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REVIEWED PLN Geotechnical_Report+4.20.2022mom RILEY GEOTECHNICAL ENGINEERING REPORT PREPARED BY: THE RILEY GROUP, INC. 17522 BOTHELL WAY NORTHEAST BOTHELL, WASHINGTON 98011 PREPARED FOR: Liu BROTHERS LLC c/o Lobsang Dargey — Anandacom 1641 EVERGREEN POINT ROAD MEDINA, WASHINGTON 98039 RGI PROJECT No. 2021-847-2 TERRACE PLACE EDMONDS 23625 84TH AVENUE WEST EDMONDS, WASHINGTON 98026 APRIL 12, 2022 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 + Fox 425.415.0311 RECEIVED Apr 22 2022 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT ■ ------------ Reviewed by City of Edmonds ; Planning Division =-------------- www. riley-group. corn now 1 LM RBLEYGROUP April 12, 2022 Liu Brothers LLC 1641 Evergreen Point Road Medina, Washington 98039 c/o Lobsong Dargey — Anondacom Subject; Geotechnical Engineering Report Terrace Place Edmonds 23625 84th Avenue West Edmonds, Washington 98026 RGI Project No. 2021-847-2 Dear Mr. Dargey: As requested, The Riley Group, Inc. (RGI) has prepared this Geotechnical Engineering Report (GER) for the above -referenced site. Our services were completed in accordance with our proposal 2021-847-PRP1 dated December 14, 2021 and authorized by you on December 17, 2021. The information in this report is based on our understanding of the proposed construction, and the soil and groundwater conditions encountered in the test pits completed by RGI at the site on March 18, 2022. RGI recommends the project plans and specifications be submitted for a general review so that RGI may confirm that the recommendations in this GER are interpreted and implemented properly in the construction documents. RGI also recommends that a representative of our firm be present on site during portions of the project construction to confirm that the soil and groundwater conditions are consistent with those that form the basis for the engineering recommendations in this GER. If you have any questions or require additional information, please contact us. Respectfully submitted, THE RILEY GROUP, INC. / of vvash� i rp f 1U) N Ql `��joyl �� .p 35013 0 ,it �CISTE�C )NAL.V" C,C I ERIC L. WOODS I Eric L. Woods, LG Project Geologist Ricky R. Wang, PhD, PE Principal Engineer Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 4 Fox 425.415.0311 r i I'll'. rlley-group, Vain Geotechnical Engineering Report Terrace Ploce Edmonds, Edmonds, Washington April 12, 2022 RGI Project No. 2021-847-2 TABLE OF CONTENTS 1.0 INTRODUCTION.................................................................................................................................... 1 2.0 PROJECT DESCRIPTION......................................................................................................................... 1 3.0 FIELD EXPLORATION............................................................................................................................. 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........................................................................................................................................ 2 4.5 SEISMIC CONSIDERATIONS...........................................................................................................................3 4.6 GEOLOGIC HAZARD AREAS..........................................................................................................................4 5.0 DISCUSSION AND RECOMMENDATIONS............................................................................................. 4 5.1 GEOTECHNICAL CONSIDERATIONS .................................................................................................................4 5.1.1 Erosion and Sediment Control.....................................................................................................4 5.1.2 Stripping.......................................................................................................................................5 5.1.3 Excavations...................................................................................................................................5 5.2 SHORING AND UNDERPINNING RECOMMENDATIONS........................................................................................6 5.2.1 Underpinning...............................................................................................................................6 5.2.2 Soldier Piles..................................................................................................................................6 5.2.3 Lagging.........................................................................................................................................8 5.2.4 Tiebacks........................................................................................................................................8 5.2.5 Soil Nails.....................................................................................................................................10 5.2.6 Construction Monitoring............................................................................................................11 5.2.7 Survey Monitoring......................................................................................................................11 5.3 EARTHWORK...........................................................................................................................................12 5.3.1 Site Preparation.........................................................................................................................12 5.3.2 Structural Fill..............................................................................................................................12 5.3.3 Wet Weather Construction Considerations...............................................................................14 5.4 FOUNDATIONS........................................................................................................................................ 14 5.5 RETAINING WALLS...................................................................................................................................15 5.5.1 Permanent Basement Walls.......................................................................................................15 5.5.2 Retaining Wall Design................................................................................................................15 5.6 SLAB -ON -GRADE CONSTRUCTION............................................................................................................... 16 5.7 DRAINAGE..............................................................................................................................................16 5.7.1 Surface.......................................................................................................................................16 5.7.2 Subsurface..................................................................................................................................17 5.7.3 Infiltration..................................................................................................................................17 5.8 UTILITIES................................................................................................................................................17 6.0 ADDITIONAL SERVICES.......................................................................................................................17 7.0 LIMITATIONS.......................................................................................................................................17 1 ,- RILEYGROUP Geotechnical Engineering Report ii Terrace Place Edmonds, Edmonds, Washington April 12, 2022 RGI Project No. 2021-847-2 LIST OF FIGURES AND APPENDICES Figure1.....................................................................................................................Site Vicinity Map Figure 2............................................................................................... Geotechnical Exploration Plan Figure 3 ..........................................Soldier Pile Pressure Diagram Cantilevered or One Row Tieback Figure 4............................................................................................Tieback Adhesion/No Load Zone Figure 5..............................................................................................................Soil Nail Wall Section Figure 6..............................................................................................Basement Wall Drainage Detail AppendixA................................................................................................................ Field Exploration 1 1 L- RILEYGROUP Geotechnical Engineering Report iii April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 Executive Summary This Executive Summary should be used in conjunction with the entire GER for design and/or construction purposes. It should be recognized that specific details were not included or fully developed in this section, and this 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 excavation of seven pits to depths up to 10.5 feet below ground surface (bgs). 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 site is underlain by up to 8.5 feet of loose to medium dense fill comprised of silty sand with some gravel over native deposits of loose to medium dense silty sand with some gravel over dense silty sand with varying amounts of gravel glacial till. Groundwater: Groundwater seepage was encountered at three test pit locations at depths of 1.5 to 8 feet during our subsurface explorations. Underpinning: Underpinning may be needed for the building to the southeast of the site. Temporary Shoring: The shoring system should consist of soldier piles with wood lagging and tieback anchors or soil nails with vertical elements as necessary for stability or underpinning of the adjacent buildings. Foundations: Foundations for the building should be supported on conventional foundations bearing on very dense native soil. Slab -on -grade: Slab -on -grade floors for the proposed building should be supported on competent native soil or structural fill. mom 1 L- RILEYGROUP Geotechnical Engineering Report 1 April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 1.0 Introduction This Geotechnical Engineering Report (GER) presents the results of the geotechnical engineering services provided for the proposed Terrace Place Edmonds in Edmonds, Washington. The purpose of this GER is to explore subsurface conditions and provide geotechnical recommendations for a multi -story apartment building with one level of underground parking. 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 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 23625 84th Avenue West in Seattle, Washington. The approximate location of the site is shown on Figure 1. The site includes a tax parcel with a total area of about 1.8 acres in size (Snohomish Tax Parcel Number 00451900100900). RGI understands that the project will include a 260- unit apartment building with 7-story above ground surface and one -level below grade parking. RGI's understanding of the project is based on a site plan prepared by Charles Morgan & Associates dated December 13, 2021. 3.0 Field Exploration 3.1 FIELD EXPLORATION On March 18, 2022, RGI observed the excavation of seven test pits. The approximate exploration locations are shown on Figure 2. Field logs of each exploration were prepared by the geologist who 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 pit logs included in Appendix A represent an interpretation of the field logs and include modifications based on laboratory observation and analysis of the samples. 1 L- RILEYGROUP Geotechnical Engineering Report 2 Terrace Place Edmonds, Edmonds, Washington April1Z 2022 RGI Project No. 2021-847-2 3.2 LABORATORY TESTING During the field investigation, a representative portion of each recovered sample was sealed in containers and transported to our laboratory for further visual and laboratory examination. Samples retrieved from the pits 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 entire project site is an irregular -shaped tax parcel of land with a total area of about 1.8 acres. It is bound to the north by 236th Street Southwest, to the west by 84th Avenue West, to the south by developed properties and 238th Street Southwest, and to the east by commercial building. The site is a vacant lot. The site is relatively flat with an overall elevation difference of about 5 feet. The site contains several large soil stockpiles. The site is vegetated with grass and blackberries. 4.2 GEOLOGY Review of the Geologic Map of the Edmonds East and part of the Edmonds West Quadrangles, Washington by James P. Minard (1983) indicates that the soil in the project vicinity is mapped as Till (Map Unit Qvt) which is a compact mixture of clay, silt, sand, and gravel deposited by glacial ice. These descriptions are generally similar to the findings in our field explorations. 4.3 SOILS The site is underlain by up to 8.5 feet of loose to medium dense fill comprised of silty sand with some gravel over native deposits of loose to medium dense silty sand with some gravel over dense silty sand with varying amounts of gravel glacial till. More detailed descriptions of the subsurface conditions encountered are presented in the explorations included in Appendix A. 4.4 GROUNDWATER Groundwater seepage was encountered at three test pit locations at depths of 1.5 to 8 feet during our subsurface explorations. 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 1 �- RILEYGROUP Geotechnical Engineering Report 3 April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 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. Given the depth of groundwater level and proposed depth of excavation, the groundwater is likely to be encountered during the excavation. The amount of seepage should be light and RGI does not expect that it will have a major impact to the proposed development if the construction occurs during the dry season. 4.5 SEISMIC CONSIDERATIONS Based on ASCE 7-16 (To be used as 2018 IBC), RGI recommends the following seismic parameters provided in Table 1 be used for design. Table 1 IBC Parameter Site Soil Class' Site Latitude 2018 Value C2 47.784459 Site Longitude-122.345643 Short Period Spectral Response Acceleration, Ss (g) 1.277 1-Second Period Spectral Response Acceleration, S, (g) 0.448 Adjusted Short Period Spectral Response Acceleration, SMs (g) 1.533 Adjusted 1-Sec Period Spectral Response Acceleration, Sm, (g) 0.672 Numeric seismic design value at 0.2 second; SDS(g) 1.022 Numeric seismic design value at 1.0 second; SD1(9) 0.448 1. Note: In general accordance with Chapter 20 of ASCE 7-16. 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 7-16 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 excavations extended to a maximum depth of 10.5 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. 3. Note: In accordance with ASCE 11.4.8, a ground motion hazard analysis is not required for the following cases: • Structures on Site Class E sites with Ss greater than or equal to 1.0, provided the site coefficient Fa is taken as equal to that of Site Class C. • Structures on Site Class D sites with S, greater than or equal to 0.2, provided that the value of the seismic response coefficient Cs is determined by Eq. 12.8-2 for values of T <_ 1.5Ts and taken as equal to 1.5 times the value computed in accordance with either Eq. 12.8-3 for TL >_ T > 1.5T, or Eq. 12.8-4 for T > TL. • Structures on Site Class E sites with S, greater than or equal to 0.2, provided that T is less than or equal to Ts and the equivalent static force procedure is used for design. The above exceptions do not apply to seismically isolated structures, structures with damping systems or structures designed using the response history procedures of Chapter 16. 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. mom 1 L- RILEYGROUP Geotechnical Engineering Report 4 April 1Z 2022 Terrace Ploce Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 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. RGI reviewed the native soil condition for potential of liquefaction. The native soil is very dense glacial till which is considered not subject to soil liquefaction during a seismic event. 4.6 GEOLOGIC HAZARD AREAS Regulated geologically hazardous areas include erosion, landslide, earthquake, or other geological hazards. Based on the conditions observed on the site, 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. Underpinning may be needed for the building to the southeast of the site. Shoring will be needed along the perimeters of excavation. Foundations for the proposed structure can be supported on conventional spread footings bearing on the dense native soil. Slab -on -grade can be similarly supported on native soil. 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. 5.1.1 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): Y 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 Establishing a quarry spall construction entrance Installing siltation control fencing or anchored straw or coir wattles on the downhill side of work areas 1 L- RILEYGROUF Geotechnical Engineering Report 5 Terrace Place Edmonds, Edmonds, Washington April1Z 2022 RGI Project No. 2021-847-2 ➢ 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 ➢ 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. 5.1.2 STRIPPING Following removal of the existing pavement surface, the excavation for the lower levels and shoring installation can be completed. 5.1.3 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consisted of loose to medium dense silty sand with gravel over medium dense to very dense silty sand with varying gravel glacial till. 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 1-1/21-1:1V (Horizontal:Vertical) in fill or upper loose soil and 3/41-1:1V in very dense native soil. 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 5 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. mom 1 L- RILEYGROUP Geotechnical Engineering Report 6 April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 ➢ 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 SHORING AND UNDERPINNING RECOMMENDATIONS RGI expects that an excavation of up to 15 feet will be needed below the existing grade at the site to accommodate the proposed basement. The bottom of the excavation will be in very dense silty sand with gravel. Our geotechnical comments and recommendations concerning site excavations are presented below. 5.2.1 UNDERPINNING If the excavation is close the property line, underpinning may be needed below the existing building to the southeast of the site. Underpinning will provide vertical support for the building and eliminate lateral stresses that the foundations would impose on shoring and new lower level walls. RGI recommends using underpinning piles, which consist of steel beams installed beneath the footing in drilled shafts. The typical construction procedure for underpinning piles is to drill a shaft below the footing, install a steel beam, and align it vertically. The shaft annulus is then backfilled with structural concrete below the proposed excavation level and lean mix concrete above the proposed excavation level. The underpinning piles should be steel -wedged and shotcreted to ensure full contact with the bottom of the existing footing. Underpinning piles should extend a minimum depth of 10 feet below the proposed bottom of excavation level. At this depth, piles will be supported on dense to very dense native soil. The piles can be designed with a bearing capacity of 10 kips per square foot. The shaft resistance between structural concrete and native soils can be designed using 1,500 pounds per square foot (psf) in the undisturbed native soil. 5.2.2 SOLDIER PILES In our opinion, cantilevered soldier piles can be used for shoring the proposed excavation depth at the site. As an option, tieback design and installation recommendation is also provided. The following geotechnical comments and recommendations are provided concerning soldier piles. mom 1 L- RILEYGROUP Geotechnical Engineering Report 7 Terrace Ploce Edmonds, Edmonds, Washington April 12, 2022 RGI Project No. 2021-847-2 Soldier Pile Embedment All soldier piles must have sufficient embedment below the final excavation level to provide adequate kick -out resistance to horizontal loads, as calculated by the design engineer. For cantilevered soldier piles, RGI recommends the embedment depth not be less than the exposed wall height or a minimum of 10 feet below the excavation base directly in front of each pile, whichever is more. Excavation Conditions Our subsurface explorations revealed that the site is underlain by medium dense to very dense silty sand with gravel. These soils can likely be drilled with a conventional auger, but the dense soil will undoubtedly yield slow excavation rates. Although none of our explorations encountered cobbles or previous construction obstruction, it should be realized that such obstructions could exist at random locations within these deposits. Applied Loads All soldier piles at the subject site should be designed to resist the various lateral loads applied to them. For a temporary shoring wall, RGI expects that these lateral loads will consist of active or at -rest pressures, slope surcharge, and possibly traffic surcharge, depending on the specific wall location. For a shoring wall that has adequate drainage, RGI does not expect that hydrostatic pressures will need to be considered. Our recommended design pressures, tieback adhesion and no load zone are presented graphically on Figure 3 and are discussed in the following paragraphs. Y Active Earth Pressures: Cantilever walls and tied -back walls that have only one row of tiebacks can be designed using active earth pressures shown on Figure 3. Traffic Surcharge Pressures: Lateral earth pressures acting on the soldier piles should be increased to account for traffic, construction equipment, material stockpiles, or other temporary loads located within a horizontal distance equal to half the wall height. The streets located adjacent to the northern and eastern site boundary will result in a traffic surcharge. For light to moderately heavy vehicles, this traffic surcharge can be modeled as a uniform lateral pressure of 75 psf acting over the upper 8 feet of wall; or heavy vehicles, such as concrete trucks, a value of 150 psf would be more appropriate. Hydrostatic Pressures: If groundwater is allowed to collect behind the shoring wall, a net hydrostatic pressure of 45 pounds per cubic foot (pcf) would act against the portion of wall above the foreslope level and below the saturation level. However, if adequate drainage is provided behind the shoring wall, we expect that hydrostatic pressures will not develop. Y Resisting Forces: Lateral resistance can be computed by using an appropriate passive earth pressure acting over the embedded portion of each soldier pile, 1 L- RILEYGROUF Geotechnical Engineering Report 8 April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 neglecting the upper 2 feet. This passive pressure should be applied over a lateral distance equal to the pile spacing or twice the pile diameter, whichever is less. For a level foreslope (measured perpendicular to the wall face), RGI recommends using a maximum allowable passive pressure modeled as an equivalent fluid density of 350 pcf, based on a safety factor of 1.5 or more. ➢ Pile Deflections: Lateral deflections for a soldier pile can be calculated from the horizontal modulus of subgrade reaction, which generally increases with depth. As a reasonable approximation, however, a uniform modulus of 350 pounds per cubic inch (pci) can be used. 5.2.3 LAGGING RGI recommends that lagging be installed between all adjacent soldier piles to reduce the potential for soil caving, backslope subsidence, and hazardous working conditions. Our geotechnical comments and recommendations about lagging are presented below. Lateral Materials and Pressures In our opinion, pressure -treated timbers can be utilized as lagging at the site. Due to soil arching effects, temporary lagging that spans 8 feet or less need be designed for only 50 percent of the lateral earth pressure previously recommended for soldier pile design. Permanent lagging, on the other hand, should be designed for 75 percent of this same lateral earth pressure. In both cases, these values assume that adequate drainage is provided behind the lagging, as discussed below. Lagging Backfill RGI recommends that any voids behind the lagging be backfilled with a material sufficiently pervious to allow groundwater flow and prevent a build-up of hydrostatic pressure. For this reason, permeable materials such as granular excavation spoils, clean sand, or pea gravel are suitable as backfill material, whereas silty soils, cement grout, controlled -density fill, or other less -permeable materials are not suitable. Drainage System RGI recommends that all lagging backfill material connect to a continuous horizontal drain located in front of the wall. This can be accomplished either by extending gravel under the lagging or by providing gaps between the lagging boards. If concrete or shotcrete walls are to be placed against wooden lagging, prefabricated vertical drainage strips (such as MiraDRAIN 6000) should be attached to each lagging bay. 5.2.4 TIEBACKS Tiebacks comments and recommendations are summarized below and are illustrated on the attached Figure 4. mom 1 L- RILEYGROUP Geotechnical Engineering Report 9 Terrace Ploce Edmonds, Edmonds, Washington April 12, 2022 RGI Project No. 2021-847-2 Conflicts and Easements Because tiebacks typically extend about 30 to 60 feet behind the excavation face, conflicts with underground utilities and adjacent structures often arise. The project structural engineer should carefully consider the locations of such obstructions when laying out all tiebacks. Furthermore, temporary easements will be required for any tiebacks that extend beyond the site's property boundaries, and it should be realized that the City of Seattle does not typically allow permanent tiebacks under their roadways and alleyways. Installation Methods All tiebacks should be installed in a manner that minimizes caving and associated ground subsidence. Typically, this involves excavation with a full-length casing or continuous flight auger, as well as pumping grout from the bottom of each tieback hole with a tremie. If desired, the shoring contractor can use secondary pressure -grouting techniques to reduce auger diameters and develop greater adhesion values. No -Load Zone The anchor portion of all tiebacks must be located a sufficient distance behind the retained excavation face in order to develop resistance within a stable soil mass. We specifically recommend that the anchorage be obtained behind a "no-load zone" defined by a plane set back from the wall face a horizontal distance equal to 25 percent of the wall height and projected upward at a 60-degree angle from the excavation base level. This configuration is shown on Figure 4. Anchor Length and Spacing The anchor portion of all tiebacks must have sufficient embedment below the backslope surface and behind the no-load zone to provide adequate pull-out resistance to lateral loads, as calculated by the design engineer. RGI recommends providing a minimum anchor depth of 10 feet and a minimum anchor length of 20 feet. To avoid interactions between adjacent tiebacks, RGI further recommends that a clear spacing of at least 5 feet be maintained along the anchor zones. Estimated Adhesion If properly grouted, RGI tentatively estimates that an allowable concrete/soil adhesion of 1,500 psf can be assumed for the anchor portion of a tieback located within the medium dense to dense silty sands. Secondary pressure -grouting techniques can often achieve adhesions two to three times greater than these values. In all cases, however, the actual design values will depend on the installation method and should be confirmed by load - testing all tiebacks in the field. 1 L- RILEYGROUP Geotechnical Engineering Report 10 Terrace Place Edmonds, Edmonds, Washington April1Z 2022 RGI Project No. 2021-847-2 Load Testing and Lock -Off Field testing of temporary tiebacks is necessary to confirm design assumptions, verify the integrity of individual tiebacks, and provide information regarding their short-term creep characteristics. Our recommended tests are described below. After testing, each tieback should be locked off at 100 percent of its design load. ➢ Performance Tests: A performance test load should be applied to selected production tiebacks at the site. RGI specifically recommends testing at least one tieback on each side of the excavation. The test load should equal 200 percent of the design capacity and be held for at least 60 minutes. ➢ Proof Tests: A proof test load should be applied to every production tieback at the site. The test load should equal 130 percent of the design capacity and be held for at least 10 minutes. 5.2.5 SOIL NAILS As an alternative to soldier pile wall, soil nail wall can be used. The concern of using soil nailing is soil standup time during the installation of the first row of soil nails. The first row of soil nails need to be carefully installed due to utilities in the right of way. Vertical nail elements may be needed for additional lateral support. Soil nailing stabilizes vertical excavations by reinforcing the soil mass with passive inclusions (soil nails). Soil nails typically consist of 3/4- to 1-3/8-inch-diameter steel bars that are centrally grouted in 6- to 8-inch-diameter augered holes. The nails are normally spaced at 4- to 6-foot centers. Following the installation of a row of nails, the excavation face is covered with a shotcrete facing that is reinforced with either welded wire mesh or rebar. The nails are then secured to the shotcrete wall with a steel plate and bolt assembly. A typical soil nail wall detail is shown on Figure 5. Once grout strengths are achieved, the excavation continues below the wall and the construction sequence is repeated until the bottom of the excavation is reached. Soil Nail Design Based on the soils encountered at the site, RGI recommends using the following soil parameters for soil nailing design: mom 1 L- RILEYGROUP Geotechnical Engineering Report 11 Terrace Place Edmonds, Edmonds, Washington April1Z 2022 RGI Project No. 2021-847-2 Table 2 Soil Nail Design Parameters Unit Weight Friction Shaft Soil Parameter (pcf) Angle Cohesion (psf) Resistance (psf) Medium dense to dense sand 125 34 200 1,500 Excavation and wall construction sequencing should not exceed a height of 6 feet. Care must be taken to prevent caving during initial excavation in loose surface soils. Temporary protection such as soil berms and flash coating should be considered. The shaft resistance assumes open hole tremie grouting. Soil nail verification tests should be performed to verify the soil resistance before construction. Conflicts and Easements Because soil nails typically extend about 20 to 30 feet behind the excavation face, conflicts with underground utilities and adjacent structures often arise. The project structural engineer or shoring designer should carefully consider the locations of such obstructions when laying out all tiebacks. Furthermore, temporary easements will be required for any nails that extend beyond the site's property boundaries. 5.2.6 CONSTRUCTION MONITORING Because shoring requires specialized installation and earthwork techniques to maintain stable conditions during and after construction, RGI strongly recommends that an RGI representative be retained to continuously monitor all construction activities. This would include observation and documentation of installation procedures, construction materials, and excavation conditions. 5.2.7 SURVEY MONITORING A monitoring program must be implemented to verify the performance of the shoring system and possible excavation effects on neighboring buildings. The first step in this program should consist of surveying building feature elevations and documenting the condition of the existing properties and adjacent buildings. This documentation should include a photographic record. Monitoring points should be set by a licensed surveyor on the adjacent streets and structures at a maximum of 25-foot intervals with a minimum of two on each side of the excavation. Monitoring of the shoring system should occur two times per week as the excavation proceeds and then once every two weeks once the excavation is completed. A registered land surveyor should be retained to establish the baseline data and obtain the bi-weekly readings. Monitoring data can be obtained by the project contractor. Monitoring should continue until the permanent new lower walls are adequately braced and should include surveying the vertical and horizontal alignment of the top of every other soldier pile. The mom 1 L- RILEYGROUP Geotechnical Engineering Report 12 April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 project's structural and geotechnical engineers should review the monitoring data weekly. 5.3 EARTHWORK After completion of the shoring and removal of the soils to subgrade elevation, the site earthwork is expected to consist of excavating foundations, installing under slab utilities and preparing the slab subgrade. 5.3.1 SITE PREPARATION 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. 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. 5.3.2 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 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 2 percent of the optimum moisture level as determined by American Society of Testing and Materials D1557-09 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (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 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 mom 1 L- RILEYGROUP Geotechnical Engineering Report 13 April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 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 conditioning prior to use as structural fill depending on the time of year and weather conditions at the time of excavation. 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 3 to be used as structural fill. Table 3 Structural Fill Gradation U.S. Sieve Size 4 inches No. 4 sieve No. 200 sieve *Based on minus 3/4 inch fraction. Percent Passing 100 22 to 100 0to5* 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 4. The soil's maximum density and optimum moisture should be determined by ASTM D1557. mom 1 L- RILEYGROUP Geotechnical Engineering Report 14 Terrace Place Edmonds, Edmonds, Washington April1Z 2022 RGI Project No. 2021-847-2 Table 4 Structural Fill Compaction ASTM D1557 Minimum Moisture Content Location Material Type Compaction Percentage Range Foundations On -site granular or approved 95 +2 -2 imported fill soils: Retaining Wall Backfill On -site granular or approved 92 +2 2 imported fill soils: Slab -on -grade On -site granular or approved 95 +2 -2 imported fill soils: General Fill (non- on -site soils or approved 90 +3 -2 structural areas) imported fill soils: Pavement — Subgrade On -site granular or approved 95 +2 - 2 and Base Course imported fill soils: 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. 5.3.3 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. 5.4 FOUNDATIONS Following site preparation and excavation, the proposed building foundation can be supported on conventional spread footings bearing on dense native soil. The parameters in Table 5 can be used for the foundation design. mom 1 L- RILEYGROUP Geotechnical Engineering Report 15 Terrace Place Edmonds, Edmonds, Washington April1Z 2022 RGI Project No. 2021-847-2 Table 5 Foundation Design Design Parameter Allowable Bearing Capacity — Dense Native Soil Value 5,000 psfl Friction Coefficient I 0.3 Passive pressure (equivalent fluid pressure) I 250 pcfz 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 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 5.3.2. The recommended base friction and passive resistance value includes a safety factor of about 1.5. 5.5 RETAINING WALLS RGI expects the below grade level basement walls will be formed directly against shoring. If retaining walls are needed outside of the building area, RGI recommends cast -in -place concrete walls be used. 5.5.1 PERMANENT BASEMENT WALLS The basement walls formed against cantilever soldier pile and tieback shoring should be designed for the earth pressures provided on Figure 3. Permanent basement walls formed against soil nail shoring should be designed for the values in Table 6 below. Permanent basement walls formed against shoring should be provided with drainage. A typical drainage system for walls formed against shoring is attached as Figure 6. 5.5.2 RETAINING WALL DESIGN With wall backfill placed and compacted as recommended or formed directly against the temporary soil nail wall, and drainage properly installed, RGI recommends using the values in the following table for design. mom 1 L- RILEYGROUP Geotechnical Engineering Report 16 Terrace Place Edmonds, Edmonds, Washington Table 6 Retaining Wall Design Design Parameter Allowable Bearing Capacity — Dense Native Soil Active Earth Pressure (unrestrained walls) April1Z 2022 RGI Project No. 2021-847-2 Value 5,000 psf 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 5.4. 5.6 SLAB -ON -GRADE CONSTRUCTION Once site preparation has been completed as described in Section 5.2, slab -on -grade construction can be supported on competent native soils. If loose soil is encountered, it should be removed and replaced with structural fill. Immediately below the floor slab, RGI recommend placing a 4-inch-thick capillary break layer of clean, free -draining sand or gravel that has less than 5 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-mil-thick plastic membrane should be placed on a 4-inch-thick layer of clean gravel. For the anticipated floor slab loading, RGI estimates post -construction floor settlements of 1/4- to 1/2-inch. For thickness design of the slab subjected to point loading from storage racks, RGI recommends using a subgrade modulus (Ks) of 150 pounds per square inch per inch of deflection. 5.7 DRAINAGE 5.7.1 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. mom 1 L- RILEYGROUP Geotechnical Engineering Report 17 Terrace Place Edmonds, Edmonds, Washington April1Z 2022 RGI Project No. 2021-847-2 5.7.2 SUBSURFACE RGI recommends installing retaining wall drains as shown on Figure 6. 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. 5.7.3 INFILTRATION RGI evaluated the feasibility of onsite infiltration. The native soil is dense to very glacial till which is not suitable for infiltration system. Therefore, RGI does not recommend an infiltration system be used. The roof runoff should be tightlined and discharged to public stormwater system. 5.8 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 Edmonds or Snohomish County specifications. At a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.3.2. 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 ASTM D1557. 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. If these services are desired, please let us know and we will prepare a proposal. 7.0 Limitations This GER is the property of RGI, Liu Brothers LLC, and their designated agents. Within the limits of the scope and budget, this GER was prepared in accordance with generally accepted geotechnical engineering practices in the area at the time this report was issued. This GER is intended for specific application to the Terrace Place Edmonds project at the southeast corner of 23625 84th Avenue West in Edmonds, Washington, and for the mom 1 L- RILEYGROUP Geotechnical Engineering Report 18 April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 exclusive use of Liu Brothers 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 our review of the referenced documents. 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. mom 1 L- RILEYGROUP �T— CLI LW 22 ST 6� QFsw J 'Esperanc LW 00" 'T z � � MNo AP k ba I 236 238THISF SW S 240THIT SW I/� 242MD ST SW 28TH,ST- r f� F\ Nk 205TT H S Tf� N 205TH ST N "NW405TH-S-T 90TH Sr N 200THiST _ ' $o '' ,j USGS, 2020, Edmonds East, Washington Approximate Scale: 1"=1000' 7.5-Minute Quadrangle 0 500 1000 2600 N Corporate Office Edmonds Terrace Development Figure 1 17522 Bothell Way Northeast RGI Project Number: Date Drawn: I LWpBothell, Washington 98011 2021-847-2 F Site Vicinity Map Phone: 425.415.0551 04/2022 FULEYGROUPFax: 425.415.0311 Address: 23625 84th Avenue West, Edmonds, Washington 98026 236TH ST SW I �I TP-1 f1-1F11 ■ 0 ■.11[7-['! Allm ti TP-7 I I I I I I I I {a = Test pit by RGI 03/18/22 Approximate Scale: 1"= 50' — — — = Property boundary 0 25 50 100 N Corporate Office Edmonds Terrace Development Figure 2 17522 Bothell Way Northeast MBothell, Washington 98011 RGI Project Number: Geotechnical Exploration Plan Date Drawn: 2021-847-2 04/2022 LEY Phone: 425.415.0551 Fax: 425.415.0311 Address: 23625 84th Avenue West, Edmonds, Washington 98026 Earth Pressure Design Parameters for Soldier Pile Cantilever Wall 2' T- Passive Earth Pressure = 350 pcf taken over 2 pile diameters Note: Value includes Reduction Factor of 1.5. R 50 pcf for 2H:1V Slope or 35 pcf for Level Ground Not to Scale 8' 75 psf (Traffic Surcharge where applicable) Corporate Office Edmonds Terrace Development Figure 3 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 RGI Project Number: 2021-847-2 Soldier Pile Pressure Diagram Date Drawn: 04/2022 ]LEY Fax: 425.415.0311 Address: 23625 84th Avenue West, Edmonds, Washington 98026 Tieback Soldier Pile/Lagging Shoring Wall Tieback Adhesion/No Load Zone Not to Scale Corporate Office Edmonds Terrace Development Figure 4 I 17522 Bothell Way Northeast MBothell, Washington 98011 Phone: 425.415.0551 RGI Project Number: 2021-847-2 Tieback Adhesion/No Load Zone Date Drawn: 04/2022 ILEY Fax: 425.415.0311 Address: 23625 84th Avenue West, Edmonds, Washington 98026 Welded Wire Mesh, Held 2-1/2" off Soil Face with Spaces. See Specifications for Requirements Mild Steel Plate, 8" x 8" x 1/2", with Oversized Hold (Bar Dia. + 1/4" Minimum) Titan Anchor Bar to Protrude at Least 12" from Soil Face Before Shotcreting. Length of Protrusion Included in Nail Lengths Spherical Seal Nut or Hex Nut with Beveled Washer Soil Nail Wall Section 24-Inch Wide Fabric Drain Strip (Miradrain 6000 or Equivalent) Spaced 6 Feet on Center. Extend Under Wall to Pea Gravel Layer. Waler Bars - 2 #4 Deformed Steel Bars, Extending Horizontally Between Adjacent Nails. Shotcrete Centralizer, to Hold Bar in Middle Third of Hole. �I I-- Shotcrete, Min. 4" Thick. Not to Scale Anchor Grout Corporate Office Edmonds Terrace Development Figure 5 17522 Bothell Way Northeast Bothell, Washington 98011 Phone:425.415.0551 RGI Project Number: 2021-847-2 Soil Nail Wall Section Date Drawn: 04/2022 ILEY Fax: 425.415.0311 Address: 23625 84th Avenue West, Edmonds, Washington 98026 d ad. Drain Grate Wood Lagging or Temporary Soil Nail Wall Concrete Facing Miradrain 6000 or Equivalent Slab -On -Grade Floor 4" PVC Collection Pipe Note: Drain Though Wall Should be Installed at Middle of Lagging, or at 10 foot intervals in the soil nail wall. Not to Scale Corporate Office Edmonds Terrace Development Figure 6 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 RGI Project Number: 2021-847-2 Basement Wall Drainage Detail Date Drawn: 04�2022 ]LEY Fax: 425.415.0311 Address: 23625 84th Avenue West, Edmonds, Washington 98026 Geotechnical Engineering Report April 12, 2022 Terrace Place Edmonds, Edmonds, Washington RGI Project No. 2021-847-2 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING On March 18, 2022, RGI performed field explorations using an excavator. We explored subsurface soil conditions at the site by observing the excavation of seven test pits to a maximum depth of 10.5 feet below existing grade. The test pit locations are shown on Figure 2. The test pit 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 pit 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. mom 1 L- RILEYGROUP Project Name: Edmonds Terrace Development Test Pit No.: TP-1 Project Number: 2021-847-2 Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 Date(s) Excavated: 3/18/2022 Logged By ELW Surface Conditions: Grass Excavation Method: Test Pit Bucket Size: N/A Total Depth of Excavation: 6 feet bgs Excavator Type: Mini Excavator Excavating Contractor: Kelly's Excavating Approximate N/A Surface Elevation Groundwater Level: Seepage at 1.5' Sampling Grab Method(s) Compaction Method Bucket Test Pit Backfill: Cuttings Location 23625 84th Avenue West, Edmonds, Washington n E O H O Z N T to —J U L O O_ U) Q (6 w 0 <n U) D cD MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 TPSL 6" topsoil Fill Brown silty SAND with some gravel, loose, moist SM Reddish brown silty SAND with some gravel, loose to medium dense, moist 1 IF32% Light groundwater seepage . moisture SM Gray mottled silty SAND with trace gravel, medium dense, moist to wet (Glacial Till) 19% moisture, 22% fines Becomes gray, dense, moist 15% moisture 5 Becomes very dense Test pit terminated at 6' 10 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Edmonds Terrace Development Test Pit No.: TP-2 Project Number: 2021-847-2 Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 Date(s) Excavated: 3/18/2022 Logged By ELW Surface Conditions: Grass Excavation Method: Test Pit Bucket Size: N/A Total Depth of Excavation: 6.5 feet bgs Excavator Type: Mini Excavator Excavating Contractor: Kelly's Excavating Approximate N/A Surface Elevation Groundwater Level: Not Encountered Sampling Grab Method(s) Compaction Method Bucket Test Pit Backfill: Cuttings Location 23625 84th Avenue West, Edmonds, Washington n E H Z T to _J O O N U L O O_ U) Q (6 w 0 <n U) co D cD MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 TPSL 4" topsoil SM Tan silty SAND with some gravel, loose to medium dense, moist sM Gray mottled silty SAND with some gravel, medium dense, moist (Glacial Till) 25% moisture Becomes gray, dense 5 Becomes very dense 14% moisture Test Pit terminated at 6.5' 10 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Edmonds Terrace Development Test Pit No.: TP-3 Project Number: 2021-847-2 Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 Date(s) Excavated: 3/18/2022 Logged By ELW Surface Conditions: Grass Excavation Method: Test Pit Bucket Size: N/A Total Depth of Excavation: 5.5 feet bgs Excavator Type: Mini Excavator Excavating Contractor: Kelly's Excavating Approximate N/A Surface Elevation Groundwater Level: Not Encountered Sampling Grab Method(s) Compaction Method Bucket Test Pit Backfill: Cuttings Location 23625 84th Avenue West, Edmonds, Washington n E O H O Z N T to _J U L O O_ co U) Q (6 w 0 <n U) D cD MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 TPSL 3" topsoil Fill Brown to gray silty SAND with some gravel, loose to medium dense, moist (Fill) Trace wood debris SM Gray mottled silty gravelly SAND, medium dense, moist (Glacial Till) Becomes gray, dense 14% moisture, 27% fines 5 Test Pit terminated at 5.5' 10 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Edmonds Terrace Development Test Pit No.: TP-4 Project Number: 2021-847-2 Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 Date(s) Excavated: 3/18/2022 Logged By ELW Surface Conditions: Blackberries Excavation Method: Test Pit Bucket Size: N/A Total Depth of Excavation: 6 feet bgs Excavator Type: Mini Excavator Excavating Contractor: Kelly's Excavating Approximate N/A Surface Elevation Groundwater Level: Seepage at 1.5' Sampling Grab Method(s) Compaction Method Bucket Test Pit Backfill: Cuttings Location 23625 84th Avenue West, Edmonds, Washington n E H Z T _J O O N to U L O O_ U) Q (6 w 0 <n U) co D cD MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 TPSL 8" topsoil sm Tan silty SAND with some gravel, medium dense, wet (Glacial Till) Light groundwater seepage 18% moisture Becomes moist to wet Becomes gray, dense, moist Becomes very dense 5 13% moisture Test Pit terminated at 6' 10 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Edmonds Terrace Development Test Pit No.: TP-5 Project Number: 2021-847-2 Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 Date(s) Excavated: 3/18/2022 Logged By ELW Surface Conditions: Grass Excavation Method: Test Pit Bucket Size: N/A Total Depth of Excavation: 5.5 feet bgs Excavator Type: Mini Excavator Excavating Contractor: Kelly's Excavating Approximate N/A Surface Elevation Groundwater Level: Not Encountered Sampling Grab Method(s) Compaction Method Bucket Test Pit Backfill: Cuttings Location 23625 84th Avenue West, Edmonds, Washington n E H Z T _J O O N to U L O O_ U) Q (6 w 0 <n U) co D cD MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 TPSL „ 12" topsoil sm Tan silty SAND with some gravel, loose to medium dense, moist to wet Becomes wet sm Gray mottled silty SAND with some gravel, medium dense, moist (Glacial Till) 17% moisture Becomes gray, dense s Becomes very dense 14% moisture Test Pit terminated at 5.5' 10 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Edmonds Terrace Development Test Pit No.: TP-6 Project Number: 2021-847-2 Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 Date(s) Excavated: 3/18/2022 Logged By ELW Surface Conditions: Grass, Blackberries Excavation Method: Test Pit Bucket Size: N/A Total Depth of Excavation: 10.5 feet bgs Excavator Type: Mini Excavator Excavating Contractor: Kelly's Excavating Approximate N/A Surface Elevation Groundwater Level: Seepage at 8' Sampling Grab Method(s) Compaction Method Bucket Test Pit Backfill: Cuttings Location 23625 84th Avenue West, Edmonds, Washington n E H Z T _J O O N to U L O O_ U) Q (6 w 0 <n U) co D cD MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 Fill Dark brown silty SAND with gravel and organics, loose, moist (Fill) Contains wood, concrete, plastic, metal debris 5 Contains bricks 42% moisture Contains wood and concrete debris Becomes wet Light groundwater seepage sm Tan mottled silty SAND with some gravel, medium dense, moist (Glacial Till) 19% moisture Becomes gray, dense 10 16% moisture Test Pit terminated at 10.5' The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Edmonds Terrace Development Test Pit No.: TP-7 Project Number: 2021-847-2 Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 Date(s) Excavated: 3/18/2022 Logged By ELW Surface Conditions: Blackberries Excavation Method: Test Pit Bucket Size: N/A Total Depth of Excavation: 8 feet bgs Excavator Type: Mini Excavator Excavating Contractor: Kelly's Excavating Approximate N/A Surface Elevation Groundwater Level: Not Encountered Sampling Grab Method(s) Compaction Method Bucket Test Pit Backfill: Cuttings Location 23625 84th Avenue West, Edmonds, Washington n E H Z T to _J O O N U L O O_ U) Q (6 w 0 <n U) D (D MATERIAL DESCRIPTION REMARKS AND OTHER TESTS 0 TPSL 8" topsoil Fill Brown silty SAND with some gravel, loose, moist (Fill) Contains brick debris Some organics Contains large boulder Becomes moist to wet 5 sm Tan mottled silty SAND with some gravel, medium dense, moist (Glacial Till) 16% moisture Becomes gray, dense Test Pit terminated at 8' 10 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name: Edmonds Terrace Development Key to Logs Project Number: 2021-847-2 I- Client: Liu Brothers LLC RILEYGROUP Sheet 1 of 1 _ O - Q H O E Z N T W _J U > a at E m E a1 U W n w o U)i W D C� MATERIAL DESCRIPTION I REMARKS AND OTHER TESTS COLUMN DESCRIPTIONS 1 Elevation (feet): Elevation (MSL, feet). 2 Depth (feet): Depth in feet below the ground surface. LIJ Sample Type: Type of soil sample collected at the depth interval shown. ® Sample Number: Sample identification number. FIELD AND LABORATORY TEST ABBREVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent TYPICAL SAMPLER GRAPHIC SYMBOLS Auger sampler CME Sampler Bulk Sample Grab Sample 3-inch-OD California w/ 2.5-inch-OD Modified brass rings California w/ brass liners GENERAL NOTES 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. ® REMARKS AND OTHER TESTS: Comments and observations regarding drilling or sampling made by driller or field personnel. 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) Silty SAND (SM) Topsoil 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 v stratum Inferred/gradational contact between strata — ? — Queried contact between strata 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. 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 II GRAIN SIZE ANALYSIS II ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Edmonds Terrace Development PROJECT NO. 2021-847-2 TECH/TEST DATE CM 3/28/20 WATER CONTENT (Delivered Moisture) Wt Wet Soil & Tare (gm) (w1) 403.4 Wt Dry Soil & Tare (gm) (w2) 340.6 Weight of Tare (gm) (w3) 15.7 Weight of Water (gm) (w4=w1-w2) 62.8 Weight of Dry Soil (gm) (w5=w2-w3) 324.9 Moisture Content (%) (w4/w5)*100 19 % COBBLES % C GRAVEL % F GRAVEL % C SAND % M SAND % F SAND % FINES % TOTAL D10 (mm) D30 (mm) D60 (mm) Cu Cc 0.0 12.0' 3.0' 2.5' 2.0' 1.5' 1.0' 0.75' 0.50' 0.375' #4 #1C #2C #4C #6C 0.0 11.5 13.2 25.5 27.8 21.9 100.0 P A S S I N G #10C #20C PAN SAMPLE ID/TYPE TP-1 SAMPLE DEPTH 2.5feet DATE RECEIVED 3/18/2022 tal Weight Of Sample Used For Sieve Corrected For Hygroscopic Mc Weight Of Sample (gm) 340.6 Tare Weight (gm) 15.7 (W6) Total Dry Weight (gm) 324.9 SIEVE ANALYSIS Cumulative Wt Ret (Wt-Tare) (%Retained) % PASS +Tare 1(wt ret/w6)*1001 (100-%ret) 15.7 0.00 0.00 100.00 15.7 0.00 0.00 100.00 15.7 0.00 0.00 100.00 15.7 0.00 0.00 100.00 34.0 18.30 5.63 94.37 53.1 37.40 11.51 88.49 96.0 80.30 24.72 75.28 178.9 163.20 50.23 49.77 250.3 234.60 72.21 27.79 269.3 253.60 78.05 21.95 340.6 324.90 100.00 0.00 12" 3" 2" 1".75 .375" #4 #10 #20 #40 #60 #100 #200 100 90 80 70 60 50 40 30 20 10 0 1000 100 10 1 Grain size in millimeters DESCRIPTION Silty SAND with trace gravel USCS SM Prepared For: Liu Brothers LLC Reviewed By: ELW -obbles -oarse gravel -oarse gravel -oarse gravel -oarse gravel -oarse gravel fine gravel fine gravel fine gravel -oarse sand -nedium sand -nedium sand fine sand fine sand fine sand fines silt/clay 0.1 0.01 0.001 mom '- RILEYGROUP THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425)415-0311 II GRAIN SIZE ANALYSIS II ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Edmonds Terrace Development PROJECT NO. 2021-847-2 TECH/TEST DATE CM 3/28/20 WATER CONTENT (Delivered Moisture) Wt Wet Soil & Tare (gm) (w1) 499.5 Wt Dry Soil & Tare (gm) (w2) 441.6 Weight of Tare (gm) (w3) 15.7 Weight of Water (gm) (w4=w1-w2) 57.9 Weight of Dry Soil (gm) (w5=w2-w3) 425.9 Moisture Content (%) (w4/w5)*100 14 % COBBLES % C GRAVEL % F GRAVEL % C SAND % M SAND %FSAND % FINES % TOTAL D10 (mm) D30 (mm) D60 (mm) Cu Cc 0.0 12.0' 3.0' 2.5' 2.0' 1.5' 1.0' 0.75' 0.50' 0.375' #4 #1C #2C #4C #6C 30.0 2.6 4.2 15.1 21.2 26.9 100.0 P A S S I N G #10C #20C PAN SAMPLE ID/TYPE TP-3 SAMPLE DEPTH 4feet DATE RECEIVED 3/18/2022 tal Weight Of Sample Used For Sieve Corrected For Hygroscopic Mc Weight Of Sample (gm) 441.6 Tare Weight (gm) 15.7 (W6) Total Dry Weight (gm) 425.9 SIEVE ANALYSIS Cumulative Wt Ret (Wt-Tare) (%Retained) % PASS +Tare 1(wt ret/w6)*1001 (100-%ret) 15.7 0.00 0.00 100.00 15.7 0.00 0.00 100.00 122.3 122.30 28.72 71.28 143.6 127.90 30.03 69.97 143.6 127.90 30.03 69.97 154.6 138.90 32.61 67.39 172.7 157.00 36.86 63.14 236.9 221.20 51.94 48.06 300.1 284.40 66.78 33.22 327.1 311.40 73.12 26.88 441.6 425.90 100.00 0.00 12" 3" 2" 1".75 .375" #4 #10 #20 #40 #60 #100 #200 100 90 80 70 60 50 40 30 20 10 0 1000 100 10 1 Grain size in millimeters DESCRIPTION Silty gravelly SAND USCS SM Prepared For: Liu Brothers LLC Reviewed By: ELW -obbles -oarse gravel -oarse gravel -oarse gravel -oarse gravel -oarse gravel fine gravel fine gravel fine gravel -oarse sand -nedium sand -nedium sand fine sand fine sand fine sand fines silt/clay 0.1 0.01 0.001 mom '- RILEYGROUP