properties, to the west by Grant Avenue South, and to the north by and undeveloped land. A single-family residence with a maintained grass lawn, scattered trees, and several outbuildings occupy the western portion of the property. The site is generally level with a slight gradient down to the west. An old shed, blackberry bushes, and scattered trees occupy the eastern half of the property. A small irrigation pond with a 3 -foot high retaining wall was observed within the eastern half of the site approximately 100 feet east of the residence and 75 feet north of the southern property line. Except for some water in the irrigation pond, we did not observe surface water on site during our visit on May 23, 2005. Subsurface Conditions Geology: The geologic units for this site are shown on the Geologic Map of the Renton Quadrangle, King County. Washington, by D. R. Mullineaux, (U.S.G.S., 1965). The site is mapped as Ground Moraine Deposits (Qgt) which is further described as two types of till with varying densities. The till deposits are described as an unsorted mixture of sand, silt, clay, and gravel. Our explorations generally encountered silty sand consistent with the description of the ablation till of the Ground Moraine Deposit. Explorations: The subsurface conditions within the site were explored on May 23, 2005 by excavating eight test pits to depths ranging from 4.5 to 8.5 feet below the existing surface using a trackhoe. The approximate locations of our explorations are shown on the Site Plan in Figure 2. A geologist from NGA was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the test pits. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 3 The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 3. The logs of our test pits are attached to this report and are presented as Figures 4 and 5. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions, the test pits logs should be reviewed. We encountered approximately 0.5 to 1.5 feet of loose topsoil at the surface in all of the test pits. Below the topsoil, we encountered medium dense to dense, orangish-brown to grayish -brown, silty, fine to medium sand with gravel, iron -oxide staining, and sand lenses. This soil was interpreted as glacial till. All test pits were terminated in the till deposit. Minor to moderate caving was encountered in most of the test pits. Hydrologic Conditions Minor to moderate groundwater seepage was encountered within all of the explorations at depths ranging from 2.5 to 7.5 feet below the existing ground surface. It is our opinion that this seepage is perched water. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of a relatively impermeable material such as the underlying silty sand. The more permeable soils consist of the topsoil and the upper weathered zone of the till. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched water to decrease during drier times of the year and increase during wetter periods. Due to the shallow occurrence of groundwater in our explorations and the relatively level ground surface, we anticipate that groundwater will be present on this site throughout the year. SENSITIVE AREA EVALUATION Seismic Hazard Medium dense to dense glacial soils were encountered underlying the site. Based on the 2003 International Building Code (IBC), the site conditions best fit the description for Soil Class D. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion by soft deposits. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. Ground motion amplification is caused by thick deposits of soft material. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 4 The medium dense to dense glacial till interpreted to underlie the site has a low potential for liquefaction or amplification of ground motion Erosion Hazard The erosion hazard criteria used for determination of affected areas includes soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey, King County Area, Washington, by the Soil Conservation Service (SCS) was reviewed to determine the erosion hazard of the on-site soils. The site surface soils were classified using the SCS classification system as Alderwood gravelly sandy loam, 6 to 15 percent slopes. This unit is listed as having a moderate erosion hazard. The site soils should have a low potential for erosion if not disturbed. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion, that from a geotechnical standpoint, the site is compatible with the planned development. Our explorations within the site indicated that the site is generally underlain by competent glacial till soils. These native soils should provide adequate support for the planned structure foundations, slab -on -grade, and pavement. We recommend that the buildings be designed utilizing shallow foundations. Footings should extend through any loose surficial soil or undocumented fill and be founded on the underlying medium dense or better native soils, or structural fill extending to these soils. Undocumented fill or loose soil could be encountered around the existing house and out buildings. Any undocumented fill or soft/loose soil should be over -excavated as part of site preparation. Coal mining has been conducted in the past in the general site vicinity. We did not observe mine shafts, tailings, or other indications of mining operations on this site. Also, information collected at the Washington State Department of Natural Resources did not indicate that mining operations were specifically conducted on this site. We should note, however, that the reviewed DNR maps for coal mine shafts and tunnels are based on old records that may not be entirely accurate. The soils that are expected to be encountered during site development are considered highly moisture - sensitive and can disturb in wet conditions. Wet soil and seeping water was observed in our explorations NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 5 at shallow depths. We recommend that the site be developed during the dry season. If construction takes place during the rainy months, the site soils may disturb and become difficult to work. Also, if construction takes place during the wet season, additional expenses and delays should be expected. Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades, construction traffic areas, and pavement areas prior to placing structural fill. NGA should be retained to determine if the on-site soils could be used as structural fill material during construction. We anticipate that wet conditions will be prevalent on this site throughout the year. We recommend that footing and wall drains as well as underslab drains be incorporated in the design. Also, cut-off or French - type drains might be needed at certain locations to maintain dry conditions. Erosion Control Measures The erosion hazard for the on-site soils is considered moderate, but will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Measures taken may include diverting surface water away from the stripped areas. Silt fences or straw bales should be erected to prevent muddy water from leaving the site. Temporary and Permanent Slopes We do not anticipate major grading on this site as part of site improvements, however, if an underground stormwater detention vault or a large detention pipe is used for handling stormwater runoff, temporary cuts over four feet in height may be needed for the installation of these systems. Temporary cut slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations since he is continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and groundwater conditions encountered. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 6 The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. For planning purposes, we recommend that temporary cuts in the native glacial till soils be no steeper than 1.5 Horizontal to 1 Vertical (1.5H: IV). If significant groundwater seepage or sandier portions of the till are encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. Measures taken may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHAIWISHA regulations. Site Preparation and Grading After the existing residence, trees, and ground cover have been removed, the next step of site preparation should be to strip any topsoil or loose material to expose medium dense or better native soils in foundation, pavement, and slab areas. Based on our observations, we anticipate an average stripping depth of the topsoil to be one to two feet across the site. However, additional stripping may be required in the vicinity of the existing residence and outbuildings, the pond, or in the unexplored areas where fill may exist. If the ground surface, after stripping the unsuitable material and excavating down to planned subgrade elevations appears to be loose, it should be compacted to a non -yielding condition and then proof -rolled with a heavy rubber -tired piece of equipment. Areas observed to pump or weave during the proof -roll test should be reworked to structural fill specifications or over -excavated and replaced with properly compacted structural fill or rock spalls. If significant surface water flow is encountered during construction, this flow should be diverted around areas to be developed and the exposed subgrade maintained in a semi -dry condition. After the water has been controlled, the site should be stripped and graded using large excavators equipped with wide tracks and smooth buckets. The exposed subgrade should not be compacted, as compaction of a wet subgrade may result in further disturbance of the native soils. Instead, a layer of crushed rock or all-weather material may be placed over the prepared areas to protect them from further disturbance. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 7 If a detention system is used, it should be excavated down to planned elevations while maintaining the recommended temporary excavation inclinations provided above. If groundwater seepage is encountered, this water should be pumped out of the excavation and the bottom of the excavation be covered with a minimum of six inches of crushed rock to reduce the potential for disturbing the sensitive subgrade and to provide a clean work surface for vault or pipe placement. As mentioned earlier, the site soils are considered highly moisture sensitive and can disturb when wet. We therefore recommend that construction take place in the summer during periods of extended dry weather, and suspended during periods of rainfall. If work is to take place during the wetter part of the year, care should be taken during site preparation not to disturb the site soils. This can be accomplished by utilizing large excavators equipped with smooth buckets and wide tracks to complete earthwork, and diverting surface and groundwater flow away from the prepared subgrades. Also, construction traffic should not be allowed on the exposed subgrade. A blanket of rock spalls should be used in construction access areas if wet conditions are prevalent. The thickness of this rock spall layer should be based on subgrade performance at the time of construction. For planning purposes, we recommend a minimum one -foot thick layer of rock spalls. Foundation Support Conventional shallow spread foundations for building support should be placed on undisturbed medium dense or better native soils or be supported on structural fill or rock spalls extending to those soils. Where less dense soils are encountered at footing bearing elevation, the subgrade should be over -excavated to expose suitable bearing soil. The over -excavation may be filled with structural fill, or the footing may be extended down to the bearing native soils. If footings are supported on structural fill, the fill zone should extend outside the edges of the footing a distance equal to one-half of the depth of the over -excavation below the bottom of the footing. Building footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Minimum foundation widths of 18 and 24 inches should be used for continuous and isolated footings, respectively, but footings should also be sized based on the anticipated loads and allowable soil bearing pressure. Standing water should not be allowed to NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 8 accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations constructed as outlined above, we recommend an allowable design bearing pressure of not more than 2,000 pounds per square foot (psf) be used for the building footing design for footings founded on the medium dense or better native soils or structural fill extending to the native competent material. The foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if higher bearing pressures are needed. Current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than one inch total and 1/2 inch differential between adjacent footings or across a distance of about 20 feet. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalent fluid density of 250 pounds per cubic foot (pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the fooling depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value of passive resistance, the foundations should be poured "neat" against the native medium dense to dense soils or compacted fill should be used as backfill against the front of the footing. We recommend that the upper one -foot of soil be neglected when calculating the passive resistance. Structural Fill General: Fill placed beneath foundations, pavement, or other settlement -sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in-place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fill NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 9 should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement Materials: Structural fill should consist of a good quality, granular soil, free of organics and other deleterious material and be well graded to a maximum size of about three inches. All-weather fill should contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing the U.S. 3/4 -inch sieve). The use of on-site soils as structural fill should generally be feasible, but will be dependent on material moisture content at the time construction takes place. Most of the on-site soils will be very difficult to compact to structural fill specifications in wet conditions. Even in dry weather, some moisture -conditioning of the on-site material might be required to attain compactable conditions. We should be retained to evaluate proposed structural fill material prior to construction. Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over - excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction. Slab -on -Grade Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. We recommend that all floor slabs be underlain by at least six inches of free -draining sand or gravel for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting (6 -mil minimum), should be placed over the capillary break material. Due to the wet site conditions, it might be prudent to utilize a system of underslab drains that are in turn routed to the perimeter drains, to further reduce the potential for groundwater to produce damp conditions in the dwellings. NELSON GEOTECHNICAL ASSOCIATES, INC, Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 10 Pavements Pavement subgrade preparation, and structural filling where required, should be completed as recommended in the Site Preparation and Grading and Structural 1311 subsections of this report. The pavement subgrade should be proof -rolled with a heavy, rubber -tired piece of equipment, to identify soft or yielding areas that require repair. We should be retained to observe the proof -rolling and recommend repairs prior to placement of the asphalt or hard surfaces. Site Drainage Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an appropriate stormwater collection system. Water should not be allowed to stand in any area where footings or slabs are to be constructed. Final site grades should allow for drainage away from the structures. We suggest that the finished ground be sloped at a minimum gradient of three percent, for a distance of at least 10 feet away from the structures. Surface water should be collected by permanent catch basins and drain lines, and be discharged into an appropriate discharge system. Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out of the excavation and routed into a permanent storm drain. We recommend the use of footing drains around the planned structure. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum four - inch -diameter, rigid, slotted or perforated, PVC pipe surrounded by free -draining material, such as washed rock, wrapped in a filter fabric. We recommend that an 18 -inch -wide zone of clean (less than three -percent fines), granular material be placed along the back of the walls above the drain. Pea gravel is an acceptable drain material or drainage composite may also be used instead. The free -draining material should extend up the wall to one foot below the finished surface. The top foot of backfill should consist of impermeable soil placed over plastic sheeting or building paper to minimize surface water or fines migration into the footing drain. Footing drains should discharge into tightlines leading to an appropriate collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to footing drains. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 11 Due to prevalent wet site conditions, cut-off or French -type drains may be required uphill of the planned improvements to control groundwater and maintain semi -dry pads. The need and extent of such systems should be determined in the field prior to the start of mass grading. Also, underslab drains might be considered for this site. The underslab drain systems usually consist of 4 -inch perforated lateral pipes placed within the capillary break layer, 10 to 15 feet apart. The laterals are routed to a solid main collector drain that in turn is routed into the footing drain system. We should be retained to review plans for site drainage. USE OF THIS REPORT NGA has prepared this report for Tridor Inc., and their agents, for use in the planning and design of the development planned on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. There are possible variations in subsurface conditions between the explorations and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. We should be contacted a minimum of one week prior to construction activities and could attend pre -construction meetings if requested. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at the time this report was prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. E•• NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Grant's Place Renton, Washington June 10, 2005 NGA File No. 712005 Page 12 It has been a pleasure to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Bala Dodoye-Alah Project Geologist n k.t s EXPIRES ....:- Khaled M. Shawish, PE Principal I1071MLTJ MFTi1 Five Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. II_ NOT TO SCALE Project Number NELSON GEOTECHNICy AL No. Date Revision ay CK 712005 Grants Place /SGA ASSOCIATES, INC. 1 5/24105 Original ACO BAD a GEOTECHNICAL ENGINEERS & GEOLOGISTS Figure 1 Vicinity Map � ti91 t-iffiN Mn. NE,A6fa WMOMe�Cw�q (4ffi 93I -tom 0 W¢dti�9eWR9BS13 e�a�dCMan 15W X3]55 (4L51456i859/Fei48'IR510 .igson (a_9 \ \ 10 20 Reference: Site Plan based on an electronic plan dated May 25, 2005, titled "Grant's Place," prepared by Kovach Architects. UNIFIED SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS GROUP NAME SYMBOL CLEAN GW WELL -GRADED, FINE TO COARSE GRAVEL COARSE- GRAVEL GRAVEL GP POORLY -GRADED GRAVEL GRAINED MORE THAN 50 % GRAVEL GM OF COARSE FRACTION SILTY GRAVEL RETAINED ON SOILS NO. 4SIEVE WITH FINES GC CLAYEY GRAVEL SAND CLEAN SW WELL -GRADED SAND, FINE TO COARSE SAND SAND SP POORLY GRADED SAND MORE THAN 50 % RETAINED ON MORE THAN 50 % NO. 200 SIEVE OF COARSE FRACTION SAND SM SILTY SAND PASSES NO. 4 SIEVE WITH FINES SC CLAYEY SAND FINE - SILT AND CLAY ML SILT INORGANIC GRAINED LIQUID LIMIT CL CLAY LESS THAN 50 % SOILS ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILT AND CLAY MH SILT OF HIGH PLASTICITY, ELASTIC SILT INORGANIC MORE THAN 50 °k PASSES LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FLAT CLAY NO. 200 SIEVE 50 % OR MORE ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1) Field classification is based on visual SOIL MOISTURE MODIFIERS: examination of soil in general accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to the touch 2) Soil classification using laboratory tests is based on ASTM D 2488-93. Moist -Damp, but no visible water. 3) Descriptions of soil density or Wet -Visible free water or saturated, consistency are based on usually soil is obtained from interpretation of blowcount data, below water table visual appearance of soils, and/or test data. Project Number NELSON GEOTECHNICAL No. Date Revision By CK 712005 Grant's Place )yam - GA ASSOCIATES, INC. Soil Classification GEOTECHNICAL ENGINEERS a: GEOLOGISTS , 5124/05 Original Aco eno Figure 3 ii311-1361M1Mo. NE.pfial 8i 1pnvli Cmnb H�51�6180]-ip9 WmimiN. WA�1P1 Ware,tleM:haYn (VSfiffi1668/Fa[LBt-1610 ¢�Np oreAamn�� LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION TEST PIT ONE 1.0-2.5 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND (MEDIUM DENSE, MOIST TO WET) 0.0-1.0 SM GRAYISH -BROWN, SILTY FINE TO MEDIUM SAND (DENSE, MOIST TO WET) TOPSOIL (LOOSE, MOIST) 1.0-2.5 SM ORANGISH-BROWN TO BROWN, SILTY FINE TO COARSE SAND (MEDIUM DENSE, MOIST) 2.5-7.0 SM ORANGISH-BROWN TO BROWN, SILTY FINE TO COARSE SAND WITH GRAVEL AND TEST PIT WAS COMPLETED AT 7.0 FEET ON 5/23/05 COBBLES (DENSE, MOIST) 7.0-8.5 SP -SM GRAY, FINE TO MEDIUM SAND WITH SILT ANDGRAVEL (DENSE, WET) SAMPLE WAS COLLECTED AT 4.5 FEET MINOR GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 7.5 FEET MINOR TEST PIT CAVING WAS ENCOUNTERED FROM 7.0 TO 8.5 FEET TEST PIT WAS COMPLETED AT 8.5 FEET ON 5/23/05 TEST PIT TWO 0.0-0.5 TOPSOIL WITH ROOTS (LOOSE, MOIST) 0.5-2.0 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE, MOIST) 2.0-7.0 SM GRAY, SILTY FINE TO COARSE SAND WITH GRAVEL (DENSE TO VERY DENSE, MOIST) SAMPLE WAS COLLECTED AT 3.2 FEET MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 6.5 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 7.0 FEET ON 5/23/05 TEST PIT THREE 0.0-1.0 TOPSOIL (LOOSE, MOIST) 1.0-2.5 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND (MEDIUM DENSE, MOIST TO WET) 2.5-7.0 SM GRAYISH -BROWN, SILTY FINE TO MEDIUM SAND (DENSE, MOIST TO WET) 2.5-4.5 SAMPLE WAS COLLECTED AT 2.0 FEET MINOR TO MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 3.0 FEET MINOR TEST PIT CAVING WAS ENCOUNTERED FROM 6.0 TO 7.5 FEET TEST PIT WAS COMPLETED AT 7.0 FEET ON 5/23/05 TEST PIT FOUR 0.0-1.0 TOPSOIL (LOOSE, MOIST) 1.0-2.5 SM ORANGE, SILTY FINE TO MEDIUM SAND WITH GRAVEL (LOOSE TO MEDIUM DENSE, MOIST TO WET) 2.5-4.5 SM ORANGISH-BROWN, SILTY FINE TO COARSE SAND WITH GRAVEL (DENSE, MOIST) SAMPLES WERE NOT COLLECTED MINOR TO MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 2.5 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 4.5 FEET ON 5/23/05 ACO: BAD NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 712005 FIGURE 4 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION TEST PIT FIVE 0.0-1.2 TOPSOIL (LOOSE, MOIST) 1.2-5.0 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE, MOIST TO WET) 5.0-6.0 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND WITH SILT LAYERS AND IRON -OXIDE STAINING (DENSE, MOIST) SAMPLES WERE COLLECTED AT 3.0 ND 6.0 FEET MINOR TO MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED FROM 2.5 TO 6.0 FEET MINOR TEST PIT CAVING WAS ENCOUNTERED FROM 0.0 TO 6.0 FEET TEST PIT WAS COMPLETED AT 6.0 FEET ON 5/23/05 TEST PIT SIX 0.0-1.0 TOPSOIL (LOOSE, MOIST) 1.0-3.0 SM ORANGISH-BROWN, SLTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE, MOIST) 3.0-5.0 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND WITH IRON -OXIDE STAINING (MEDIUM DENSE, MOIST TO WET) SAMPLES WERE NOT COLLECTED MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 3.0 FEET MINOR TEST PIT CAVING WAS ENCOUNTERED FROM 4.0 TO 5.0 FEET TEST PIT WAS COMPLETED AT 5.0 FEET ON 5/23/05 TEST PIT SEVEN 0.0-1.0 TOPSOIL (LOOSE, MOIST) 1.0-2.5 SM ORANGE, SILTY FINE TO MEDIUM SAND WITH ROOTS (MEDIUM DENSE, MOIST) 2.5-6.5 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND IRON -OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST) SAMPLE WAS COLLECTED AT 4.0 FEET MINOR GROUNDWATER SEEPAGE WAS ENCOUNTERED FROM 2.0 TO 6.5 FEET MINOR TEST PIT CAVING WAS ENCOUNTERED FROM 2.5 TO 6.5 FEET TEST PIT WAS COMPLETED AT 6.5 FEET ON 5/23/05 TEST PIT EIGHT 0.0-1.5 TOPSOIL WITH ROOTS (LOOSE, MOIST) 1.5-6.0 SM ORANGISH-BROWN, SILTY FINE TO MEDIUM SAND WITH SILT LAYERS AND IRON -OXIDE STAINING (MEDIUM DENSE, MOIST TO WET) SAMPLES WERE COLLECTED AT 2.0 AND 6.0 FEET MINOR GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 4.5 FEET MINOR TEST PIT CAVING WAS ENCOUNTERED FROM 4.5 TO 5.0 FEET TEST PIT WAS COMPLETED AT 6.0 FEET ON 5/23/05 ACO:BAD NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 712005 FIGURE 5