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Home My WebLink AboutRS_Geotechnical_Engineering_Report_Genesis_Homes_LLC_200130_v1 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 ♦ Fax 425.415.0311 www.riley-group.com GEOTECHNICAL ENGINEERING REPORT PREPARED BY: THE RILEY GROUP, INC. 17522 BOTHELL WAY NORTHEAST BOTHELL, WASHINGTON 98011 PREPARED FOR: GENESIS HOMES, LLC 16220 NE 3RD AVENUE BELLEVUE, WASHINGTON 98008 RGI PROJECT NO. 2019-092 GENESIS HOMES RENTON 1501 - 1507 KIRKLAND AVENUE NORTHEAST RENTON, WASHINGTON MAY 17, 2019 Geotechnical Engineering Report i May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 TABLE OF CONTENTS 1.0 INTRODUCTION ............................................................................................................................... 1 2.0 PROJECT DESCRIPTION ............................................................................................................... 1 3.0 FIELD EXPLORATION AND LABORATORY TESTING .......................................................... 1 3.1 FIELD EXPLORATION ................................................................................................................................... 1 3.2 LABORATORY TESTING ................................................................................................................................ 2 4.0 SITE CONDITIONS ........................................................................................................................... 2 4.1 SURFACE .................................................................................................................................................. 2 4.2 GEOLOGY ................................................................................................................................................. 2 4.3 SOILS ....................................................................................................................................................... 2 4.4 GROUNDWATER ........................................................................................................................................ 3 4.5 SEISMIC CONSIDERATIONS ........................................................................................................................... 3 4.6 GEOLOGIC HAZARD AREAS .......................................................................................................................... 4 5.0 DISCUSSION AND RECOMMENDATIONS ................................................................................. 4 5.1 GEOTECHNICAL CONSIDERATIONS ................................................................................................................. 4 5.2 EARTHWORK ............................................................................................................................................. 4 5.2.1 Erosion and Sediment Control ..................................................................................................... 4 5.2.2 Stripping and Subgrade Preparation ............................................................................................ 5 5.2.3 Excavations................................................................................................................................... 5 5.2.4 Structural Fill ................................................................................................................................ 6 5.2.5 Wet Weather Construction Considerations ................................................................................. 8 5.3 FOUNDATIONS .......................................................................................................................................... 8 5.4 RETAINING WALLS ..................................................................................................................................... 9 5.5 SLAB-ON-GRADE CONSTRUCTION ............................................................................................................... 10 5.6 DRAINAGE .............................................................................................................................................. 10 5.6.1 Surface ....................................................................................................................................... 10 5.6.2 Subsurface .................................................................................................................................. 10 5.6.3 Infiltration .................................................................................................................................. 10 5.7 UTILITIES ................................................................................................................................................ 11 6.0 ADDITIONAL SERVICES .............................................................................................................. 11 7.0 LIMITATIONS ................................................................................................................................. 11 LIST OF FIGURES AND APPENDICES Figure 1 ..................................................................................................................... Site Vicinity Map Figure 2 ............................................................................................... Geotechnical Exploration Plan Figure 3 ............................................................................................... Retaining Wall Drainage Detail Figure 4 ....................................................................................................Typical Footing Drain Detail Appendix A .......................................................................... Field Exploration and Laboratory Testing Geotechnical Engineering Report ii May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 Executive Summary This Executive Summary should be used in conjunction with the entire Geotechnical Engineering Report (GER) for design and/or construction purposes. It should be recognized that specific details were not included or fully developed in this section, and the GER must be read in its entirety for a comprehensive understanding of the items contained herein. Section 7.0 should be read for an understanding of limitations. RGI’s geotechnical scope of work included the advancement of 3 test pits to approximate depths of 10 feet below existing site grades. Based on the information obtained from our subsurface exploration, the site is suitable for development of the proposed project. The following geotechnical considerations were identified: Soil Conditions: The soils encountered during field exploration include loose to medium dense silty sand with trace to some gravel, over dense sand with some silt and trace gravel. Groundwater: No groundwater seepage was encountered during our subsurface exploration. Foundations: Foundations for the proposed building may be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab-on-grade: Slab-on-grade floors and slabs for the proposed building can be supported on medium dense to dense native soil or structural fill. Geotechnical Engineering Report 1 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 1.0 Introduction This Geotechnical Engineering Report (GER) presents the results of the geotechnical engineering services provided for the Genesis Homes Renton in Renton, Washington. The purpose of this evaluation is to assess subsurface conditions and provide geotechnical recommendations for the construction of new single family residences. Our scope of services included field explorations, laboratory testing, engineering analyses, and preparation of this GER. The recommendations in the following sections of this GER are based upon our current understanding of the proposed site development as outlined below. If actual features vary or changes are made, RGI should review them in order to modify our recommendations as required. In addition, RGI requests to review the site grading plan, final design drawings and specifications when available to verify that our project understanding is correct and that our recommendations have been properly interpreted and incorporated into the project design and construction. 2.0 Project description The project site is located at 1501 - 1507 Kirkland Avenue Northeast in Renton, Washington. The approximate location of the site is shown on Figure 1. The site is currently occupied by two single family residences, along Kirkland Avenue Northeast, with associated outbuildings. RGI understands that the current structures will be demolished for new single family residences. Stormwater infiltration on part of the site is also being considered. At the time of preparing this GER, building plans were not available for our review. Based on our experience with similar construction, RGI anticipates that the proposed building will be supported on perimeter walls with bearing loads of two to six kips per linear foot, and a series of columns with a maximum load up to 30 kips. Slab-on-grade floor loading of 250 pounds per square foot (psf) are expected. 3.0 Field Exploration and Laboratory Testing 3.1 FIELD EXPLORATION On May 2, 2019, RGI observed the excavation of 3 test pits. The approximate exploration locations are shown on Figure 2. Field logs of each exploration were prepared by the geologist that continuously observed the excavation. These logs included visual classifications of the materials encountered during excavation as well as our interpretation of the subsurface conditions between samples. The test pits logs included in Appendix A, represent an interpretation of the field Geotechnical Engineering Report 2 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 logs and include modifications based on laboratory observation and analysis of the samples. 3.2 LABORATORY TESTING During the field exploration, a representative portion of each recovered sample was sealed in containers and transported to our laboratory for further visual and laboratory examination. Selected samples retrieved from the test pits and hand auger were tested for moisture content and grain size analysis to aid in soil classification and provide input for the recommendations provided in this GER. The results and descriptions of the laboratory tests are enclosed in Appendix A. 4.0 Site Conditions 4.1 SURFACE The subject site is a rectangular-shaped parcel of land approximately 0.5 acres in size. The site is bound to the north, south, and west by residential property, and to the east by Kirkland Avenue Northeast. The existing site is two single family residences with outbuildings, and covered by trees and grass. The yards contain a few trees and bushes but are mostly grass or gravel. The site is relatively flat with an overall elevation difference of approximately 5 feet. 4.2 GEOLOGY Review of the Preliminary Geologic Map of Seattle and vicinity, Washington, by H. H. Waldron, etc. (1962) indicates that the soil in the project vicinity is mapped as Vashon till (Qt), which is light to dark gray, nonsorted, nonstratified mixture of clay, silt, sand, and gravel. The deposit is generally very stiff and impermeable, often resulting in poorly drained bogs developing in relatively flat area. The deposit is usually 1 to 2 meters thick, but locally can be as much as 25 meters. These descriptions are generally similar to the findings in our field explorations. 4.3 SOILS The soils encountered during field exploration include medium dense silty sand with trace gravel over dense sand with silt. More detailed descriptions of the subsurface conditions encountered are presented in the test pits logs included in Appendix A. Sieve analysis was performed on two selected soil samples. Grain size distribution curves are included in Appendix A. Geotechnical Engineering Report 3 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 4.4 GROUNDWATER No groundwater seepage was encountered during our subsurface exploration. It should be recognized that fluctuations of the groundwater table will occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the explorations were performed. In addition, perched water can develop within seams and layers contained in fill soils or higher permeability soils overlying less permeable soils following periods of heavy or prolonged precipitation. Therefore, groundwater levels during construction or at other times in the future may be higher or lower than the levels indicated on the logs. Groundwater level fluctuations should be considered when developing the design and construction plans for the project. 4.5 SEISMIC CONSIDERATIONS Based on the 2015 International Building Code (IBC), RGI recommends the follow seismic parameters for design. Table 1 2015 IBC Parameter Value Site Soil Class1 D2 Site Latitude 47.506044° N Site Longitude 122.178948° W Short Period Spectral Response Acceleration, SS (g) 1.426 1-Second Period Spectral Response Acceleration, S1 (g) 0.537 Adjusted Short Period Spectral Response Acceleration, SMS (g) 1.426 Adjusted 1-Second Period Spectral Response Acceleration, SM1 (g) 0.805 1. Note: In general accordance with Chapter 20 of ASCE 7-10. The Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile. 2. Note: The 2015 IBC and ASCE 7-10 require a site soil profile determination extending to a depth of 100 feet for seismic site classification. The current scope of our services does not include the required 100 foot soil profile determination. Test pits extended to a maximum depth of 10 feet, and this seismic site class definition considers that similar soil continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions below the current depth of exploration. Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations from a seismic event. Liquefaction mainly affects geologically recent deposits of fine-grained sands that are below the groundwater table. Soils of this nature derive their strength from intergranular friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction, thus reducing or eliminating the soil’s strength. Geotechnical Engineering Report 4 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 RGI reviewed the results of the field and laboratory testing and assessed the potential for liquefaction of the site’s soil during an earthquake. Since the site is underlain by glacially consolidated deposits, RGI considers that the possibility of liquefaction during an earthquake is minimal. 4.6 GEOLOGIC HAZARD AREAS Regulated geologically hazardous areas include erosion, landslide, earthquake, or other geological hazards. Based on the definition in the Renton Municipal Code, the site does not contain geologically hazardous areas. 5.0 Discussion and Recommendations 5.1 GEOTECHNICAL CONSIDERATIONS Based on our study, the site is suitable for the proposed construction from a geotechnical standpoint. Foundations for the proposed building can be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab-on- grade floors and pavements can be similarly supported. Detailed recommendations regarding the above issues and other geotechnical design considerations are provided in the following sections. These recommendations should be incorporated into the final design drawings and construction specifications. 5.2 EARTHWORK The earthwork is expected to include excavating and backfilling the building foundations and preparing slab subgrades. 5.2.1 EROSION AND SEDIMENT CONTROL Potential sources or causes of erosion and sedimentation depend on construction methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. The impacts on erosion-prone areas can be reduced by implementing an erosion and sedimentation control plan. The plan should be designed in accordance with applicable city and/or county standards. RGI recommends the following erosion control Best Management Practices (BMPs):  Scheduling site preparation and grading for the drier summer and early fall months and undertaking activities that expose soil during periods of little or no rainfall  Retaining existing vegetation whenever feasible  Establishing a quarry spall construction entrance  Installing siltation control fencing or anchored straw or coir wattles on the downhill side of work areas Geotechnical Engineering Report 5 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092  Covering soil stockpiles with anchored plastic sheeting  Revegetating or mulching exposed soils with a minimum 3-inch thickness of straw if surfaces will be left undisturbed for more than one day during wet weather or one week in dry weather  Directing runoff away from exposed soils and slopes  Minimizing the length and steepness of slopes with exposed soils and cover excavation surfaces with anchored plastic sheeting  Decreasing runoff velocities with check dams, straw bales or coir wattles  Confining sediment to the project site  Inspecting and maintaining erosion and sediment control measures frequently (The contractor should be aware that inspection and maintenance of erosion control BMPs is critical toward their satisfactory performance. Repair and/or replacement of dysfunctional erosion control elements should be anticipated.) Permanent erosion protection should be provided by reestablishing vegetation using hydroseeding and/or landscape planting. Until the permanent erosion protection is established, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. 5.2.2 STRIPPING AND SUBGRADE PREPARATION Stripping efforts should include removal of pavements, vegetation, organic materials, and deleterious debris from areas slated for building, pavement, and utility construction. The test pits encountered 6 to 8 inches of topsoil and rootmass. Deeper areas of stripping may be required in heavily vegetated areas of the site. Subgrade soils that become disturbed due to elevated moisture conditions should be overexcavated to reveal firm, non-yielding, non-organic soils and backfilled with compacted structural fill. In order to maximize utilization of site soils as structural fill, RGI recommends that the earthwork portion of this project be completed during extended periods of warm and dry weather if possible. If earthwork is completed during the wet season (typically November through May) it will be necessary to take extra precautionary measures to protect subgrade soils. Wet season earthwork will require additional mitigative measures beyond that which would be expected during the drier summer and fall months. 5.2.3 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consist of medium dense silty sand with trace gravel over dense glacial till. Geotechnical Engineering Report 6 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the temporary side slopes should be laid back with a minimum slope inclination of 1H:1V (Horizontal:Vertical). If there is insufficient room to complete the excavations in this manner, or excavations greater than 20 feet in depth are planned, using temporary shoring to support the excavations should be considered. For open cuts at the site, RGI recommends:  No traffic, construction equipment, stockpiles or building supplies are allowed at the top of cut slopes within a distance of at least five feet from the top of the cut  Exposed soil along the slope is protected from surface erosion using waterproof tarps and/or plastic sheeting  Construction activities are scheduled so that the length of time the temporary cut is left open is minimized  Surface water is diverted away from the excavation  The general condition of slopes should be observed periodically by a geotechnical engineer to confirm adequate stability and erosion control measures In all cases, however, appropriate inclinations will depend on the actual soil and groundwater conditions encountered during earthwork. Ultimately, the site contractor must be responsible for maintaining safe excavation slopes that comply with applicable OSHA or WISHA guidelines. 5.2.4 STRUCTURAL FILL RGI recommends fill below the foundation and floor slab, behind retaining walls, and below pavement and hardscape surfaces be placed in accordance with the following recommendations for structural fill. The structural fill should be placed after completion of site preparation procedures as described above. The suitability of excavated site soils and import soils for compacted structural fill use will depend on the gradation and moisture content of the soil when it is placed. 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. Soils containing more than about 5 percent fines cannot be consistently compacted to a dense, non-yielding condition when the moisture content is more than 2 percent above or below optimum. Optimum moisture content is that moisture that results in the greatest compacted dry density with a specified compactive effort. Non-organic site soils are only considered suitable for structural fill provided that their moisture content is within about two percent of the optimum moisture level as determined by ASTM D1557. Excavated site soils may not be suitable for re-use as structural fill depending on the moisture content and weather conditions at the time of construction. If soils are stockpiled for future reuse and wet weather is anticipated, the stockpile should be Geotechnical Engineering Report 7 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 protected with plastic sheeting that is securely anchored. Even during dry weather, moisture conditioning (such as, windrowing and drying) of site soils to be reused as structural fill may be required. Even during the summer, delays in grading can occur due to excessively high moisture conditions of the soils or due to precipitation. If wet weather occurs, the upper wetted portion of the site soils may need to be scarified and allowed to dry prior to further earthwork, or may need to be wasted from the site. The site soils are moisture sensitive and may require moisture conditioned prior to use as structural fill. If on-site soils are or become unusable, it may become necessary to import clean, granular soils to complete site work that meet the grading requirements listed in Table 2 to be used as structural fill. Table 2 Structural Fill Gradation U.S. Sieve Size Percent Passing 4 inches 100 No. 4 sieve 22 to 100 No. 200 sieve 0 to 5* *Based on minus 3/4 inch fraction. Prior to use, an RGI representative should observe and test all materials imported to the site for use as structural fill. Structural fill materials should be placed in uniform loose layers not exceeding 12 inches and compacted as specified in Table 3. The soil’s maximum density and optimum moisture should be determined by ASTM D1557. Table 3 Structural Fill Compaction ASTM D1557 Location Material Type Minimum Compaction Percentage Moisture Content Range Foundations On-site granular or approved imported fill soils: 95 +2 -2 Retaining Wall Backfill On-site granular or approved imported fill soils: 92 +2 -2 Slab-on-grade On-site granular or approved imported fill soils: 95 +2 -2 General Fill (non- structural areas) On-site soils or approved imported fill soils: 90 +3 -2 Pavement – Subgrade and Base Course On-site granular or approved imported fill soils: 95 +2 -2 Geotechnical Engineering Report 8 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 Placement and compaction of structural fill should be observed by RGI. A representative number of in-place density tests should be performed as the fill is being placed to confirm that the recommended level of compaction is achieved. 5.2.5 WET WEATHER CONSTRUCTION CONSIDERATIONS RGI recommends that preparation for site grading and construction include procedures intended to drain ponded water, control surface water runoff, and to collect shallow subsurface seepage zones in excavations where encountered. It will not be possible to successfully compact the subgrade or utilize on-site soils as structural fill if accumulated water is not drained prior to grading or if drainage is not controlled during construction. Attempting to grade the site without adequate drainage control measures will reduce the amount of on-site soil effectively available for use, increase the amount of select import fill materials required, and ultimately increase the cost of the earthwork phases of the project. Free water should not be allowed to pond on the subgrade soils. RGI anticipates that the use of berms and shallow drainage ditches, with sumps and pumps in utility trenches, will be required for surface water control during wet weather and/or wet site conditions. 5.3 FOUNDATIONS Following site preparation and grading, the proposed building foundation can be supported on conventional spread footings bearing on dense native soil or structural fill. Loose, organic, or other unsuitable soils may be encountered in the proposed building footprint. If unsuitable soils are encountered, they should be overexcavated and backfilled with structural fill. If loose soils granular soils are encountered, the soil should be moisture conditioned and compacted to the requirements of structural fill. Table 4 Foundation Design Design Parameter Value Allowable Bearing Capacity - Structural Fill Dense native soils 2,500 psf1 4,000 psf Friction Coefficient 0.30 Passive pressure (equivalent fluid pressure) 250 pcf2 Minimum foundation dimensions Columns: 24 inches Walls: 16 inches 1. psf = pounds per square foot 2. pcf = pounds per cubic foot The allowable foundation bearing pressures apply to dead loads plus design live load conditions. For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity may be used. At perimeter locations, RGI recommends not including the upper 12 Geotechnical Engineering Report 9 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 inches of soil in the computation of passive pressures because they can be affected by weather or disturbed by future grading activity. The passive pressure value assumes the foundation will be constructed neat against competent soil or backfilled with structural fill as described in Section 5.2.5. The recommended base friction and passive resistance value includes a safety factor of about 1.5. Perimeter foundations exposed to weather should be at a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. Finished grade is defined as the lowest adjacent grade within 5 feet of the foundation for perimeter (or exterior) footings and finished floor level for interior footings. With spread footing foundations designed in accordance with the recommendations in this section, maximum total and differential post-construction settlements of 1 inch and 1/2 inch, respectively, should be expected. 5.4 RETAINING WALLS If retaining walls are needed in the building area or for vaults, RGI recommends cast-in- place concrete walls be used. The magnitude of earth pressure development on retaining walls will partly depend on the quality of the wall backfill. RGI recommends placing and compacting wall backfill as structural fill. Wall drainage will be needed behind the wall face. A typical retaining wall drainage detail is shown in Figure 3. With wall backfill placed and compacted as recommended, and drainage properly installed, RGI recommends using the values in the following table for design. Table 5 Retaining Wall Design Design Parameter Value Allowable Bearing Capacity - Structural Fill Dense native soils 2,500 psf 4,000 psf Active Earth Pressure (unrestrained walls) 35 pcf At-rest Earth Pressure (restrained walls) 50 pcf For seismic design, an additional uniform load of 7 times the wall height (H) for unrestrained walls and 14H in psf for restrained walls should be applied to the wall surface. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 5.3. Geotechnical Engineering Report 10 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 5.5 SLAB-ON-GRADE CONSTRUCTION Once site preparation has been completed as described in Section 5.2, suitable support for slab-on-grade construction should be provided. RGI recommends that the concrete slab be placed on top of medium dense native soil or structural fill. Immediately below the floor slab, RGI recommends placing a four-inch thick capillary break layer of clean, free-draining sand or gravel that has less than five percent passing the U.S. No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. Where moisture by vapor transmission is undesirable, an 8- to 10-millimeter thick plastic membrane should be placed on a 4-inch thick layer of clean gravel. For the anticipated floor slab loading, we estimate post-construction floor settlements of 1/4- to 1/2-inch. 5.6 DRAINAGE 5.6.1 SURFACE Final exterior grades should promote free and positive drainage away from the building area. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building area. For non-pavement locations, RGI recommends providing a minimum drainage gradient of 3 percent for a minimum distance of 10 feet from the building perimeter. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. 5.6.2 SUBSURFACE RGI recommends installing perimeter foundation drains. A typical footing drain detail is shown on Figure 4. The foundation drains and roof downspouts should be tightlined separately to an approved discharge facility. Subsurface drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. 5.6.3 INFILTRATION RGI understands that an infiltration system is being considered for the on-site disposal of storm water run-off. A field infiltration test at test pit TP-2 was performed in general accordance with a Small-Scale Pilot Infiltration Test described in the 2017 City of Renton Surface Water Design Manual (CRSWDM). Geotechnical Engineering Report 11 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 Table 6 Measured Infiltration Rates Test Location Test Depth Measured Rate (Inches per hour) Design Rate (Inches per hour) TP-2 6’ 2.8 1.1 CRSWDM correction factors were applied to the field measured rate of 2.8 inches per hour. No groundwater was encountered in the test pits. Idesign = Imeasured x Ftesting x Fplugging x Fgeometry Correction factors of 0.5 (Ftesting) for the PIT test method and 0.8 (Fplugging) for fine sands were applied to the field measured rate to estimate the long-term design infiltration rate. We assumed Fgeometry = 1. The application of the correction factors yield a long-term design rate (Idesign) of 1.1 inches per hour. 5.7 UTILITIES Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) specifications. For site utilities located within the right-of-ways, bedding and backfill should be completed in accordance with City of Renton specifications. At a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.2.4. Where utilities occur below unimproved areas, the degree of compaction can be reduced to a minimum of 90 percent of the soil’s maximum density as determined by the referenced ASTM D1557. As noted, soils excavated on site may not be suitable for use as backfill material. Imported structural fill meeting the gradation provided in Table 2 should be used for trench backfill. 6.0 Additional Services RGI is available to provide further geotechnical consultation throughout the design phase of the project. RGI should review the final design and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and incorporated into project design and construction. RGI is also available to provide geotechnical engineering and construction monitoring services during construction. The integrity of the earthwork and construction depends on proper site preparation and procedures. In addition, engineering decisions may arise in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this scope of work. 7.0 Limitations This GER is the property of RGI, Genesis Homes, LLC, and its designated agents. Within the limits of the scope and budget, this GER was prepared in accordance with generally Geotechnical Engineering Report 12 May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 accepted geotechnical engineering practices in the area at the time this GER was issued. This GER is intended for specific application to the Genesis Homes Renton project in Renton, Washington, and for the exclusive use of Genesis Homes, LLC and its authorized representatives. No other warranty, expressed or implied, is made. Site safety, excavation support, and dewatering requirements are the responsibility of others. The scope of services for this project does not include either specifically or by implication any environmental or biological (for example, mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, we can provide a proposal for these services. The analyses and recommendations presented in this GER are based upon data obtained from the explorations performed on site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, RGI should be requested to reevaluate the recommendations in this GER prior to proceeding with construction. It is the client’s responsibility to see that all parties to the project, including the designers, contractors, subcontractors, are made aware of this GER in its entirety. The use of information contained in this GER for bidding purposes should be done at the contractor’s option and risk. USGS, 2014, Mercer Island, Washington USGS, 2014, Renton, Washington 7.5-Minute Quadrangle Approximate Scale: 1"=1000' 0 500 1000 2000 N Site Vicinity Map Figure 1 05/2019 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Genesis Homes Renton RGI Project Number: 2019-092 Date Drawn: Address: 1501 Kirkland Avenue Northeast, Renton, Washington 98056 SITE TP-1 TP-2/ IT-1 TP-3 N Geotechnical Exploration Plan Figure 2 Approximate Scale: 1"=40' 0 20 40 80 = Test pit by RGI, 5/2/19 = Site boundary 05/2019 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Genesis Homes Renton RGI Project Number: 2019-092 Date Drawn: Address: 1501 Kirkland Avenue Northeast, Renton, Washington 98056 Incliniations) 12" Over the Pipe 3" Below the Pipe Perforated Pipe 4" Diameter PVC Compacted Structural Backfill (Native or Import) 12" min. Filter Fabric Material 12" Minimum Wide Free-Draining Gravel Slope to Drain (See Report for Appropriate Excavated Slope 05/2019 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Genesis Homes Renton RGI Project Number: 2019-092 Date Drawn: Address: 1501 Kirkland Avenue Northeast, Renton, Washington 98056 Retaining Wall Drainage Detail Figure 3 Not to Scale 3/4" Washed Rock or Pea Gravel 4" Perforated Pipe Building Slab Structural Backfill Compacted Filter Fabric 05/2019 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Genesis Homes Renton RGI Project Number: 2019-092 Date Drawn: Address: 1501 Kirkland Avenue Northeast, Renton, Washington 98056 Typical Footing Drain Detail Figure 4 Not to Scale Geotechnical Engineering Report May 17, 2019 Genesis Homes Renton, Renton, Washington RGI Project No. 2019-092 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING On May 2, 2019, RGI performed field explorations using a rubber tired backhoe. We explored subsurface soil conditions at the site by observing the excavation of 3 test pits to a maximum depth of 10 feet below existing grade. The test pits locations are shown on Figure 2. The test pits locations were approximately determined by measurements from existing property lines and paved roads. A geologist from our office conducted the field exploration and classified the soil conditions encountered, maintained a log of each test exploration, obtained representative soil samples, and observed pertinent site features. All soil samples were visually classified in accordance with the Unified Soil Classification System (USCS). Representative soil samples obtained from the explorations were placed in closed containers and taken to our laboratory for further examination and testing. As a part of the laboratory testing program, the soil samples were classified in our in house laboratory based on visual observation, texture, plasticity, and the limited laboratory testing described below. Moisture Content Determinations Moisture content determinations were performed in accordance with ASTM D2216-10 Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass (ASTM D2216) on representative samples obtained from the exploration in order to aid in identification and correlation of soil types. The moisture content of typical sample was measured and is reported on the test pits logs. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses was determined using D6913-04(2009) Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM D6913) on two of the samples. Project Name:Genesis Homes Renton Project Number:2019-092 Client:Genesis Homes, LLC Test Pit No.: TP-1 Date(s) Excavated:05/02/19 Excavation Method:Excavation Excavator Type:Mini-Excavator Groundwater Level and Date Measured Not encountered Test Pit Backfill:Native Soil Logged By LC Bucket Size: Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1501 Kirkland Avenue Northeast, Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:10 feet bgs Approximate Surface Elevation n/a Compaction Method n/a USCS SymbolGrass SM SP-SM REMARKS AND OTHER TESTS 7% Moisture 14% Moisture 9% Moisture 11% MoistureGraphic LogMATERIAL DESCRIPTION Grass Reddish brown, silty SAND with trace gravel, medium dense, moist Gray, SAND with silt, dense, moist Test pit excavated to 10 feet bgs No groundwater encounteredDepth (feet)0 5 10 15 Sample NumberTP1-1 TP1-5 TP1-7.5 TP1-10Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Genesis Homes Renton Project Number:2019-092 Client:Genesis Homes, LLC Test Pit No.: TP-2/IT-1 Date(s) Excavated:05/02/19 Excavation Method:Excavation Excavator Type:Mini-Excavator Groundwater Level and Date Measured Not encountered Test Pit Backfill:Native Soil Logged By LC Bucket Size: Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1501 Kirkland Avenue Northeast, Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:11 feet bgs Approximate Surface Elevation n/a Compaction Method n/a USCS SymbolGrass SM SP-SM REMARKS AND OTHER TESTS 4% Moisture 8% Moisture 14% MoistureGraphic LogMATERIAL DESCRIPTION Grass Reddish brown, silty SAND with trace gravel, medium dense, moist Gray, SAND with some silt and trace gravel, medium dense to dense, moist Infiltration test, IT-1, performed 6 feet bgs Test pit excavated to 11 feet bgs No groundwater encounteredDepth (feet)0 5 10 15 Sample NumberTP2-1 TP2-3 TP2-6Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Genesis Homes Renton Project Number:2019-092 Client:Genesis Homes, LLC Test Pit No.: TP-3 Date(s) Excavated:05/02/19 Excavation Method:Excavation Excavator Type:Mini-Excavator Groundwater Level and Date Measured Not encountered Test Pit Backfill:Native Soil Logged By LC Bucket Size: Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1501 Kirkland Avenue Northeast, Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:11 feet bgs Approximate Surface Elevation n/a Compaction Method n/a USCS SymbolGrass SM SM REMARKS AND OTHER TESTS 6% Moisture 10% MoistureGraphic LogMATERIAL DESCRIPTION Grass Reddish brown, silty SAND with trace gravel, medium dense, moist Gray, silty SAND with trace gravel, medium dense, moist Test pit excavated to 11 feet bgs No groundwater encounteredDepth (feet)0 5 10 15 Sample NumberTP3-1 TP3-5Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Genesis Homes Renton Project Number:2019-092 Client:Genesis Homes, LLC Key to Logs USCS SymbolREMARKS AND OTHER TESTSGraphic LogMATERIAL DESCRIPTIONDepth (feet)Sample NumberSample TypeElevation (feet)1 2 3 4 5 6 7 8 COLUMN DESCRIPTIONS 1 Elevation (feet): Elevation (MSL, feet). 2 Depth (feet): Depth in feet below the ground surface. 3 Sample Type: Type of soil sample collected at the depth interval shown. 4 Sample Number: Sample identification number. 5 USCS Symbol: USCS symbol of the subsurface material. 6 Graphic Log: Graphic depiction of the subsurface material encountered. 7 MATERIAL DESCRIPTION: Description of material encountered. May include consistency, moisture, color, and other descriptive text. 8 REMARKS AND OTHER TESTS: Comments and observations regarding drilling or sampling made by driller or field personnel. FIELD AND LABORATORY TEST ABBREVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent PI: Plasticity Index, percent SA: Sieve analysis (percent passing No. 200 Sieve) UC: Unconfined compressive strength test, Qu, in ksf WA: Wash sieve (percent passing No. 200 Sieve) MATERIAL GRAPHIC SYMBOLS Grass and/or topsoil Silty SAND (SM) Poorly graded SAND with Silt (SP-SM) TYPICAL SAMPLER GRAPHIC SYMBOLS Auger sampler Bulk Sample 3-inch-OD California w/ brass rings CME Sampler Continuous Grab Sample 2.5-inch-OD Modified California w/ brass liners Pitcher Sample 2-inch-OD unlined split spoon (SPT) Shelby Tube (Thin-walled, fixed head) OTHER GRAPHIC SYMBOLS Water level (at time of drilling, ATD) Water level (after waiting) Minor change in material properties within a stratum Inferred/gradational contact between strata ?Queried contact between strata GENERAL NOTES 1: Soil classifications are based on the Unified Soil Classification System. Descriptions and stratum lines are interpretive, and actual lithologic changes may be gradual. Field descriptions may have been modified to reflect results of lab tests. 2: Descriptions on these logs apply only at the specific boring locations and at the time the borings were advanced. They are not warranted to be representative of subsurface conditions at other locations or times. Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415‐0551 FAX: (425) 415‐0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Genesis Homes Renton SAMPLE ID/TYPE TP3‐5 PROJECT NO.2019‐092 SAMPLE DEPTH 5 feet TECH/TEST DATE LW/CM 5/8/2019 DATE RECEIVED 5/2/2019 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)548.2 Weight Of Sample (gm)511.0 Wt Dry Soil & Tare (gm) (w2)511.0 Tare Weight (gm) 133.2 Weight of Tare (gm) (w3)133.2 (W6) Total Dry Weight (gm) 377.8 Weight of Water (gm) (w4=w1‐w2) 37.2 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2‐w3) 377.8 Cumulative Moisture Content (%) (w4/w5)*100 10 Wt Ret (Wt‐Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100‐%ret) % COBBLES 0.0 12.0"133.2 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"133.2 0.00 0.00 100.00 coarse gravel % F GRAVEL 8.2 2.5" coarse gravel % C SAND 5.3 2.0" coarse gravel % M SAND 35.6 1.5"133.2 0.00 0.00 100.00 coarse gravel % F SAND 36.4 1.0" coarse gravel % FINES 14.5 0.75"133.2 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"147.3 14.10 3.73 96.27 fine gravel D10 (mm)#4 164.2 31.00 8.21 91.79 coarse sand D30 (mm)#10 184.1 50.90 13.47 86.53 medium sand D60 (mm)#20 medium sand Cu #40 318.7 185.50 49.10 50.90 fine sand Cc #60 fine sand #100 432.4 299.20 79.20 20.80 fine sand #200 456.4 323.20 85.55 14.45 fines PAN 511.0 377.80 100.00 0.00 silt/clay 322 188.8 49.973531 50.026469 DESCRIPTION Silty SAND with trace gravel USCS SM Prepared For: Reviewed By: KW Genesis Homes, LLC 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3" 2" 1" .75" .375" #4 #10 #20 #40 #60 #100 #200 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415‐0551 FAX: (425) 415‐0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Genesis Homes Renton SAMPLE ID/TYPE TP2‐6 PROJECT NO.2019‐092 SAMPLE DEPTH 6 feet TECH/TEST DATE LW/CM 5/8/2019 DATE RECEIVED 5/2/2019 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)583.5 Weight Of Sample (gm)528.9 Wt Dry Soil & Tare (gm) (w2)528.9 Tare Weight (gm) 125.2 Weight of Tare (gm) (w3)125.2 (W6) Total Dry Weight (gm) 403.7 Weight of Water (gm) (w4=w1‐w2) 54.6 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2‐w3) 403.7 Cumulative Moisture Content (%) (w4/w5)*100 14 Wt Ret (Wt‐Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100‐%ret) % COBBLES 0.0 12.0"125.2 0.00 0.00 100.00 cobbles % C GRAVEL 2.9 3.0"125.2 0.00 0.00 100.00 coarse gravel % F GRAVEL 8.3 2.5" coarse gravel % C SAND 8.0 2.0" coarse gravel % M SAND 33.5 1.5"125.2 0.00 0.00 100.00 coarse gravel % F SAND 42.3 1.0" coarse gravel % FINES 5.1 0.75"137.0 11.80 2.92 97.08 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"150.4 25.20 6.24 93.76 fine gravel D10 (mm)0.18 #4 170.5 45.30 11.22 88.78 coarse sand D30 (mm)0.28 #10 202.7 77.50 19.20 80.80 medium sand D60 (mm)0.77 #20 medium sand Cu 4.3 #40 337.8 212.60 52.66 47.34 fine sand Cc 0.6 #60 fine sand #100 495.9 370.70 91.83 8.17 fine sand #200 508.5 383.30 94.95 5.05 fines PAN 528.9 403.70 100.00 0.00 silt/clay 322 196.8 48.749071 51.2509289 DESCRIPTION Medium to fine SAND with some silt and trace gravel USCS SP‐SM Prepared For: Reviewed By: KW Genesis Homes, LLC 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3" 2" 1".75" .375" #4 #10 #20 #40 #60 #100 #200