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HomeMy WebLinkAboutEx05_Geotechnical_Engineering_Design_Study Geotechnical Engineering Design Study Pan Abode Redevelopment Site Renton, Washington Prepared for Port Quendall Company May 20, 2021 19442-00 EXHIBIT 5 RECEIVED Clark Close 05/11/2023 PLANNING DIVISION DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 19442-00 May 20, 2021 Contents INTRODUCTION 1 SITE AND PROJECT DESCRIPTION 1 GENERALIZED SUBSURFACE CONDITIONS 2 Site Soils 3 Groundwater 3 SEISMIC DESIGN CONSIDERATIONS 3 Seismic Setting 3 Seismically Induced Geotechnical Hazards 4 Surface Fault Rupture 4 Soil Liquefaction 4 Lateral Spreading 5 Seismic Design Parameters 5 GEOTECHNICAL CONCLUSIONS AND RECOMMENDATIONS 6 General Considerations 7 Site Preparation and Grading 7 Augercast Pile Foundations 9 Vertical AC Pile Capacity (Compressive and Uplift) 9 Pile Downdrag Loads 10 Lateral AC Pile Loads 11 Pile Group Effects 11 Pile Cap and Grade Beam Passive Resistance 12 Pile Settlement 12 AC Pile Installation Considerations 13 Ground Improvement (GI) 14 General GI Design Criteria 14 GI Design Methodologies and Quality Control 15 GI Building Subgrade Preparation 16 Shallow Foundations 17 Concrete Slab-on-Grade Floors 18 Building Drainage Considerations 18 Asphalt Pavement Design and Subgrade Preparation 19 Pavement Subgrade Preparation 20 Stormwater Infiltration Considerations 20 Structural Fill 20 Use of On-Site Soil as Structural Fill 21 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 ii | Contents 19442-00 May 20, 2021 Imported Structural Fill 21 Temporary Open Cuts 22 RECOMMENDED ADDITIONAL GEOTECHNICAL SERVICES 22 Post-Report Design Services 22 Construction Observation Services 23 TABLES Table 1 – Building Code Seismic Design Parameters Error! Bookmark not defined. Table 2 – Vertical AC Pile Capacities (Compressive and Uplift) 10 Table 3 – LPILE Soil Parameters 11 Table 4 – LPILE Group Reduction Factors (P-Multipliers) 12 Table 5 – Typical Asphalt Pavement Design Sections 19 FIGURES 1 Vicinity Map 2 Site and Exploration Plan APPENDIX A Field Exploration Methods and Analysis APPENDIX B Soil Laboratory Testing APPENDIX C Historical Explorations DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 19442-00 May 20, 2021 Geotechnical Engineering Design Study Pan Abode Redevelopment Site Renton, Washington INTRODUCTION This report presents the results of our subsurface explorations and geotechnical engineering design study for the proposed Pan Abode Redevelopment Site in Renton, Washington. Our scope of work for this study included:  Reviewing historical site explorations (Hart Crowser, 1985) within the south-central portion of the site where a multi-story residential building/garage will be located.  Completing two mud-rotary borings within the planned area of a multi-story Sound Transit garage structure in the northern portion of the site.  Collecting boring soil samples and performing laboratory index tests on representative samples.  Evaluating subsurface conditions and site liquefaction potential.  Completing geotechnical engineering analyses and providing geotechnical design recommendations for: • Building foundation options, including augercast (AC) piles and ground improvement/shallow foundations; • Structural/Slab-on-grade concrete floors; • Asphalt pavement sections for new parking areas and access roads; • Seismic design criteria; • Subsurface drainage; • On-site stormwater infiltration feasibility; and • Structural fill.  Summarizing our findings in this report. We completed this work in general accordance with the scope of work in our master services agreement and Statement of Work with the Port Quendall Company, dated January 22, 2019. This report was prepared for the exclusive use of the Port Quendall Company, Vulcan Real Estate, and their design consultants and construction contractors, for specific application to the subject project and site. We completed this study in accordance with geotechnical practices generally accepted for work of a similar nature done in the same timeframe, in the same or similar localities, and under similar conditions. No other warranty, express or implied, is made. SITE AND PROJECT DESCRIPTION The project site is located at the former Pan Abode Redevelopment Sitesite located at 4350 Lake Washington Boulevard in Renton, Washington, as shown on Figure 1 (Vicinity Map). Current site development plans call for demolition of the existing structures and construction of three four-story, at- grade, residential building/garage with a footprint area on the order of 31,256 square feet (sf), 19,681 sf, DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 2 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 and 17,614 sf located in the north, southeast, and southwest portions of the site, respectively. This building is expected to consist of a concrete garage core with a wrap-around, wood-framed residential structure. A multi-story, elevated Sound Transit garage with a roughly 30,000 sf footprint area is also planned within the northern portion of the site, along with two smaller, single-story buildings (daycare and flexible space). All these structures will be surrounded by associated asphalt car parking/driveways and landscaping areas. The existing ground surface generally ranges from an elevation of 30 to 33 feet across the site, and planned developed grades are expected to be similar. We understand that finished slab-on- grade elevations have not yet been determined for the structures. The general layout of the proposed site development is shown on Figure 2 (Site and Exploration Plan). Structural and architectural details and loading requirements of the planned buildings are not currently known. Because of the settlement-prone subsurface conditions (loose to medium dense site soils and potential soil liquefaction), the building foundation system is expected to consist of either pile-supported building/floors or shallow foundations and slab-on-grade over a ground improvement (GI) subgrade. We understand that the project was reactivated in January 2021 and the proposed redevelopment plan has changed. We have reviewed the changes to the site plan and provide updated engineering recommendations. Based on our review of the latest redevelopment configuration, dated January 19, 2021, we understand the project will now include three above-grade parking structures located at the north, southeast, and southwest zones of the site. The site redevelopment will also include several four-story wood structures and surface pavement. GENERALIZED SUBSURFACE CONDITIONS Our understanding of the subsurface conditions at the proposed office building site is based on data from field explorations, soil laboratory tests, and a review of historical boring logs from a previous Hart Crowser site subsurface investigation in 1985. Current exploration logs, laboratory test results, and historical exploration logs are presented in Appendices A, B, and C. The historical borings were generally advanced up to a depth of 65 feet below existing ground surface (bgs) within the central portion of the site, and included two groundwater monitoring wells (not visible today). In March 2019, we advanced two mud-rotary borings (HC-B1, HC-B2) near the outside corners of the proposed Sound Transit garage in the north portion of the site, to supplement the historical explorations (see Figure 2 for locations). A groundwater monitoring well was installed at boring location HC-B2. The current explorations in the north portion of the site generally confirmed similar subsurface conditions to the central portion of the site (from historical logs), indicating relatively uniform subsurface conditions across the site. The explorations reveal subsurface conditions only at discrete locations across the project site, and actual conditions in other areas could vary. Furthermore, the nature and extent of any such variations will not become evident until additional explorations are performed or until construction activities begin. If significant variations are observed at that time, we may need to modify our conclusions and recommendations in this report to reflect the actual site conditions. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 3 19442-00 May 20, 2021 Site Soils The near-surface soil conditions within the central portion of the site (proposed residential building area) is generally composed of 1 to 2 feet of historical fill over about 15 feet of interlayered, soft to medium stiff silt and loose to medium dense sand/silty sand with variable amounts of gravel and trace organics. These soft/loose upper soils appear to extend slightly deeper into the northern portion of the site (20 to 25 feet bgs). Below these soft/loose to medium stiff/medium dense upper soils, our current and historical borings encountered dense to very dense, interlayered sand, silty sand with gravel, and silty/sandy gravel with cobbles. These dense underlying soils are interpreted as glacially overconsolidated and considered suitable for support of deep foundations (i.e., soil bearing layer). Groundwater Generally, the historical explorations (September 1985) within the central portion of the site indicate a groundwater level ranging from 4 to 9 feet bgs (generally between elevations of 24 to 27 feet). Current groundwater monitoring well readings (March 25, 2019) in HC-B2 and an undocumented well within the northeast portion of the site indicate a static groundwater level ranging between 2 to 3.5 feet bgs (corresponding to an elevation of 30 feet). We interpret the higher current groundwater level readings to be reflective of seasonally high conditions during the wetter winter/late spring months. Similarly, high seasonal groundwater conditions are expected to also exist across other portions of the development site. Groundwater levels presented herein were observed at the times indicated on the exploration logs. Throughout the year, groundwater levels are expected to fluctuate in response to changing precipitation patterns, off-site construction activities, changes in site use, or other factors. SEISMIC DESIGN CONSIDERATIONS The site is located in a seismically active area. In this section, we describe the seismic setting for the project site, discuss seismically induced geotechnical hazards, and provide code-based seismic design parameters. We understand the seismic design of the proposed structure will be based on the 2018 International Building Code (IBC). Seismic Setting The seismicity of western Washington is dominated by the Cascadia Subduction Zone , in which the offshore Juan de Fuca plate is subducting beneath the continental North American plate. Three main types of earthquakes are typically associated with subduction zone environments—crustal, intraplate, and interplate earthquakes. The U.S. Geological Survey (USGS) earthquake database used to develop probability based seismic design parameters includes all three types of earthquakes. Recent fault trenching and seismic records in the Puget Sound area clearly indicate a distinct shallow zone of crustal seismicity (e.g., the Seattle and Tacoma Fault Zones) that may have surficial expressions and can extend to depths of up to 25 to 30 kilometers. A deeper zone is associated with the subducting Juan de Fuca plate and produces intraslab earthquakes at depths of 40 to 70 kilometers beneath the Puget Sound DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 4 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 region (e.g., the 1949, 1964, and 2001 earthquakes) and interplate earthquakes at shallow depths near the Washington coast (e.g., the 1700 earthquake with an approximate magnitude of 8 to 9). Seismically Induced Geotechnical Hazards Potential for seismically-induced geotechnical hazards in a seismically active area generally include surface fault rupture, soil liquefaction, and lateral spreading. The risks associated with each, relative to the project site, are discussed in this section. Surface Fault Rupture The project site is located within less than a mile of the mapped Class A Seattle Fault Zone (USGS Interactive Fault Map; https://earthquake.usgs.gov/hazards/qfaults/; accessed April 12, 2019), which runs roughly in a northwest to southeast direction through the southern end of Mercer Island. Because of the relatively close distance from this fault zone, there is a potential of surface rupturing at the project site. However, we consider the risk of surface damage from potential rupturing at the Pan Abode site to be relatively low, given the distance to the mapped fault and the significant amount of sediment underlying the site (at least 75 feet, based on explorations). This relatively thick sediment layer will tend to reduce the potential surface impact of possible bedrock rupturing at depth. Soil Liquefaction Liquefaction is a phenomenon caused by a rapid increase in porewater pressure that reduces the effective stress between soil particles, resulting in the sudden loss of shear strength in the soil. Granular soils that rely on inter-particle friction for strength are susceptible to liquefaction until the excess pore pressures can dissipate. Sand boils and flows observed at the ground surface after an earthquake are the result of excess pore pressures dissipating upward, carrying soil particles with the draining water. In general, loose, saturated sandy soils with low silt and clay contents are the most susceptible to liquefaction. Silty soils with low plasticity are moderately susceptible to liquefaction under relatively higher levels of ground shaking. For any soil type, the soil must be saturated for liquefaction to occur. Liquefaction can cause ground surface settlement, lateral spreading, or slope displacement, depending on the site-specific topographical conditions. Given the presence of potentially liquefiable soil conditions in our explorations, we performed a site-specific soil liquefaction evaluation using the standard penetration test (SPT) based procedures outlined by Idriss and Boulanger (2008), using soil laboratory test data. We assumed an earthquake magnitude of 7.1 and a site class adjusted surface peak ground acceleration (PGA) of 0.537 for a 2,475-year seismic event, in accordance with the current IBC (2018 IBC). The results of our analysis indicate that significant portions of the soft fine-grained soils and loose to medium-dense sandy soils in the upper 15 to 25 feet bgs are susceptible to liquefaction during the anticipated design earthquake event (2018 IBC). The corresponding post-liquefaction settlement is estimated to be on the order of 3 to 9 inches (or more) across the site. Liquefaction is not expected to occur within the dense to very dense sand/gravel bearing soils at depth. Liquefaction-induced surface DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 5 19442-00 May 20, 2021 settlement is not typically uniform across the area and can therefore result in significant differential settlement. Lateral Spreading Lateral spreading refers to horizontal ground movement caused by gravity-induced, lateral flow failure of the liquefied soil mass on gently sloping terrain or near steeply sloping ground along bodies of water (shorelines or river banks). Lateral movement of the ground surface under liquefied soil flow conditions may be large and can lead to cracking and separation of the ground surface. This can significantly affect the stability of shallow foundations and lateral loading on the upper portion of pile-supported foundation systems. Because the current and planned development is relatively level and not near a steep slope, the risk of potential lateral spreading is considered very low at this site. Seismic Design Parameters The basis of seismic design for the 2018 International Building Code (IBC) is the risk-targeted maximum considered earthquake (MCER) which is used to determine spectral response accelerations. The peak ground acceleration (PGA) is determined using the maximum considered earthquake geometric mean (MCEG). The MCER ground motion response accelerations are defined for the most severe earthquake considered by IBC 2018, determined for the orientation that results in the largest maximum response to horizontal ground motions, and adjusted for the targeted risk. The geometric mean PGA corresponding to MCEG is defined for the most severe earthquake without adjustment for the targeted risk. The most severe earthquake considered by the IBC has a 2 percent probability of exceedance in 50 years, corresponding to a 2,475-year return period. The mapped response spectra are based on Site Class B (rock) conditions. Seismic parameters are adjusted based on the actual site conditions, generalized as the soil site class. IBC 2018 defines the design spectral acceleration parameters at short periods (SSD), and at the one-second period (S1D) as two-thirds of the corresponding site-class-adjusted MCER parameters (SMS and SM1). Similarly, ASCE 7-16 requires MCEG peak ground acceleration adjusted for site effects (PGAM) to be used for evaluation of liquefaction, lateral spreading, seismic settlements, and other soil-related issues. Based on the soil conditions, the seismic Site Class without consideration of liquefaction is Site Class D. Because a liquefaction hazard exists at the site, the site becomes Site Class F with the exception that if the building period is less than 0.5 seconds, the site may be considered Site Class D per Section 20.3.1 of ASCE 7-16. We understand that the building period is less than 0.5 seconds. The seismic design parameters for this site were obtained from the USGS U.S. Seismic Design Maps web application (https://earthquake.usgs.gov/ws/designmaps/asce7-16.json?latitude=47.53036&longitude=- 122.19932&riskCategory=II&siteClass=D&title=PanAbode_1944200), accessed on March 31, 2021. The DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 6 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 seismic design parameters are provided in Table 1. Please refer to the discussion following this table before using these parameters. Table 1 – Building Code Seismic Design Parameters Parameter Value Site Class D Latitude 47.53036 Longitude -121.19932 Peak Ground Acceleration (PGA) 0.678 g MCE Spectral Response at Short Periods (Ss) 1.442 g MCE Spectral Response at 1-Second Period (S1) 0.497 g Site coefficient for PGA (Fpga) 1.100 Site coefficient for Short Periods (Fa) 1.000 Site coefficient for 1-Second Period (Fv) 1.803a Notes: a.Use of the parameters in this table requires the use of Exception 2 in ASCE 7-16 Section 11.4.8. Also reference ASCE 7-16 Supplement 1 Table 11.4-2. ASCE 7-16 Section 11.4.3 requires a ground motion hazard analysis for Site Class D sites with S1 greater than 0.2 unless Exception 2 in Section 11.4.8 is taken. The exception requires the seismic response coefficient CS be determined by Eq. (12.8-2) for values of T ≤ 1.5 TS and be taken as equal to 1.5 times the value computed in accordance with Eq (12.8-3) for TL ≥ T > 1.5 TS or Eq. (12.8-4) for T > TL. It is important to note that the seismic response coefficient (Cs) must be increased as described in ASCE 7-16 to take advantage of the code exception. These modifications are generally significant for taller structures with periods of 0.5 seconds or greater. The assumptions and requirements of Exception 2 should be communicated to the structural engineer and project team. Alternatively, Hart Crowser may be contracted to perform a ground motion hazard analysis to produce a site-specific response spectrum upon request. GEOTECHNICAL CONCLUSIONS AND RECOMMENDATIONS This section of the report presents our conclusions and recommendations for the geotechnical aspects of building design and site development. Our geotechnical investigation and engineering analysis have been performed in accordance with generally accepted geotechnical practices. We have developed our conclusions and recommendations based on our current understanding of the project. If the nature or location of the project is different than we have assumed, Hart Crowser should be notified so we can confirm or modify our recommendations. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 7 19442-00 May 20, 2021 General Considerations The soft to medium stiff fine-grained and loose to medium dense granular near-surface soils at this site are compressible/potentially liquefiable and not generally considered suitable to directly support shallow building foundations. Given these subsurface conditions, we recommend the multi-story building foundations and floor slabs are supported either on deep pile foundations bearing in the non-liquefiable, denser sand layer at depth, or on shallow foundations bearing on ground improvement (GI) subgrade soils. Alternatively, the smaller, single-story buildings may be supported by a reinforced, floating slab-on-grade floor/foundation system, if the structural engineer deems this approach adequate to meet the seismic life and safety design requirements in the building code. Based on our experience with similar site developments and subsurface conditions, we recommend AC piles as the most suitable and cost-effective deep foundation system for this project. Given the expected building type/size and subsurface conditions at this site, we anticipate that 16- to 18-inch- diameter AC piles will likely provide suitable bearing capacity for this project. However, larger diameter AC piles could be considered if higher pile capacities than those provided in this report are required. Alternatively, GI may be used to reinforce the soft site soils and provide shallow foundation and slab-on-grade bearing support of the planned building, if cost-effective and feasible to the non-liquefiable soil depth at this site. GI techniques typically consist of gravel-filled, vertical elements that increase the surrounding soil stiffness and improve subsurface drainage. This greatly reduces the potential static/seismic settlement, allowing the use of shallow foundations and slab-on-grade floors (or a combined floor/column concrete mat foundation). Because of their proprietary nature, a GI system is typically incorporated as a design-build component of the construction plans, meeting certain design/construction criteria specified by the geotechnical and structural engineers (such as seismic assumptions and tolerable building settlements). Both of these foundation/floor slab support options are discussed in greater detail in the subsequent sections of this report, along with our general geotechnical design and construction recommendations. Provided that planned grades are the same or less than the existing ground surface (i.e., no additional fill to raise grades), potential long-term settlement of the soft/organic near-surface fine-grained soil within landscaped and paved areas around the planned buildings should be negligible. If a significant amount of fill is required to raise grades (generally more than 1 foot), HC should be allowed to review the location-specific potential for future settlement and provide mitigation measures, if necessary. Site Preparation and Grading Site preparation should provide a firm and non-yielding subgrade beneath footings, slabs-on-grade, new structural fill, and pavement sections. Initial site preparation will involve stripping existing pavement and vegetation, demolishing existing structures, removing existing foundation and floor elements, and abandoning in place or removing any underground utilities within the new building area. We recommend intercepting and diverting any potential sources of surface or near-surface water within the construction zones before stripping begins. Because the selection of an appropriate drainage system DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 8 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 will depend on the water quantity, season, weather conditions, construction sequence, and contractor’s methods, final decisions about drainage systems are best made in the field at the time of construction. Nonetheless, we anticipate that curbs, berms, or ditches placed along the uphill side of the work areas will generally intercept surface water runoff during construction. After surface and near surface water sources have been controlled, the construction areas should be cleared and stripped of all vegetation, topsoil, debris, asphalt, and concrete. All prepared structural or pavement subgrade areas should be observed and approved by a representative of Hart Crowser. Visible organic material (sod, humus, roots, and/or other decaying plant material), debris, and other unsuitable material should be removed from the subgrade areas. The prepared subgrade should be inspected for soft areas, if necessary, by proof rolling with a fully loaded tandem-axle dump truck. Any identified soft areas should be overexcavated to firm subgrade and backfilled with properly compacted structural fill. Some of the subgrade soils revealed after stripping and cutting to subgrade elevation may consist of fine-grained, moisture-sensitive soils; care should be taken to protect these areas from rain and runoff water. Construction traffic should be avoided across moisture-sensitive subgrade soil areas during wet weather. We recommend site stripping and excavation be performed using a straight-edged bucket mounted on an excavator that does not traverse the final subgrade. Partial overexcavation may be required locally if unsuitable, organic-rich, or debris-laden fill material is encountered within new structural subgrade areas. We recommend any existing structures such as concrete foundations, slabs, or pile foundations be removed within 2 feet below the base of any new foundation, slab-on-grade, or pavement section. The purpose of this is to avoid uneven or inconsistent “hard spots” or ridges, which could lead to undesirable differential settlement beneath new structural elements. If feasible and cost-effective, existing concrete foundations/slabs may be crushed on site and recompacted as structural fill, under observation of the geotechnical engineer in the field. Ideally, the demolished concrete should be crushed to a maximum 2-inch size, to be suitable for recompaction, in accordance with our structural fill recommendations. If the existing warehouse building is pile-supported, the piles from the old structure may generally be left in place if they are not interfering with the locations of new pile elements and are more than 2 feet below the bottom of the proposed new foundations or concrete floor slab. We recommend reviewing the existing building plans, if available, to estimate the potential impact of the existing foundation system on the proposed development. It may be necessary to relocate or abandon some utilities. Abandoned underground utilities should be removed or completely grouted. The ends of remaining abandoned utility lines should be sealed to prevent piping of soil or water into the pipe. Soft or loose backfill materials should be removed and replaced, according to the structural fill recommendations in this report. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 9 19442-00 May 20, 2021 Augercast Pile Foundations Given the required depth to non-liquefiable bearing soil and the anticipated structural loading requirements, we recommend steel-reinforced AC piles as the most suitable and cost-effective deep foundation system for this project. The following sections provide our design recommendations and installation criteria for AC piles. Vertical AC Pile Capacity (Compressive and Uplift) For the anticipated subsurface conditions and structural loading requirements, we recommend using 16- to 18-inch-diameter AC piles. The bearing capacity of these piles will be achieved primarily from end bearing and frictional resistance within the deeper, dense to very dense sand/gravel bearing soil layer below the potentially liquefiable upper soils. Based on the referenced current and historical site explorations, the top of this sand bearing layer is expected to be located around a 15 foot elevation (NAVD88) within the southern portion of the site, and at gradually lower elevations going northward (decreasing to ‒5 feet near the north end of the site). This top-of-bearing soil layer surface is depicted by the elevation contour lines shown in Figure 2. We assumed in our bearing capacity analyses that the AC piles would penetrate a minimum of ten times the AC pile diameter, or 10 to 15 feet into the bearing layer for 16- and 18-inch AC piles, respectively. If unexpected subsurface conditions or top-of-bearing elevations are encountered during construction, pile lengths may need to be adjusted, based on actual drilling conditions observed in the field. Therefore, we recommend including an allowance in the contract documents for a unit cost adjustment (per foot), if longer or shorter AC piles are required. Our recommended vertical AC pile capacities for the minimum pile embedment into bearing soil discussed above are presented in Table 2 below. For design flexibility, we have also provided additional capacity if the piles are extended deeper than the minimum recommended (in 5-foot increments). The AC contractor should confirm that the final depths specified by the structural engineer are achievable with the installation methods they propose to use. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 10 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 Table 2 – Vertical AC Pile Capacities (Compressive and Uplift) AC Pile Diameter (inches) Pile Embedment into Bearing Soil Layer (feet) a Static Compressive (tons) b, c Seismic Compressive (tons) d Seismic Uplift (tons) d 16 15 75 65 26 Each Additional 5 feet Deeper +7 +9 +9 18 15 90 75 30 Each Additional 5 feet Deeper +8 +11 +11 Notes: a. See Figure 2 for estimated top of bearing layer elevations. b. Factor of Safety = 2.0. c. Maximum static compressive capacity may be limited by structural pile considerations; we recommend not exceeding 90 and 100 tons, respectively, for 16- and 18-inch diameter piles, pending review by structural engineer. d. Factor of Safety = 1.5 for transient, short-term loading condition. Assumes coupled seismic analysis, with soil liquefaction occurring during seismic loading (i.e., no frictional resistance within and above liquefied soil layers). The vertical compressive and uplift capacities for AC piles presented in Table 2 are presented only as they relate to the frictional resistance and bearing capacity of the soil. The structural engineer should also verify the AC piles are structurally capable of supporting these pile capacities and lengths, in accordance with applicable building code requirements. Pile Downdrag Loads Downdrag loading typically occurs when soil settles around installed piles, either from static soil consolidation or following post-liquefaction settlement (seismic downdrag). The downward movement of the soil relative to the pile causes negative shaft resistance to act on the pile, which will add to the vertical compressive load on the pile. Downdrag loads should be considered a structural load on the pile, in addition to the building/structure loads supported by the pile. Based on the proposed development, static downdrag loading is not expected to occur at this site. However, seismic downdrag will likely occur due to the anticipated soil liquefaction during the design earthquake event. We estimate the seismic downdrag load at this site will be on the order of 18 tons (16- and 18-inch-diameter AC piles) within the northern portion of the site where the upper liquefaction zone may be up to 30 feet deep (Sound Transit garage location). Within the southern portion of the site, where the potential liquefaction zone is expected to be on the order of 15 to 20 feet deep (main residential/garage structure location), we estimate seismic downdrag loads will be on the order of 11 tons for the same pile diameters. We recommend the structural engineer incorporate these additional seismic downdrag loads in their pile design, and verify the combination of the building design load and the downdrag load is less than the allowable pile capacity based on soil bearing. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 11 19442-00 May 20, 2021 Lateral AC Pile Loads Lateral loads, which may be imposed on the piles by transient wind and/or earthquake forces, are resisted primarily by the horizontal bearing support of soil against the pile shaft. The resistance to lateral loads depends on the pile length, stiffness in the direction of loading, and degree of fixity at the head, as well as the adjacent soil properties. Deflection of laterally loaded piles is greatest at the head and gradually decreases with depth. The depth along a pile shaft at which deflection becomes insignificant is referred to as the depth of fixity. The lateral pile capacity is typically determined based on the allowable deflection criteria of the structure. The lateral deflection of the pile, in turn, depends primarily on the soil conditions within the upper portion of the pile shaft, and whether it is structurally fixed at the top (e.g., supported by grade beams) or not. Computer software programs (Ensoft LPILE, or similar) are commonly used to estimate the response of piles to lateral loads. For AC piles, the LPILE analysis requires input parameters that depend on the structural behavior of the concrete/grout and reinforcement used (such as the use of a reduced, cracked moment of inertia). Therefore, this is best performed by the structural engineer. For such lateral LPILE analyses, we recommend using the input parameters for a standardized soil profile, provided in Table 3 below. Using these static soil resistance values assumes a decoupled seismic analysis, with soil liquefaction occurring after the initial seismic loading. If a coupled seismic analysis is required, appropriate liquefied soil p-multipliers should be used in the LPILE analyses to model the reduced liquefied strength within the sand layers, as recommended by Washington State Department of Transportation (WSDOT; Brandenberg, 2007). Table 3 – LPILE Soil Parameters Elevation (feet, NAVD88) a Soil Unit Effective Unit Weight (pcf)a Friction Angle (deg) Kunsat (pci) Ksat (pci) North Parking Garage Main Residential Building USCS p-y Model Above 28 Above 30 SM API Sand 125 33 140 - 15 to 28 15 to 30 SM API Sand 65 33 - 80 10 to 15 N/A SM/GM API Sand 70 36 - 90 5 to 10 N/A ML API Sand 60 30 - 50 0 to 5 N/A SP/SM API Sand 70 36 - 200 Below 0 Below 15 SM/GM API Sand 75 42 - 250 Notes: a. Design groundwater level was generally assumed at 2 feet below existing ground surface. Pile Group Effects The estimated pile design values and recommendations provided above for compressive, uplift, and lateral loading conditions refer to single piles unaffected by group interactions. Generally, if piles are spaced at DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 12 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 least three diameters apart (center-to-center), group effects can be ignored for compressive, uplift, and perpendicularly applied lateral loads. For in-line lateral loads, group effects can be ignored at a pile spacing of eight diameters or more. For piles installed at this spacing or greater, pile group capacities can be considered to be the sum of the individual pile capacities, i.e., no reduction factor is applied to individual pile capacities. For laterally loaded pile groups where the spacing is closer than eight pile diameters, group reduction factors (p-multipliers) should be used in the LPILE analysis to model the effects of group interaction. Table 4, below, presents our recommended p-multipliers for typical pile group spacings (as a function of pile diameter). Table 4 – LPILE Group Reduction Factors (P-Multipliers) Relative Location of Pile P-Multiplier based on Pile Spacing (center to center) 3B b 4B 5B First Rowa 0.8 0.85 0.9 Second Row 0.55 0.7 0.8 Trailing Rows 0.4 0.55 0.7 Notes: a. The first row is the leading pile row pushing against the soil in the direction of the load (furthest away from the load application point). b. B = pile diameter. For piles that must be installed closer than 3 pile diameters, Hart Crowser should be contacted to provide further review and recommendations for closely spaced piles. Pile Cap and Grade Beam Passive Resistance In addition to lateral resistance offered by the piles, properly backfilled footings, grade beams, and stemwalls will also resist lateral movement by means of passive earth pressure. We recommend designing these for an allowable passive soil resistance of 250 pounds per cubic foot (pcf), expressed as an equivalent fluid density (EFD) and acting over the embedded portion of the proposed grade beams (neglecting the upper 1 foot bgs). This passive resistance assumes unsaturated soil conditions and a safety factor of 1.5, and may be increased by one-third for short-term loads such as wind or earthquake. Pile Settlement We estimate that total post-construction settlement of properly designed and installed AC piles will be on the order of 1/2 inch or less. Differential settlement between adjacent pile caps, pile groups, and/or grade beams could approach two-thirds of the actual total settlement. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 13 19442-00 May 20, 2021 AC Pile Installation Considerations We recommend the installation of AC piles be observed by a Hart Crowser representative. Our representative would collect and interpret installation data, verify adequate installation methods, confirm actual soil conditions are consistent with those expected, and verify the required pile embedment depths have been achieved. As the completed pile is below the ground surface and cannot be observed during construction, judgment and experience must be used to aid in determining the acceptability of the pile. This also requires use of an AC pile contractor who is familiar with such installation. We recommend close monitoring of installation procedures such as installation sequence, auger withdrawal rate, grouting pressure, and quantity of grout used per pile. Variations from the established pattern, such as low grout pressure, excessive settlement of grout in a completed pile, etc., would make the pile susceptible to rejection. We recommend the following minimum requirements for AC pile installation:  The contractor should provide a pressure gauge in the grout line between the pump and the auger, which should indicate a continuous minimum pressure of 100 pounds per square inch (psi) during the entire installation operation.  The contractor should provide a means of determining the quantity of grout used per pile, such as a calibrated stroke counter on the grout pump.  To provide a continuous grout column with the required AC pile diameter, clockwise auger rotation and a minimum 10-foot grout head above the bottom of the auger should be maintained, uninterrupted, during the entire installation operation.  To minimize the risk of grout loss from adjacent piles, the contractor should be required to schedule the installation of piles such that no piles within five pile diameters of each other are drilled within a 24-hour period. Pressure grouting during AC installation typically results in a grout column that is slightly larger than the nominal diameter of the drilled hole. Within the soft fine-grained soil and loose to medium dense sand in the upper 15 to 30 feet bgs, we anticipate grout volumes may be on the order of 1.2 to 1.5 times the nominal pile volume, or more. Grout volumes are likely to be less within the denser bearing soils at depth. Note that obstructions (such as buried pile/foundation elements) may be encountered within previous building footprint areas during drilling, as discussed previously in the Site Preparation section of this report. This may require pile relocation and potential reevaluation and field adjustment of the pile cap design by the structural engineer. Difficult drilling conditions may also be encountered, and should be anticipated, within the medium dense to dense sand layers at depth, which were found to be gravelly in some areas of the site (may also include cobbles and boulders). DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 14 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 Ground Improvement (GI) Ground improvement (GI) construction techniques, such as rammed aggregate piers (RAP) or stone columns (herein referred to as “aggregate piers”), may be used to improve the weak/liquefiable ground conditions and allow the use of conventional spread foundations and slab-on-grade floors. The GI design and installation are typically completed by a specialty design-build contractor. In this section, we provide our recommended baseline performance guidelines for GI design and bidding purposes. Other GI methods (such as jet ground shear panels) may be used to mitigate liquefaction, but are not explicitly described below. Based on our preliminary review, aggregate pier elements will likely need to extend to depths ranging from approximately 15 to 30 feet below planned building floor slab subgrade level, to limit potential static and seismic settlements to tolerable levels (generally to top of pile bearing layer elevations shown on Figure 2). This may approach the maximum depth possible for the use of GI construction techniques. We, therefore, recommend contacting GI design-build contractors early in the foundation design process to evaluate if the use of aggregate piers is feasible and cost-effective at this site. Aggregate piers are constructed by vibrating or pushing a large mandrel into the ground to the bottom of the improvement zone, and backfilling the resulting hole with rock. In the case of stone columns, free-draining rock is passed through the mandrel and into the column cavity. The mandrel is withdrawn and reinserted in intervals (typically 3 feet) to provide vibratory or pneumatic compactive effort. In the case of RAP, rock is dumped from the surface into the cased or open hole and then compacted in 1- to 2-foot intervals. These aggregate piers provide liquefaction mitigation through soil densification, stress redistribution, and/or improved drainage. As previously discussed, obstructions (such as buried pile/foundation elements) may be present within the existing building footprint areas, and should be considered as part of the GI design and construction planning. Difficult drilling conditions may also be encountered, and should be anticipated, within the medium dense to dense, silty sand/gravel layers (including potential presence of cobbles and boulders). General GI Design Criteria The specialty contractor should optimize the ground improvement design/installation method, depth, and spacing based on a review of the available subsurface information in this report. We recommend the aggregate piers be designed to mitigate liquefaction and ground settlement/consolidation beneath all foundation and floor slab elements. The aggregate pier GI shall extend a distance outside the building perimeter, as deemed necessary by the GI designer (but no less than 10 feet) to protect the building foundation system from the effects of liquefaction. We anticipate the aggregate piers will have a target depth of up to approximately 30 feet below planned building floor slab subgrade level and will be concentrated along footing lines and beneath structural columns, with additional aggregate piers beneath floor slab areas. As the aggregate piers are constructed, they may densify the surrounding soils, provided those soils do not contain excessive amounts of fine-grained materials (i.e., silt or clay). At this site, it shall be assumed that the upper portion of the improvement zone (approximately elevation 25 feet) consist of medium dense DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 15 19442-00 May 20, 2021 silty sand to silty sand with gravel and trace of organic materials in the near surface materials. A relatively thin (5 to 10 feet thick) layer of silt with sand (ML) shall be assumed present just above the bearing layer in the northern portion of the site (Sound Transit garage location). Laboratory test results indicate this silt layer generally contains 60 percent fines by mass, while the granular soils above may contain up to 25 percent fines. The densification and drainage effects from ground improvement are likely to be limited, and aggregate pier design will likely need to rely primarily on stress redistribution, within the fine-grained soil layers. Vibrations generated during aggregate pier construction can also cause deterioration and softening of soft fine-grained soils. The GI designer should consider the potential for (and provide measures to control) this in the design and installation of the piers. The GI design should follow the design techniques/considerations in the Commentary Guidelines for Ground Improvement using Discrete Elements (2016), developed by the Seattle Section Geotechnical Group of the American Society of Civil Engineers (ASCE) and the City of Seattle Department of Construction and Inspections. We recommend the ground improvement system be designed to target the following minimum performance criteria (should be reviewed and modified, if needed, by structural engineer):  A minimum allowable bearing pressure of 3,000 pounds per square foot (psf), with an allowable one-third increase for seismic loading;  A total static settlement (including construction settlement) of less than 1 inch, with differential settlement over a 50-foot span of less than 1/2 inch (including short-term primary and long-term secondary soil settlement);  A seismically induced settlement less than 1.5 inches with differential settlement over a 50-foot span of less than 0.75 inches;  A minimum allowable frictional coefficient of 0.35 for sliding resistance along the footing base;  A minimum modulus of subgrade reaction (kv) of 125 psi per inch to support concrete slabs-on-grade with up to 200 psf floor loading.  An overall density increase of the ground improved zone to change the IBC Site Class from F to D (or better). The GI design shall identify the final site class achieved by the design, and shall verify this new site classification with pre/post-construction cone penetration test (CPT) soundings. GI Design Methodologies and Quality Control Supplementing the general design criteria described above, we recommend the following additional quality control measures for aggregate pier design and installation:  The ground improvement design-build contractor should submit design plans and design calculations stamped by a professional engineer licensed in the state of Washington, including the final aggregate pier layout and installation details (i.e., pier depths, diameter, spacing, and pattern). The design DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 16 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 calculations shall be based on the subsurface conditions and the minimum design criteria described in this report.  The aggregate pier design shall use the Rayamajhi et al. (2012) methodology to evaluate the stress redistribution. We recommend Barksdale and Bachus (1983) methodology to evaluate densification effects, or alternative methods supported by data in similar soils and using same installation techniques as proposed. Strain compatibility analysis methods (such as Baez and Martin, 1993) shall not be used.  All soils above the top of pile bearing layer elevations shown on Figure 2 shall be considered potentially liquefiable, and shall be evaluated by the GI designer using the Boulanger and Idriss (2014) analysis methodology.  The GI design and installation method should consider/address the potential for groundwater seepage during aggregate pier construction.  We recommend Hart Crowser be retained to review the final aggregate pier design.  The contractor’s ground improvement design should include appropriate field verification testing to evaluate the effectiveness of the ground improvement, and to verify the specified performance criteria have been met. Standard-of-practice verification methods typically include pre- and post-ground improvement CPT soundings to the bottom of the improvement zone, and aggregate pier load testing. The final verification test results should be submitted to Hart Crowser for review and approval. The number of verification tests should be determined by the designer based on the ground improvement area and number of aggregate piers installed, but should not be fewer than two CPT sounding verification locations (with pre- and post-installation CPT at each) and one plate load test for each proposed structure. Alternative confirmation methods proposed by the specialty contractor shall be reviewed and approved by Hart Crowser prior to use.  Hart Crowser should be retained to provide field observation of the aggregate pier installation, to verify and document proper installation methods. GI Building Subgrade Preparation The footing and slab design recommendations presented subsequently assume the ground improvement subgrade is undisturbed and prepared according to the ground improvement plan. Any loosening of subgrade materials before concrete is placed could result in settlement exceeding the specified design tolerance. Therefore, it is important to clean all loose or disturbed soil from foundation excavations and remove standing water before placing concrete. A 6- to 12-inch-thick stabilization layer of compacted, select fill (clean sand and gravel or crushed rock) is sometimes specified to protect the prepared, ground improvement subgrade from potential disturbance during construction (especially during the wet season or wet weather/site conditions). Given the presence DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 17 19442-00 May 20, 2021 of near-surface, relatively fine-grained soil and shallow groundwater conditions, this approach may be advisable at this site. The contractor GI designer should consider and determine the need for a stabilization layer or load transfer platform as part of their design, based on their interpretation of the subsurface information presented in this report and the GI design methods used. Shallow Foundations If the site soils are improved using aggregate piers, conventional shallow spread footings can be used to support the proposed office building. Alternatively, the smaller, single-story buildings may be supported by a reinforced, floating slab-on-grade floor/foundation system (i.e., mat foundation), if the structural engineer deems this approach adequate to meet the seismic life and safety design requirements in the building code. We make the following recommendations for design of footings (or reinforced mat foundation) bearing on a suitable ground-improved subgrade:  All footings should bear directly on the rammed aggregate pier elements, or a crushed rock working surface (if used) placed directly on the pier elements.  The allowable footing bearing pressure, sliding resistance to lateral loads, and foundation settlement will ultimately be determined by the contractor’s GI design. However, the minimum design criteria noted above may be used for preliminary planning and design purposes.  For frost protection, exterior and interior footings should bear a minimum of 18 and 12 inches below exterior grade and finished floor elevation, respectively.  New continuous (strip) and isolated footings should be designed with a minimum width of 1.5 and 2.5 feet, respectively.  Footings should bear outside (below) an imaginary 1 horizontal to 1 vertical (1H:1V) plane projected upward from the bottom edge of adjacent footings or utility trenches, to avoid surcharging adjacent structures or excavations.  Resistance to lateral loads on the shallow footings may be provided by passive earth pressure acting against the sides of the footings. An allowable passive resistance of 250 pcf (EFD) may be used for this design, acting over the embedded portion of the footing and stem wall (neglecting the upper 1 foot). This passive resistance assumes a safety factor of 1.5, and may be increased by one-third for short-term loads such as wind or earthquake.  Hart Crowser should be on site to assess and document the suitability of the footing subgrade condition during construction, and to recommend appropriate measures to improve unsuitable subgrade conditions, if needed. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 18 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 Concrete Slab-on-Grade Floors Conventional concrete slab-on-grade floors are generally considered feasible on an aggregate pier GI subgrade, provided the subgrade surface is properly prepared according to the ground improvement plan and as recommended in this report. We recommend the following design and subgrade preparation criteria for slab-on-grade floors (or reinforced mat foundation).  Place and compact a minimum thickness of 6 inches of pea gravel, washed rock, or other uniformly graded gravel below the floor slab to serve as a leveling course and capillary break, to reduce the risk of potential floor moisture problems. This free-draining capillary break material should contain less than 3 percent by weight passing the U.S. No. 200 mesh sieve, based on the minus 3/4-inch fraction. WSDOT Gravel Backfill for Drains, Section 9 03.12(4), would be a suitable capillary break material.  Place a vapor barrier above the capillary break material to minimize moisture penetration through the concrete slab, which can compromise certain finished floor materials.  The slab-on-grade subgrade surface below the concrete floor capillary break layer should be prepared according to the ground improvement plan and as recommended in this report. Disturbed soils should be removed and replaced with structural fill as described in this report.  The concrete slab design should be based on a vertical modulus of subgrade reaction (KV1) appropriate for the aggregate pier diameter and spacing used in the contractor GI design, and meeting the minimum design criteria recommended above.  We recommend a representative of Hart Crowser observe exposed floor subgrade areas during construction to confirm suitable floor support conditions, or to recommend appropriate measures to improve unsuitable slab subgrade conditions, if needed. Building Drainage Considerations We generally recommend slab-on-grade buildings be provided with a perimeter drain system, as a relatively inexpensive measure to minimize the risk of future slab or below-grade wall moisture problems from possible perched groundwater conditions or other potential moisture intrusion. The perimeter drain system should consist of a minimum 4-inch-diameter perforated PVC pipe, enveloped by 6 inches of drainage material on all sides. The drainage material should consist of a free-draining, well-graded sand and gravel, such as WSDOT Gravel Backfill for Walls - Section 9-03.12(4), with the additional criteria of containing less than 3 percent fines based on minus 3/4-inch fraction. All drainage pipes should be installed near the footing base level and should be sloped to drain away from the footings and hydraulically connected to a suitable discharge outlet point. Cleanouts should be installed for maintenance purposes. Roof and surface water runoff should not discharge into the perimeter drain system. Rather, these sources should discharge into separate tightline pipes and be routed away from the building to a storm drain or other appropriate location. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 19 19442-00 May 20, 2021 Final site grades should slope downward away from the building so that runoff water will flow to suitable collection points rather than ponding near the building. Ideally, the area surrounding the building should be capped with concrete, asphalt, or low-permeability (silty) soil to reduce surface water infiltration near the building. Asphalt Pavement Design and Subgrade Preparation A conventional asphaltic concrete pavement (ACP) design section typically consists of a hot mixed asphalt (HMA) layer over a crushed surfacing base course (CSBC), supported by a granular subbase course or properly prepared native/structural fill. Asphalt treated base course (ATB) may also be used in lieu of CSCB, to provide a more durable, temporary construction traffic surface, especially during wet weather conditions. An additional advantage of using ATB is to help identify weak subgrade areas (through visible cracking), prior to placement of the final asphalt surfacing layer. Assuming well-compacted, granular native soil or structural fill subgrade conditions, we typically recommend the standard asphalt pavement design sections shown in Table 5 for light-duty traffic (car parking), moderate-duty traffic (parking entryways and driveways), and heavy-duty traffic (HS-20 truck access driveways). Table 5 – Typical Asphalt Pavement Design Sections Pavement Course Layer Thickness (inches) Light-Duty Traffic Moderate-Duty Traffic Heavy-Duty Traffic Asphaltic concrete (AC) 2 3 4 Crushed surfacing base course (CSBC) 4 5 6 Asphalt treated base (ATB) Option a 3 3 4 Notes: a. In lieu of CSBC. The asphalt concrete pavement design sections listed in Table 5 (for a typical 20-year design life) assume a California bearing ratio value on the order of 10 to 15 percent, which is generally appropriate for densely compacted, granular soils. This assumes a firm and unyielding subgrade soil condition, prepared and proof rolled in accordance with the recommendations of our geotechnical report. Traffic conditions are assumed to consist of passenger cars in light-duty parking areas, cars to moderate truck traffic in moderate-duty parking entryways and driveways, and typical commercial HS-20 trucks in heavy-duty access driveways. The pavement thickness design sections listed in Table 5 are based on Traffic Index (TI) values ranging from about 4.0 (light duty section) to 6.0 (heavy duty section). WSDOT HMA Class 1/2 inch is typically suitable for the ACP course in car parking and private driveway areas. Crushed surfacing top course or base course should meet WSDOT Standard Specification 9-03.9(3). Recycled or pulverized concrete should generally not be used as CSBC for pavements. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 20 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 Pavement Subgrade Preparation Following site stripping, excavation, and backfilling, the exposed near-surface soil within all pavement subgrade areas should be compacted to at least 95 percent of the maximum dry density as determined by the modified Proctor test method (ASTM D1557), if warranted by soil moisture conditions. The subgrade should then be proof rolled with a loaded dump truck or heavy compactor to verify a firm and unyielding subgrade condition. Any localized zones of yielding subgrade disclosed during this proof rolling operation should be overexcavated to a maximum depth of 12 inches and replaced with a suitable structural fill material (granular subbase course). Alternately, a field evaluation of subgrade conditions may indicate a suitable geofabric may be used to stabilize the soft subgrade and minimize silt migration into the pavement section. Any structural fill within the upper 2 feet of the subgrade level should be compacted to at least 95 percent of the modified Proctor maximum dry density (ASTM D1557); fill material below this 2-foot depth should be compacted to at least 90 percent. We recommend a Hart Crowser representative verify the condition of the subgrade, structural fill, granular subbase, and crushed rock base course before each successive layer is placed. Stormwater Infiltration Considerations Because of the relatively shallow groundwater table (2 to 5 feet bgs), we do not recommend on-site stormwater infiltration at this site. Structural Fill We recommend using structural fill beneath footings, slabs-on-grade, and pavement sections as well as backfill behind subsurface walls and above utility installations. The suitability of soil used for structural fill depends primarily on its grain-size distribution and moisture content when placed. As the fines content (soil fraction passing the U.S. No. 200 sieve) increases, soil becomes more sensitive to small changes in moisture. Soil containing more than approximately 5 percent fines (by weight) cannot be consistently compacted to a firm, relatively unyielding condition when the moisture content is more than 2 percent above or below optimum. Structural fill must also be free of organic matter and other debris. Generally, any fill material with moisture content at or near optimum can be compacted as structural fill, provided it is placed on a firm and relatively unyielding subgrade surface. However, for fill placement during wet-weather site work, we recommend using clean fill, which refers to soil that has a fines content of 5 percent or less (by weight) based on the soil fraction passing the U.S. No. 4 sieve. Clean fill should meet the requirements specified in the Imported Structural Fill subsection below. We make the following general recommendations regarding structural fill placement and compaction:  Place and compact all structural fill in lifts with a loose thickness no greater than 8 to 10 inches. If small, hand-operated compaction equipment is used to compact structural fill such as within 12 inches of utility pipes or other structures, the lifts should not exceed 4 to 6 inches in loose thickness, depending on the equipment used. The maximum particle size within the structural fill should be DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 21 19442-00 May 20, 2021 limited to two-thirds of the loose lift thickness, to allow full compaction of the soil surrounding the large particles.  Generally, compact structural fill to a minimum of 90 percent of the modified Proctor maximum dry density, as determined by the ASTM D 1557 test procedure. However, below footings, building slabs, and within the upper 2 feet below pavement sections, fill should be compacted to a minimum of 95 percent. Hand compaction equipment should be used within 2 feet of subsurface walls, to avoid overstressing the wall.  Control the moisture content of the fill to within 2 percent of the optimum moisture based on laboratory Proctor tests. The optimum moisture content corresponds to the maximum attainable Proctor dry density.  Perform a representative number of in-place density tests, to verify adequate compaction. In addition, each structural fill lift and the subgrade area below it, should be verified by a representative of Hart Crowser.  Place structural fill only on dense and relatively unyielding subgrade, as described in the Site Preparation and Grading section. If subgrade areas are wet, clean material with a gravel content (material coarser than a U.S. No. 4 sieve) of at least 30 to 35 percent may be needed to bridge moisture-sensitive subsoils. In certain cases, clean crushed rock or quarry spalls may be required to stabilize weak or wet subgrade soil. Use of On-Site Soil as Structural Fill The predominantly granular portion of the historical fill and upper native soil (silty sand/gravel) will likely be suitable for reuse as structural fill, provided it is properly moisture conditioned to near optimum conditions during compaction. However, some of the near-surface native soils are fine-grained (sandy/clayey silt), are highly moisture sensitive, and not considered suitable for reuse as structural fill. We recommend the excavated soil intended for reuse as structural fill be stockpiled separately and reviewed by the on-site geotechnical engineer or geologist for suitability. Such stockpiles should be protected with plastic sheeting to prevent them from becoming overly wet during rainy weather. Note that the silty fill soil is not considered suitable for use as free-draining material. Imported Structural Fill If required, imported structural fill should be well-graded sand with a low fines content, free of organic and unsuitable materials. Generally, imported structural fill for most applications should meet the requirements in WSDOT Gravel Borrow, Section 9-03.14(1), with the added requirement the fines content should not exceed 5 percent. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 22 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 Temporary Open Cuts All temporary soil cuts for site excavations that are more than 4-feet deep should be adequately shored or sloped back to prevent sloughing and collapse in accordance with Washington Department of Occupational Safety and Health (DOSH) guidelines. Generally, the DOSH regulations consider granular soils (i.e., sand, silty sand, and sandy silt) to be Soil Type C, requiring a cut slope inclination of 1.5H:1V, or flatter. Very stiff to hard cohesive soils (i.e., sandy/clayey silt or lean clay), with an unconfined compressive strength greater than 0.5 tons per square foot may generally be considered Soil Type B, which requires a cut slope inclination of 1H:1V or less steep. Dense to very dense (compact) glacial till may generally be considered Soil Type A, which may cut at a slope inclination of 3/4H:1V according to the DOSH regulations. However, appropriate temporary slope inclinations will ultimately depend on the actual soil and groundwater seepage conditions exposed in the cuts at the time of construction. It is the responsibility of the contractor to ensure that all excavations are properly sloped or braced for worker protection, in accordance with DOSH guidelines. Based on our explorations, most of the near-surface site soil should be considered DOSH Soil Type C. The cut slope inclination of the overall slope cannot be steeper than that allowed for the weakest soil type within the excavation depth. If groundwater seepage is encountered within the excavation slopes, the cut slope inclination may have to be flatter than 1.5H:1V. We make the following additional recommendations for temporary excavation slopes:  Protect the slope from erosion with plastic sheeting for the duration of the excavation to reduce the risk of surface erosion and raveling.  Limit the maximum duration of the open excavation to the shortest time period possible.  Place no surcharge loads (equipment, materials, etc.) within 10 feet of the top of the slope. If temporary sloping is not feasible because of site spatial or other constraints, the excavation should be supported by a shoring system in accordance with DOSH guidelines. RECOMMENDED ADDITIONAL GEOTECHNICAL SERVICES Recommendations discussed in this report should be reviewed and modified as needed during the final design stages of the project. We also recommend incorporating geotechnical construction observation into the construction plans. The following sections present our recommended post-report geotechnical engineering services specific to this project. Post-Report Design Services We recommend Hart Crowser review geotechnical aspects of the final design plans and specifications to confirm our recommendations were properly understood and implemented. We can be available to discuss these issues with the design team as the design develops and as needed. Specifically, we recommend the following additional, post-report design services: DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Pan Abode Redevelopment Site | 23 19442-00 May 20, 2021 Provide geotechnical engineering support to the civil/structural engineer during preparation of project plans and specifications; and Prepare geotechnical review letters, as needed, in response to geotechnical plan review comments by the reviewing municipal agency or as part of the permitting process. Construction Observation Services The future performance and integrity of the structural elements of the project will depend largely on proper construction procedures. Monitoring and testing by experienced geotechnical personnel should therefore be considered an integral part of the construction process. The purpose of our observations is to verify compliance with design concepts and recommendations, and to allow design changes or evaluation of appropriate construction methods in case subsurface conditions differ from those anticipated prior to the start of construction. Consequently, we recommend retaining Hart Crowser to provide the following construction support services: Review geotechnical-related construction submittals from the contractor to verify compliance with the construction plans and the recommendations of this report; Attend a pre-construction conference with the contractor to discuss important geotechnical-related construction issues; Observe installation of AC piles to confirm adequate construction procedures and embedment depth into bearing soil; Observe installation of aggregate piers to confirm adequate construction procedures, spacing, and embedment depth within the GI reinforcement zone; Observe all exposed footing, slab-on-grade floor, and pavement subgrades after completion of GI or stripping/excavation to confirm appropriate subgrade preparation methods and that suitable native soil conditions have been reached, where applicable; Observe installation of all subsurface drainage systems and free-draining backfill; Monitor the placement of and test the compaction of all structural fill to verify conformance with specifications; and Assist with any other geotechnical considerations that may arise during construction. \\haleyaldrich.com\share\sea_projects\Notebooks\1944200_Pan_Abode_Geo_Env\Deliverables\DRAFT Update to Geotech Report \Geotech Report Update - Pan Abode Redevelopment.docx DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Document Path: L:\Notebooks\1944200_Pan_Abode_Geo_Env\GIS\1944200-AA (VMap).mxd Date: 4/19/2019 User Name: ericlindquist0 2,00 0 4,00 01,00 0 Fe et Pro ject Lo cation Se attle WAS HINGTON Ore gon Idaho Canada So urces: Esri, HERE, Garmin, USGS, Interma p, INCREMENT P, NRCan , Esri Japan, METI, Esri China (H ong Kong), Esri Korea, Esri (Thailan d), NGCC, © OpenStreetMa p co ntribut ors, an d the GIS User Co mmunity N Note: Feature locations are approximate. Pan Abode Redevelopment Site Renton, Washington Vicinity Map 194 42-00 4/19 Figure1 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 B-1 B-2 B-5 B-4 B-3 HC-B1 (-5) (0) (5) (10) (15) (15 ) (0) (8) (12) (18)(16) (15) (16) HC-B2 N 0 100 200 Scale in Feet Figure 19442-00 05/21 Renton, Washington Pan Abode Redevelopment Site 2 Site and Exploration Plan (Development Option A)File: \\haleyaldrich.com\share\sea_projects\Notebooks\1944200_Pan_Abode_Geo_Env\CAD\1944200-001 (SPlan).dwg Layout:8.5x11 - V Date: 05-20-2021 Author: elindquistSources: Base map prepared from PDF drawing "Overall Site Plan" dated 5/10/2021 provided by Hensley Lamkin Rachel, Inc. Aerial image provided by Bing. HC-B1 B-1 Legend Approximate Top of Pile Bearing Layer Elevation (NAVD 88) Boring (Hart Crowser 2019) Boring with Monitoring Well (Hart Crowser 2019) Boring (Hart Crowser 1985) Property Boundary (0) HC-B2 Undocumented Monitoring Well DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 19442-00 May 20, 2021 APPENDIX A Field Exploration Methods and Analysis DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 19442-00 May 20, 2021 APPENDIX A Field Exploration Methods and Analysis This appendix documents the processes Hart Crowser used to determine the nature of the soil and groundwater conditions in the project site. Explorations and Their Locations Subsurface explorations for this project were two mud-rotary borings. The exploration logs in this appendix show our interpretation of the drilling, sampling, and testing data. The boring logs indicate specific depths where the soils change, although the actual change may be gradual between samples. In the field, we classified the samples taken from the boring explorations according to the methods on Figure A-1, Key to Exploration Logs; the legend on this figure explains the symbols and abbreviations used in the logs and tables. Figure 2 shows the location of the explorations, found by hand-taping or pacing from existing physical features, supplemented by collecting GPS location coordinates with a smartphone. The ground surface elevations at these locations were interpreted from elevations shown on available site maps. The location and elevation of the explorations is only as accurate as allowed by the measurement method used. Mud-Rotary Borings The two mud-rotary borings (HC-B1 and HC-B2) were drilled on March 11, 2019, to a maximum depth of approximately 41.0 feet bgs. The borings were completed by Holt Services under subcontract to Hart Crowser, using a mud-rotary truck drill rig. A geotechnical engineer or geologist from Hart Crowser continuously observed the drilling. Detailed field logs were prepared for each boring. Using the SPT, we obtained samples at depth intervals of 2.5 to 5 feet. The boring logs are presented on Figures A-2 through A-3 in this appendix. These logs describe the vertical sequence of soils and materials encountered, based primarily on the SPT sampling and supported by our subsequent laboratory examination and testing. SPT Procedures The SPT is an approximate measure of soil density and consistency. To be useful, the results must be used with engineering judgment in conjunction with other tests. The SPT (as described in ASTM D 1586) was used to obtain disturbed samples. This test employs a standard 2-inch outside-diameter split-spoon sampler. A 140-pound hammer free-falling 30 inches drives the sampler into the soil for 18 inches. The number of blows required to drive the sampler the last 12 inches only is the standard penetration resistance. This resistance, or blow count, measures the relative density of granular soils and the consistency of cohesive soils. The blow counts are plotted on the boring logs at their respective sample depths. Soil samples are recovered from the split-barrel sampler, field classified, placed into watertight jars, and taken to Hart Crowser’s laboratory for further testing, as described in Appendix B. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 A-2 | Pan Abode Redevelopment Site 19442-00 May 20, 2021 When very dense materials preclude driving the total 18-inch sample, the penetration resistance is entered on the logs as follows: Penetration less than 6 inches. The log indicates the total number of blows over the number of inches of penetration. Penetration greater than 6 inches. The blow count noted on the log is the sum of the total number of blows completed after the first 6 inches of penetration. This sum is expressed over the number of inches driven that exceed the first 6 inches. The number of blows needed to drive the first 6 inches is not reported. For example, a blow count series of 12 blows for 6 inches, 30 blows for 6 inches, and 50 (the maximum number of blows counted within a 6-inch increment for SPT) for 3 inches would be recorded as 80/9. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 Figure A-1Project: Location: Project No.: Pan Abode Redevelopment Renton, WA 19442-00 Key to Exploration Logs Sheet 1 of 1 Organic Soil; Organic Soil with Sand or Gravel; Sandy or Gravelly Organic SoilOL/OH CH Fat Clay; Fat Clay with Sand or Gravel; Sandy or Gravelly Fat Clay Lean Clay; Lean Clay with Sand or Gravel; Sandy or Gravelly Lean ClayCL Clays Organics Highly Organic (>50% organic material) (based on Atterberg Limits) Silty Clay Silty Clay; Silty Clay with Sand or Gravel; Gravelly or Sandy Silty Clay Sand, Gravel Trace Few Cobbles, Boulders Trace Few Little Some Minor Constituents <5 5 - 15 <5 5 - 10 15 - 25 30 - 45 Liquid Limit (LL) Water Content (WC) Plastic Limit (PL)Moisture Dry Moist Wet Absence of moisture, dusty, dry to the touch Damp but no visible water Visible free water, usually soil is below water table Cuttings 0 5 11 31 Very loose Loose Medium dense Dense Very dense to to to to to >30 to to to to >50 4 10 30 50 Very soft Soft Medium stiff Stiff Very stiff Hard 0 2 5 9 16 1 4 8 15 30 Well Symbols Sample Description Relative Density/Consistency Soil density/consistency in borings is related primarily to the standard penetration resistance (N). Soil density/consistency in test pits and probes is estimated based on visual observation and is presented parenthetically on the logs. N (Blows/Foot) SILT or CLAY Consistency SAND or GRAVEL Relative Density N (Blows/Foot) Slough Estimated Percentage Well Tip or Slotted Screen Clean Gravels Gravels Sands with few Fines Sands Sands with Fines (>12% fines) 1.5" I.D. Split Spoon Core Run Groundwater Indicators Soil Test Symbols Sonic Core Thin-walled SamplerModified California Sampler Grab Sample Symbols Groundwater Level on Date or At Time of Drilling (ATD) Groundwater Level on Date Measured in Piezometer Groundwater Seepage (Test Pits) Identification of soils in this report is based on visual field and laboratory observations which include density/consistency, moisture condition, grain size, and plasticity estimates and should not be construed to imply field nor laboratory testing unless presented herein. ASTM D 2488 visual-manual identification methods were used as a guide. Where laboratory testing confirmed visual-manual identifications, then ASTM D 2487 was used to classify the soils. Gravels with Fines Elastic Silt; Elastic Silt with Sand or Gravel; Sandy or Gravelly Elastic Silt (5-12% fines) (>12% fines) Poorly Graded Gravel with Clay; Poorly Graded Gravel with Clay and Sand Graph GW-GM Symbols GW GW-GC GC SW SP SW-SM SW-SC SP-SM SP-SC SM SC ML MH (<5% fines) Poorly Graded Sand with Clay; Poorly Graded Sand with Clay and Gravel Typical Descriptions Well-Graded Gravel; Well-Graded Gravel with Sand Poorly Graded Gravel; Poorly Graded Gravel with Sand Clayey Gravel; Clayey Gravel with Sand %F AL CA CAUC CAUE CBR CIDC CIUC CK0DC CK0DSS CK0UC CK0UE CRSCN DSS DT GS HYD ILCN K0CN kc kf MD OC OT P PID PP SG TRS TV UC UUC VS WC Percent Passing No. 200 Sieve Atterberg Limits (%) Chemical Analysis Consolidated Anisotropic Undrained Compression Consolidated Anisotropic Undrained Extension California Bearing Ratio Consolidated Drained Isotropic Triaxial Compression Consolidated Isotropic Undrained Compression Consolidated Drained k0 Triaxial Compression Consolidated k0 Undrained Direct Simple Shear Consolidated k0 Undrained Compression Consolidated k0 Undrained Extension Constant Rate of Strain Consolidation Direct Simple Shear In Situ Density Grain Size Classification Hydrometer Incremental Load Consolidation k0 Consolidation Constant Head Permeability Falling Head Permeability Moisture Density Relationship Organic Content Tests by Others Pressuremeter Photoionization Detector Reading Pocket Penetrometer Specific Gravity Torsional Ring Shear Torvane Unconfined Compression Unconsolidated Undrained Triaxial Compression Vane Shear Water Content (%) Sand Pack Monument Surface Seal Bentonite Seal Well Casing Well-Graded Sand; Well-Graded Sand with Gravel Poorly Graded Sand; Poorly Graded Sand with Gravel Silty Sand; Silty Sand with Gravel Silty Gravel; Silty Gravel with Sand PT CL-ML Clayey Sand; Clayey Sand with Gravel Silt; Silt with Sand or Gravel; Sandy or Gravelly Silt Fine Grained Soils More than 50% of Material Passing No. 200 Sieve Silts Well-Graded Gravel with Silt; Well-Graded Gravel with Silt and Sand Well-Graded Gravel with Clay; Well-Graded Gravel with Clay and Sand Poorly Graded Gravel with Silt; Poorly Graded Gravel with Silt and Sand Sand and Sandy Soils More than 50% of Coarse Fraction Passing No. 4 Sieve Gravel and Gravelly Soils More than 50% of Coarse Fraction Retained on No. 4 Sieve Coarse Grained Soils More than 50% of Material Retained on No. 200 Sieve GP GP-GM GP-GC GM Major Divisions Well-Graded Sand with Silt Well-Graded Sand with Silt and Gravel (<5% fines) Well-Graded Sand with Clay; Well-Graded Sand with Clay and Gravel Poorly Graded Sand with Silt; Poorly Graded Sand with Silt and Gravel (5-12% fines) USCS USCS Soil Classification Chart (ASTM D 2487) Peat - Decomposing Vegetation - Fibrous to Amorphous Texture 3.25" O.D. Split Spoon Signal Cable Vibrating Wire Piezometer (VP)KEY TO EXP LOGS (SOIL ONLY) - J:\GINT\HC_LIBRARY.GLB - 3/26/19 13:29 - L:\NOTEBOOKS\1944200_PAN_ABODE_GEO_ENV\FIELD DATA\PERM_GINT FILES\1944200-BL.GPJ - kzlDocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 S-1 PID, WC, No odor, no sheen S-2 PID, WC, No odor, no sheen S-3 GS, PID, WC, No odor, no sheen S-4 PID, No odor, no sheen S-5 PID, No odor, no sheen S-6A PID, No odor, no sheen S-6B S-7 GS, PID, WC, No odor, no sheen S-8 PID, No odor, no sheen S-9 PID, No odor, no sheen S-10 PID, No odor, no sheen 18in. 18in. 18in. 1in. 7in. 0in. 18in. 12in. 3in. 6in.1 2 11 0 6 5 7 8 7 1 2 1 11 12 17 3 2 1 12 10 7 24 14 14 50 30 50 2 inches of asphalt concrete pavement. [FILL] SILTY SAND to SILTY SAND WITH GRAVEL (SM), medium dense to very loose, wet, gray-brown to gray, medium to coarse grained sand and subangular gravel. SILTY GRAVEL WITH SAND (GM), medium dense, gray, wet, coarse sand, subangular gravel and sand. SILT WITH SAND (ML), soft, gray, moist. SILTY SAND WITH GRAVEL to POORLY GRADED SAND WITH GRAVEL (SM/SP), medium dense, wet to moist, medium grained sand and angular gravel. SILTY GRAVEL WITH SAND (GM), very dense, gray, moist, medium grained sand, angular gravel. Bottom of Borehole at 41.0 feet. Sample Data HC-B1 Boring Log Date Started:3/11/19 Logged by:N. Jones Drilling Method:Mud Rotary Hammer Type:Auto-hammer Total Depth:41 feet Rig Model/Type:Mobile B-59 / Truck-mounted drill rig Drilling Contractor/Crew:Holt Services, Inc. / Kevin 10 20 30 40 Hammer Drop Height (inches):30Hammer Weight (pounds):140 WC (%) Hole Diameter:5.875 inches Measured Hammer Efficiency (%): NAVertical Datum:NAVD 88 Horizontal Datum:WGS 84 Ground Surface Elevation: 30.3 feet Depth to Groundwater:Not Identified Location and ground surface elevations are approximate.Comments: Location:Lat: 47.531260 Long: -122.199350 Checked by:T. Remund Date Completed:3/11/19 Casing Diameter:NA Sheet 1 of 1 Figure A-2Project: Location: Project No.: Pan Abode Redevelopment Renton, WA 19442-00 General Notes: 1. Refer to Figure A-1 for explanation of descriptions and symbols. 2. Material descriptions and stratum lines are interpretive and actual changes may be gradual. Solid stratum lines indicate distinct contact between material strata or geologic units. Dashed stratum lines indicate gradual or approximate change between material strata or geologic units. 3. USCS designations are based on visual-manual identification (ASTM D 2488) unless otherwise supported by laboratory testing (ASTM D 2487). 4. Groundwater level, if indicated, is at time of drilling/excavation (ATD) or for date specified. Level may vary with time.Depth (feet)Elevation (feet)Depth (feet)Length (inches)PID Graphic LogNumber TestsRecoveryTypeBlow Count SPT N Value Material Description Fines Content (%)HC BORING LOG - J:\GINT\HC_LIBRARY.GLB - 4/19/19 11:50 - L:\NOTEBOOKS\1944200_PAN_ABODE_GEO_ENV\FIELD DATA\PERM_GINT FILES\1944200-BL.GPJ - kzl18 18 18 18 18 18 18 18 4 12 0 5 10 15 20 25 30 35 40302520151050-5-100 5 10 15 20 25 30 35 40 13 11 15 3 29 3 17 28 50/1st 4" 50/5.5" 10 23 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 S-1 GS, PID, WC, No odor, no sheen S-2 PID, No odor, no sheen S-3 PID, No odor, no sheen S-4 PID, No odor, no sheen S-5 PID, No odor, no sheen S-6 GS, PID, WC, No odor, no sheen S-7 PID, No odor, no sheen S-8 S-9 6in. 6in. 8in. 10in. 18in. 18in. 13in. 18in. 9in.4 2 4 1 2 1 10 12 11 7 10 9 6 7 7 2 2 4 20 16 23 21 24 25 27 50 3 inches of asphalt concrete pavement. SILTY SAND WITH GRAVEL (SM), loose to very loose, wet, brown, medium grained sand with subrounded gravel. SILTY SAND WITH GRAVEL to SILTY GRAVEL WITH SAND (SM/GM), medium dense, wet, gray, coarse grained sand with subangular gravel and sand. SANDY SILT (ML), medium stiff, gray, wet, fine grained sand. SILTY SAND WITH GRAVEL to POORLY GRADED SAND WITH GRAVEL (SM/SP), dense, wet, gray, medium grained sand and angular gravel. Becomes less silty; increased gravel content. SILTY GRAVEL WITH SAND (GM), very dense, gray, moist, angular gravel. Bottom of Borehole at 36.0 feet. ATD 3/25/2019Sample Data HC-B2 Boring Log Date Started:3/11/19 Logged by:N. Jones Drilling Method:Mud Rotary Hammer Type:Auto-hammer Total Depth:36 feet Rig Model/Type:Mobile B-59 / Truck-mounted drill rig Drilling Contractor/Crew:Holt Services, Inc. / Kevin 10 20 30 40 Hammer Drop Height (inches):30Hammer Weight (pounds):140 WC (%) Hole Diameter:5.875 inches Measured Hammer Efficiency (%): NAVertical Datum:NAVD 88 Horizontal Datum:WGS 84 Ground Surface Elevation: 32.5 feet Depth to Groundwater:2.25 feet Well Tag ID: BLK-951 Location and ground surface elevations are approximate. Comments: Location:Lat: 47.530770 Long: -122.198710 Checked by:T. Remund Date Completed:3/11/19 Casing Diameter: Sheet 1 of 1 Figure A-3Project: Location: Project No.: Pan Abode Redevelopment Renton, WA 19442-00 General Notes: 1. Refer to Figure A-1 for explanation of descriptions and symbols. 2. Material descriptions and stratum lines are interpretive and actual changes may be gradual. Solid stratum lines indicate distinct contact between material strata or geologic units. Dashed stratum lines indicate gradual or approximate change between material strata or geologic units. 3. USCS designations are based on visual-manual identification (ASTM D 2488) unless otherwise supported by laboratory testing (ASTM D 2487). 4. Groundwater level, if indicated, is at time of drilling/excavation (ATD) or for date specified. Level may vary with time.Depth (feet)Elevation (feet)Depth (feet)Length (inches)PID Graphic LogNumber TestsRecoveryTypeBlow Count SPT N Value Material Description Fines Content (%)HC BORING LOG - J:\GINT\HC_LIBRARY.GLB - 4/19/19 11:50 - L:\NOTEBOOKS\1944200_PAN_ABODE_GEO_ENV\FIELD DATA\PERM_GINT FILES\1944200-BL.GPJ - kzlWater LevelWell Construction18 18 18 18 18 18 18 18 11 0 5 10 15 20 25 30 35 40302520151050-5-100 5 10 15 20 25 30 35 40 6 3 23 19 14 6 39 49 50/5" 16 62 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 19442-00 May 20, 2021 APPENDIX B Soil Laboratory Testing DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 19442-00 May 20, 2021 APPENDIX B Soil Laboratory Testing Laboratory tests were performed for this study to evaluate the basic index and geotechnical engineering properties of the site soils. Disturbed samples from the boring SPT split spoons were tested. The tests performed and the procedures followed are outlined below. A summary of the test results is included on Table B-1. Soil Classification Soil samples from the explorations were visually classified in the field and then taken to our laboratory, where the classifications were verified in a relatively controlled laboratory environment. The classifications of selected samples were checked by laboratory tests such as Atterberg limits determinations and grain size analyses. Visual classifications were made in general accordance with ASTM Test Method D 2488, as presented on Figure A-1 in Appendix A. ASTM Test Method D 2487 was used to classify soils based on laboratory test results. Water Content Determination Water content was determined on a representative number of samples recovered in the explorations, in general accordance with ASTM Test Method D 2216, as soon as possible following their arrival in our laboratory. In addition, water content is routinely determined for samples subjected to other testing. The results of the water content tests are summarized in Table B-1 and plotted at the respective sample depths on the exploration logs in Appendix A. Grain Size Analysis Grain size analysis tests were performed to determine the quantitative distribution of particle sizes within representative samples. The tests were performed in general accordance with ASTM Test Method D 6913 and D 1140. The “percent fines” portion of the test results are indicated on the exploration logs in Appendix A, and the full test results are plotted as percent finer by weight vs grain size on Figure B-2. Percent Fines Fines content tests were performed on selected samples to determine the percentage of particles finer than the U.S. No. 200 sieve (silt and clay). The tests were performed in general accordance with ASTM Test Method D 1140. The percent fines test results are summarized in Table B-1 and indicated on the exploration logs included in Appendix A. DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 HC-B1 S-1 2.5 29.5 HC-B1 S-2 5.0 29.2 HC-B1 S-3 7.5 38.0 51.8 10.1 13.0 SP-SM POORLY GRADED SAND WITH SILT AND GRAVEL HC-B1 S-4 10.0 HC-B1 S-5 15.0 HC-B1 S-6A 20.0 HC-B1 S-6B 21.5 HC-B1 S-7 25.0 4.7 72.2 23.1 17.4 SM SILTY SAND HC-B1 S-8 30.0 HC-B1 S-9 35.0 HC-B1 S-10 40.0 HC-B2 S-1 2.5 48.9 35.2 15.9 20.6 GM SILTY GRAVEL WITH SAND HC-B2 S-2 5.0 HC-B2 S-3 7.5 HC-B2 S-4 10.0 HC-B2 S-5 15.0 HC-B2 S-6 20.0 1.0 37.4 61.6 23.1 CL SANDY LEAN CLAY HC-B2 S-7 25.0 HC-B2 S-8 30.0 HC-B2 S-9 35.0 TABLE B-1: SUMMARY OF LABORATORY RESULTS USCS Group Symbol Soil DescriptionLiquid Limit Plastic Limit Water Content (%) Borehole DepthSample ID % Fines% Sand% Gravel PROJECT LOCATION Renton, WAPROJECT NUMBER 1944200 PROJECT NAME Pan Abode Redevelopment SELECT SUMMARY WITH DESC MOD01 - GINT STD US LAB.GDT - 3/27/19 16:49 - L:\NOTEBOOKS\1944200_PAN_ABODE_GEO_ENV\FIELD DATA\PERM_GINT FILES\1944200-BL.GPJDocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 0.0010.010.1110100 #200#140#100#60#30#40#20#10#4PERCENT FINER321-1/23/41/23/861Particle-Size Analysis % Sand D30LL PI D85 D60 D50 4.002 0.281 16.916 1.515 0.219 2.472 0.330 0.112 0.191 0.152 0.37 D15 D10 Cc Cu 54.45 GRAIN SIZE - mm % Silt % Clay 38.0 4.7 48.9 1.0 % Gravel 0.0 0.0 0.0 0.0 % Cobbles Remarks: 13 17 21 23 USCSMC% 51.8 72.2 35.2 37.4 11.170 0.729 26.229 0.179 10.1 23.1 15.9 61.6 SP-SM SM GM ML/CL U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS HYDROMETER Sheet 1 of 1 Figure B-2 Source: HC-B1 Source: HC-B1 Source: HC-B2 Source: HC-B2 Sample No.: S-3 Sample No.: S-7 Sample No.: S-1 Sample No.: S-6 Depth: 7.5 to 9.0 Depth: 25.0 to 26.5 Depth: 2.5 to 4.0 Depth: 20.0 to 21.5 Location and Description Composited with S-2 Classification based on grain size results and visual manual method. Project: Location: Project No.: Pan Abode Redevelopment Renton, WA 19442-00 POORLY GRADED SAND WITH SILT AND GRAVEL SILTY SAND SILTY GRAVEL WITH SAND SANDY SILT TO SANDY LEAN CLAY coarseCOBBLESGRAVEL finemediumfinecoarse SAND SILT OR CLAY HC GRAIN SIZE - J:\GINT\HC_LIBRARY.GLB - 4/19/19 14:47 - L:\NOTEBOOKS\1944200_PAN_ABODE_GEO_ENV\FIELD DATA\PERM_GINT FILES\1944200-BL.GPJ - hclabDocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 19442-00 May 20, 2021 APPENDIX C Historical Explorations DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764 DocuSign Envelope ID: 333EED88-7BF3-460B-A1D8-61BB96A24764