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Home My WebLink AboutEX_06_RS_Geotechnical_Report_181119_v1GEOTECHNICAL ENGINEERING REPORT Proposed 38th Street Short Plat 1825 NE 38th Street Renton, Washington Project No. 2002.01 October 12, 2018 Prepared for: KP Development Prepared by: RECEIVED 01/19/2022 JDing PLANNING DIVISION DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 19019 36th Avenue West, Suite E Lynnwood, WA 98036 (425) 582-9928 Project No. 2002.01 October 12, 2018 KP Development 331 NW 78th Street Seattle, WA 98117 Attention: Mr. Cameron Damsko Subject: Geotechnical Engineering Report Proposed 38th Street Short Plat 1825 NE 38th Street Renton, Washington Dear Damsko, In accordance with your request and written authorization, Zipper Geo Associates, LLC (ZGA) has completed the subsurface explorations and geotechnical engineering report for the proposed 38th Street Short Plat project. This report presents the findings of the subsurface exploration and geotechnical recommendations for the project. Our work was completed in general accordance with our Proposal for Geotechnical Services (Proposal No. P18182) dated April 17th, 2018. Written authorization to proceed was provided you on April 17th, 2018. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us. Sincerely, Zipper Geo Associates, LLC Robert A. Ross, P.E. Principal Geotechnical Engineer Copies: Addressee (1) 10/25/18 DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 TABLE OF CONTENTS Page INTRODUCTION ........................................................................................................................................... 1 PROJECT UNDERSTANDING..................................................................................................................... 1 SURFACE CONDITIONS ............................................................................................................................. 2 SUBSURFACE CONDITIONS...................................................................................................................... 2 Soil Conditions ................................................................................................................................................. 2 Groundwater Conditions ................................................................................................................................. 3 Summary of Laboratory Testing ...................................................................................................................... 3 CONCLUSIONS AND RECOMMENDATIONS ............................................................................................ 3 General .......................................................................................................................................................... 3 Geologically Hazardous Ares ........................................................................................................................... 4 Seismic Design Considerations ........................................................................................................................ 5 Site Preparation ............................................................................................................................................... 5 Structural Fill Materials and Preparation ........................................................................................................ 6 Underground Utilities ...................................................................................................................................... 8 Temporary and Permanent Slopes .................................................................................................................. 9 Building Foundations ..................................................................................................................................... 10 Permanent Foundation Retaining Walls........................................................................................................ 12 Site Retaining Walls ....................................................................................................................................... 13 Rockeries ....................................................................................................................................................... 13 MSE and Gravity Block Walls ........................................................................................................................ 13 Stormwater Infiltration Feasibility ................................................................................................................ 14 Stormwater Detention Vault ......................................................................................................................... 14 On-Grade Concrete Slabs .............................................................................................................................. 14 Permanent Drainage Considerations ............................................................................................................ 15 CLOSURE ................................................................................................................................................... 15 FIGURES Figure 1 – Site and Exploration Plan APPENDICES Appendix A – Subsurface Exploration Procedures and Logs Appendix B – Laboratory Testing Procedures and Results DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Page 1 GEOTECHNICAL ENGINEERING REPORT PROPOSED 38th Street Short Plat 1825 NE 38th Street RENTON, WASHINGTON Project No. 2002.01 October 12th, 2018 INTRODUCTION This report documents the surface and subsurface conditions encountered at the site and our geotechnical engineering recommendations for the proposed 38th Street Short Plat project. Our geotechnical engineering scope of services for the project included a literature review, site reconnaissance, subsurface exploration, laboratory testing, geotechnical engineering analysis, and preparation of this report. The observations and conclusions summarized herein are based in part upon conditions observed in our subsurface explorations and site observations. In the event that site conditions change, it may be necessary to modify the conclusions and recommendations presented in this report. This report is an instrument of service and has been prepared in general accordance with locally accepted geotechnical engineering practice. This report has been prepared for the exclusive use of KP Development, and its agents, for specific application to the subject property and stated purpose. PROJECT UNDERSTANDING Based on our review of preliminary civil engineering plans prepared by Preferred Engineering, LLC, we understand the project will consist of an 8 lot residential development on a 1.44 acre site located at 1825 NE 38th Street in Renton, Washington. Mass grading for the project is excepted to include fills in the western portion of the property and cuts in the eastern portion of the property. Maximum fill depths are expected to be about 6 feet, and maximum cut depths are expected to be about 20 feet. Some of the cuts and fills outside the proposed house locations will be supported by site retaining walls. Site fill walls are expected to have a maximum anticipated exposed height of about 6 feet, and cut walls are expected to have a maximum exposed height of about 14 feet. The new houses will require foundation retaining walls, and we expect the maximum exposed height of these walls will be about 16 feet. The project will include construction of underground utilities including a stormwater detention vault located in the NE 38th Street right-of-way north of the proposed houses, and other typical service utilities including power, water, sewer, and gas. Some of these utilities including the stormwater detention vault and sanitary sewer will require substantial temporary excavations on the order of 20 to 25 feet below site grade for installation. The project will also include improvements to the NE 38th Street and Lincoln Avenue NE rights-of-way. Existing topography and a generalized plan view of the proposed site improvements are shown on the attached Figure 1, Site and Exploration Plan. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 2 SURFACE CONDITIONS The project site consists of two parcels totaling about 1.44 acres of land located at 1825 NE 38th Street in Renton, Washington . A portion of the site is currently developed with an existing single-family home. The site is bordered to the north and south by developed residential property; to the east by Lincoln Avenue NE; and to the west by an undeveloped, forested slope. Topographically, the site generally occurs as a west to northwest-facing hill side. From Lincoln Avenue NE, the site generally slopes moderately downward to the west to the top of a steep slope that borders the west property boundary. The maximum total vertical relief of the property occurs between the southeast and northwest property boundaries and is about 58 feet. Beyond the west property boundary, the ground surface generally slopes steeply downward to the northwest. Vegetation on the site generally consists of dense deciduous and coniferous trees and brush, and areas of ornamental landscaping. No springs or groundwater seepage were observed on the property at the time our subsurface explorations were completed. The site, along with the proposed short plat layout are shown on the attached Site and Exploration Plan, Figure 1. SUBSURFACE CONDITIONS Mapped Geology We reviewed published geologic mapping of the site vicinity through the Washington State Department of Natural Resource’s web-based mapping application Washington Geologic Information Portal https://geologyportal.dnr.wa.gov/). The published mapping indicates the site is underlain by Vashon Till. The mapping describes Vashon Till as a nonsorted mixture of clay, silt, sand, pebbles, cobbles, and boulders, all in variable amounts. The mapping further describes the Till as “ It typically is hard lodgement till and often is referred to as "hardpan." The "hardpan" is largely a result of compaction caused by the great weight of the overriding ice, hundreds of meters thick.” Soil Conditions Soil conditions at the site were evaluated through the completion of 2 geotechnical test borings (B-1 to B- 2). The borings were advanced to a depth of about 41.5 feet below existing site grades. The approximate boring locations are shown on the attached Site and Exploration Plan, Figure 1. Soils were visually classified in general accordance with the Unified Soil Classification System. Descriptive logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are presented in Appendix A. A generalized description of soil conditions encountered in the borings is presented below. Detailed descriptions of soils encountered are provided on the descriptive logs in Appendix A. Surficial soils conditions observed in the borings generally consisted of about 6 to 8 inches of forest duff and topsoil. Below the forest duff and topsoil, soil conditions observed in borings generally consisted of about 7 to 10 feet of loose to medium dense sand and silt. Below the loose to medium dense sand and silt, soil conditions observed in the borings generally consisted of medium dense to very dense sand and very stiff to DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 3 hard silt to the completion depths of about 41.5 feet below existing site grade. The medium dense to very dense sand and very stiff to hard silts observed in the borings is interpreted to be glacial till. It should be noted that our exploration logs describe soil conditions encountered at specific locations on the site. Subsurface soil and groundwater conditions at other areas of the site may differ from those encountered in our explorations. If variations become apparent during construction, the recommendations in this report may need to be modified. Groundwater Conditions Indications of perched groundwater such as soil iron oxide staining and wet to saturated soil conditions were observed in both borings. Indications of perched groundwater were observed at a depth of about 15 feet in both borings. Perched groundwater typical consists of a thin saturated soil zone the develops between upper, weathered soils and lower unweathered glacial till soils. The thickness of the saturated zone varies, and is typically thicker in wetter months of the year. Fluctuations in groundwater levels will likely occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the explorations were performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher than indicated on the logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project. Summary of Laboratory Testing Laboratory testing was completed on select soil samples obtained from the explorations. Moisture content testing of soil samples obtained within the upper 15 feet of existing site grade ranged from about 6 to 32 percent with an average of about 18 percent. CONCLUSIONS AND RECOMMENDATIONS General Based on our subsurface exploration program and associated research, we conclude that the proposed development is feasible from a geotechnical standpoint, contingent on proper design and construction practices and implementation of the recommendations presented in this report. Our recommendations are presented in the following sections. The recommendations contained in this report are based upon the results of field and laboratory testing which are presented in Appendices A and B), engineering analyses, and our current understanding of the proposed project. ASTM and Washington State Department of Transportation (WSDOT) specification codes cited herein respectively refer to the current manual published by the American Society for Testing Materials and the current edition of the WSDOT Standard Specifications for Road, Bridge, and Municipal Construction, (M41-10). DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 4 Geologically Hazardous Ares As part of our services, we evaluated the presence of regulated geologically hazardous areas (GHAs) at the site. Title IV, Chapter 3 of the Renton Municipal Code (the Code) designates GHAs as Steep Slopes, Landslide Hazards, Erosion Hazards, Seismic Hazards, and Coal Mine Hazards. The reader is referred to the Code for definitions of individual GHAs. The NRCS Web Soil Survey maps a majority of the site as Alderwood Gravelly Sandy Loam, 15 to 30 percent slopes. The steep slope located west of the property is mapped as Alderwood and Kitsap soils, very steep. The area mapped as Alderwood and Kitsap soils, very steep will not be disturbed as part of this project. Based on the NRCS mapping, the site meets the Code definition of a High Erosion Hazard. For mitigation of erosion hazards at the site, we recommend the following: A proper temporary erosion and sediment control plan should be prepared in accordance with local standards by the project civil engineer. All areas disturbed by construction and not permanently covered with hard surfaces should be adequately stabilized through permanent landscaping. Weekly on-site inspections by a Certified Erosion and Sediment Control Lead (CESCL) should be completed. Design and construct the project in accordance with the recommendations presented in this report. Based on definitions in the Code, areas of the site meet the criteria for Sensitive Slopes, Protected Slopes, and Low to High Landslide Hazards. The steep slope that borders the west property line of the site meets the Code definition of a Protected Slope (PS) and High Landslide Hazard Area (HLHA). The limits of this Protected Slope/High Landslide Hazard Area are shown on the attached Figure 1. For PSs and HLHAs, the Code requires a buffer be recommended by the geotechnical engineer and a 15 foot structure setback beyond the buffer. Based on soil conditions observed in our borings, it is our opinion a 25 foot buffer is adequate. Site slopes east of the steep western slope generally meet the Code definitions for Sensitive Slopes and Medium Landslide Hazards. Grading for the project will completely alter these slopes. Based on our review of the preliminary grading plan, the graded slopes will not meet the criteria for PSs or HLHAs. It is our opinion that no buffer or building setback from the post-development slopes is necessary provided earthwork for the project is completed in accordance with the recommendations presented in this report. Based on soil conditions observed in our explorations, it is our opinion the site does not meet the Code definition for a Seismic Hazard Area. Additionally, there are no known mapped coal workings below the site, and therefore, the site does not meet the Code definition for a Coal Mine Hazard Area. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 5 Provided that the above-recommended mitigation measures are implemented, it is our opinion that the proposal will not increase the threat of the geological hazards to adjacent or abutting properties beyond pre-development conditions, will not adversely impact other critical areas, and the development can be safely accommodated on the site. Seismic Design Considerations The City of Renton adopts the 2015 edition of the International Residential Code with amendments for design of residential structures. Per Section 4-5-055 of the Code, the City requires residential structures to be designed assuming Seismic Design Category D2. Site Preparation Erosion Control Measures: Stripped surfaces and soil stockpiles are typically a source of runoff sediments. We recommend that silt fences, berms, and/or swales be installed around the downslope side of stripped areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet weather, we recommend that all stripped surfaces be covered with straw to reduce runoff erosion, whereas soil stockpiles should be protected with anchored plastic sheeting. Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a manner and sequence that will provide drainage at all times and provide proper control of erosion. The site should be graded to prevent water from ponding in construction areas and/or flowing into and/or over excavations. Exposed grades should be crowned, sloped, and smooth-drum rolled at the end of each day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from subgrades and work areas immediately and prior to performing further work in the area. Equipment access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely manner. Clearing and stripping: Once TESC measures are installed, we expect site preparation to continue with demolition of existing structures on the site, clearing and grubbing brush and trees, and stripping of organic rich topsoil. We recommend all elements of existing structures on the site be demolished and wasted off site. We recommend all tree stumps and roots larger than ½ inch in diameter be cleared and grubbed from the areas planned for improvement. Based on our explorations, stripping depths to remove topsoil is estimated to range from about 6 to 8 inches. Stripping depths may be greater near trees and brush to fully remove root systems. All clearing and stripping debris should be wasted off site or, if approved, used for topsoil in landscape areas. Subgrade Preparation: Once site preparation is complete, all areas that are at design subgrade elevation or areas that will receive new structural fill should be moisture conditioned to a moisture content within plus or minus two percent of optimum moisture content for compaction. The subgrade should then be compacted to a firm and unyielding condition. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 6 In areas of the site that will be filled, existing shallow subsurface soils contain a considerable fraction of silt and appear above optimum moisture content for compaction. As such, it appears that moisture conditioning consisting of windrowing and drying site soils will be required in order to achieve an adequate moisture content for compaction. Moisture conditioning of site soils will only be feasible during dry weather. Therefore, we recommend earth work be completed during the summer months. During wet weather, achieving a moisture content adequate for compaction will be impossible. If earthwork or construction activities take place during extended periods of wet weather, or if the in situ moisture conditions are elevated above the optimum moisture content, the soils will become unstable and not compactable. In the event the exposed subgrade becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend that the materials be removed to a sufficient depth in order to develop stable subgrade soils that can be compacted to the minimum recommended levels. Alternatively, wet subgrades could be chemically treated with cement or kiln dust. Once compacted, subgrades should be evaluated through density testing and proof rolling with a loaded dump truck or heavy rubber-tired construction equipment weighing at least 20 tons to assess the subgrade adequacy and to detect soft and/or yielding soils. Freezing Conditions: If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. Structural Fill Materials and Preparation Structural fill includes any material placed below foundations and pavement sections, within utility trenches, to construct embankments, and behind retaining walls. Prior to the placement of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site Preparation section of this report. Laboratory Testing: Representative samples of on-site and imported soils to be used as structural fill should be submitted for laboratory testing at least 4 days in advance of its intended use in order to complete the necessary Proctor tests. Reuse of Site Soils as Structural Fill: The suitability for reuse of site soils as structural fill depends on the composition and moisture content of the soil. Soils encountered in excavations at the site are expected to consist of sands and silts with a significant fines content (15 to over 30 percent). As the amount of fines increases, the soil becomes increasingly sensitive to small changes in moisture content. Soils containing more than about 5 percent fines cannot be consistently compacted to the appropriate levels when the moisture content is more than approximately 2 percent above or below the optimum moisture content DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 7 per ASTM D1557). Optimum moisture content is that moisture content which results in the greatest compacted dry density with a specified compactive effort. Laboratory testing of select soil samples indicates the in-place moisture content of site soils ranges from about 6 to 32 percent with an average of about 18 percent. Optimum moisture content of site soils is estimated to be about 6 to 10 percent. Therefore, on average, site soils appear to be significantly above optimum moisture content for compaction. The project team and bidding contractors should assume that drying of site soils will be required to achieve an adequate moisture content for compaction. Alternatively, cement treatment of site soils to be reused as structural fill could be considered. Drying of site soils during wet weather will be impossible. During wet weather, the project team and bidding contractors should expect that site soils will not be suitable for reuse as structural fill unless cement treated. Alternatively, during wet weather, imported soils with little to no fines could be considered. We recommend that site soils used as structural fill have less than 4 percent organics by weight and have no woody debris greater than ½ inch in diameter. We recommend that all pieces of organic material greater than ½ inch in diameter be picked out of the fill before it is compacted. Any organic-rich soil derived from earthwork activities should be utilized in landscape areas or wasted off site. Imported Structural Fill: The appropriate type of imported structural fill will depend on weather conditions. During extended periods of dry weather, we recommend imported fill, at a minimum, meet the requirements of Common Borrow as specified in Section 9-03.14(3) of the most current version of the Washington State Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard Specifications). During wet weather, higher-quality structural fill might be required, as Common Borrow may contain sufficient fines to be moisture sensitive. During wet weather we recommend that imported structural fill meet the requirements of Gravel Borrow as specified in Section 9-03.14(1) of the WSDOT Standard Specifications. Prior to importing structural fill, we recommend we be provided a sample of the material to evaluate its suitability for use as structural fill. Retaining Wall Backfill: Cast-in-place concrete foundation retaining walls should include a drainage fill zone extending at least 2 feet back from the back face of wall for the entire wall height. The drainage fill should meet the requirements of Gravel Backfill for Walls as specified in Section 9-03.12(2) of the WSDOT Standard Specifications. Compaction Criteria: Our recommendations for soil compaction are summarized in the following table. Structural fill for roadways and utility trenches in municipal rights-of-way should be placed and compacted in accordance with the jurisdiction codes and standards. We recommend that a geotechnical engineer be present during grading so that an adequate number of density tests may be conducted as structural fill placement occurs. In this way, the adequacy of the earthwork may be evaluated as it proceeds. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 8 Moisture Content: Structural fill should be placed at a moisture content within plus or minus two percent of optimum moisture content as determined by the ASTM D-1557 test method (modified proctor). Imported structural fill should be delivered to the site at the recommended moisture content for compaction. Structural fill with a moisture content greater than two percent above optimum should be moisture conditioned by windrowing and drying or wasted off site. Structural fill with a moisture content less than two percent below optimum should be blended with water to achieve the recommended moisture content. Fill Placement: Structural fill should be placed in horizontal lifts with a loose lift thickness appropriate for the material and energy of the compaction equipment used. If loose lift thickness greater than 12 inches are desired, the contractor should be required to demonstrate that the combination of fill material and compaction equipment can compact the entire lift thickness to the specified levels. Each lift of fill should be compacted to the minimum levels recommended above based on the maximum laboratory dry density as determined by the ASTM D1557 Modified Proctor Compaction Test. Underground Utilities We recommend that utility trenching conform to all applicable federal, state, and local regulations, such as OSHA and WISHA, for open excavations. Trench excavation safety guidelines are presented in WAC Chapter 296-155 and WISHA RCW Chapter 49.17. Utility Subgrade Preparation: We recommend that all utility subgrades be firm and unyielding and free of all soils that are loose, disturbed, or pumping. Such soils should be removed and replaced, if necessary. All structural fill used to replace over-excavated soils should be compacted as recommended in the Structural Fill section of this report. If utility foundation soils are soft, we recommend that they be over- excavated 12 inches and replaced with crushed rock. RECOMMENDED SOIL COMPACTION LEVELS Location Minimum Percent Compaction* All fill below building floor slabs and foundations 95 Upper 2 feet of fill below pavements 95 Pavement fill below 2 feet 92 Retaining wall backfill less 3 feet from back of wall face 92** Upper 2 feet of utility trench backfill 95 Utility trenches below 2 feet 92 Landscape Areas 90 ASTM D1557 Modified Proctor Maximum Dry Density Care must be taken not to over-compact retaining wall backfill as over-compaction can induce stresses in excess of design stresses. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 9 Structures such as manholes and catch basins which extend into soft soils should be underlain by at least 12 inches of crushed gravel fill compacted to at least 90 percent of the modified Proct or maximum dry density. This granular material could consist of crushed rock, quarry spalls, or coarse crushed concrete. Alternatively, quarry spalls or pea gravel could be used until above the water level in wet utility excavations. It may be necessary to place a geotextile fabric over the native subgrade soils if they are too soft, to provide a separation between the bedding and subgrade soils. Bedding: We recommend that a minimum of 4 inches of bedding material be placed above and below all utilities or in general accordance with the utility manufacturer’s recommendations and local ordinances. We recommend that pipe bedding consist of Gravel Backfill for Pipe Zone Bedding as specified in Section 9-03.12(3) of the WSDOT Standard Specifications. All trenches should be wide eno ugh to allow for compaction around the haunches of the pipe, or material such as pea gravel should be used below the spring line of the pipes to eliminate the need for mechanical compaction in this portion of the trenches. If water is encountered in the excavations, it should be removed prior to fill placement. Trench Backfill: Materials, placement, and compaction of utility trench backfill should be in accordance with the recommendations presented in the Structural Fill section of this report. Based on our review of preliminary civil engineering drawings, deep excavations approaching 20 feet will be required for installation of some utilities. It is imperative that care be taken during backfilling of deep utility excavations. Initial lift thicknesses over pipes should not exceed 1 foot. If there is concern about utility damage, the initial lift thickness should be compacted with light, hand operated compaction equipment. All subsequent trench backfill lifts should not exceed 1 foot in loose thickness. Temporary and Permanent Slopes Temporary excavation slope stability is a function of many factors, including: The presence and abundance of groundwater; The type and density of the various soil strata; The depth of cut; Surcharge loadings adjacent to the excavation; and The length of time the excavation remains open. As the cut is deepened, or as the length of time an excavation is open, the likelihood of bank failure increases; therefore, maintenance of safe slopes and worker safety should remain the responsibility of the contractor, who is present at the site, able to observe changes in the soil conditions, and monitor the performance of the excavation. It is exceedingly difficult under the variable circumstances to pre-establish a safe and “maintenance-free” temporary cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe temporary slope configurations since the contractor is continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and groundwater DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 10 conditions encountered. Unsupported vertical slopes or cuts deeper than 4 feet are not recommended if worker access is necessary. The cuts should be adequately sloped, shored, or supported to prevent injury to personnel from local sloughing and spalling. The excavation should conform to applicable Federal, State, and Local regulations. According to Chapter 296-155, Part N of the Washington Administrative Code (WAC), the contractor should make a determination of excavation side slopes based on classification of soils encountered at the time of excavation. For planning purposes, we recommend temporary excavations within the upper 15 feet of existing site grades be planned no steeper than 1H:1V (horizontal to vertical). Temporary excavations completed in the very dense glacial till soils observed in our explorations (typically observed below 15 feet from existing site grades) should be planned not steeper than 0.75H:1V. Temporary cuts may need to be constructed at flatter angles based upon the soil moisture and groundwater conditions at the time of construction. Adjustments to the slope angles should be determined by the contractor at that time. Temporary excavations that extend below the groundwater table will not be adequately stable unless dewatered. Groundwater levels should be maintained a minimum of two feet below the bottom of temporary excavations. We recommend that all permanent cut or fill slopes constructed in native soils or with imported structural fill be designed at a 2H:1V (Horizontal:Vertical) inclination or flatter. However, consideration should be given regarding creation of slopes that would meet the criteria for Protected Slopes as defined by the Code (slopes greater than 40% with vertical rise of 15 feet or more) as buffers and setbacks would be required from these slopes. If the slopes are exposed to prolonged rainfall before vegetation becomes established, the surficial soils will be prone to erosion and possible shallow sloughing. We recommend covering permanent slopes with a rolled erosion protection material, such as composite straw or coir matting or Curlex II, if vegetation has not been established by the regional wet season (typically November through May). Residential Building Foundations Based on our analyses, conventional, shallow spread footings appear feasible for support of residential structure foundation loads provided that the foundation subgrades are prepared in accordance with this report. Recommendations for shallow spread footings are provided below. General Footing Subgrade Preparation Soils encountered at footing subgrade elevation are expected to consist of either fill placed to raise site grades, or native soils exposed in cut areas. Prior to placement of form work and reinforcement, footing subgrades in fill areas should be compacted to a firm and unyielding condition. In cut areas, where footings will be founded on native soils, we recommend footing subgrades be evaluated by a representative from ZGA to evaluate the need for compaction. In some areas, where footing subgrades are less than about 15 feet below existing site grade, footing subgrades may require compaction. The DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 11 need for compaction of native soil footing subgrades should be evaluated on a case-by-case basis by a representative from ZGA. Soils exposed at footing subgrade elevation (in fill or cut areas) will be highly susceptible to disturbance during wet weather. For this reason, if wet weather is expected, we recommend considering protection of footing subgrades through placement of a thin layer of controlled density fill (CDF). Shallow Foundation Allowable Bearing Pressure For footings founded less than 15 feet below existing site grade or on structural fill placed to raise site grades, we recommend using an allowable bearing pressure of 2,000 psf. For footings founded greater than 15 feet below existing site grade (possibly in the vicinity of Lots 1, 2, and 3), an allowable bearing pressure of 4,000 psf may be used. A one-third increase of the bearing pressure recommended above may be used for short-term transient loads such as wind and seismic forces. Shallow Foundation Depth and Width For frost protection, the bottom of all exterior footings should bear at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings should bear at least 12 inches below the surrounding slab surface level (unless otherwise noted below). We recommend that all continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively. The project currently includes several site retaining walls that will be located in very close proximity to, and in some cases, connected to the proposed residential structures. The design of shallow foundation depths must consider the potential for surcharge loading on site retaining walls. We recommend that shallow foundation depths be designed to NOT surcharge site retaining walls if feasible. To prevent house foundations from surcharging site retaining walls, the foundation subgrade elevation of house foundations should be located below a 1H:1V line projected up from the back toe of site retaining walls. In locations where house foundations cannot be founded at a depth to eliminate surcharges on site retaining walls, we recommend site retaining walls be designed for the surcharge loading and consist of stiff walls such as reinforced concrete. We should be consulted to provide surcharge loading in this case. Lateral Resistance Resistance to lateral loads can be calculated assuming an ultimate soil passive resistance of 400 pcf equivalent fluid pressure (triangular distribution) and an ultimate base friction coefficient of 0.50. An appropriate safety factor (or load/resistance factors) should be included for calculating resist ance to lateral loads. For allowable stress design, we recommend a minimum 1.5 safety factor. We recommend that passive resistance be neglected in the upper 18 inches of embedment. The above-recommended soil passive resistance assumes any structural fill used to backfill footing excavations is compacted in accordance with the recommendations presented in this report. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 12 Estimated Foundation Settlements Total settlement of footings for service load conditions founded on a subgrade prepared as recommended in this report are estimated to be less than 1 inch. Differential settlement is estimated to be about ½ inch or less in 40 feet. Permanent Foundation Retaining Walls As currently proposed, the residential structures for this project will include backfilled, permanent foundation retaining walls with a maximum anticipated exposed height of about 16 feet. The lateral soil pressures acting on backfilled retaining walls will depend on the nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth loads. Yielding walls (i.e. walls that are free to translate or rotate) that are able to displace laterally at least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non-yielding walls (i.e. walls that are not free to translate or rotate) should be designed for at-rest earth pressures. We recommend yielding walls be designed for the following active lateral earth pressures: Backslope Condition Equivalent Fluid Density Level 38 pcf 3H:1V 50 pcf 2H:1V 56 pcf If non-yielding walls are expected, we should be consulted to provide recommended lateral earth pressures. For resistance to lateral loads, the values provided above in the Building Foundations section may be utilized. The above-recommended lateral earth pressures assume that adequate drainage measures are provided to limit the potential for buildup of hydrostatic pressures. All backfilled walls should include a drainage aggregate zone extending a minimum of two feet from the back of wall for the full height of the wall and wide enough at the base of the wall to allow seepage to flow to the footing drain. The drainage aggregate should consist of material meeting the requirements of WSDOT 9-03.12(2), Gravel Backfill for Walls. A minimum 4-inch diameter, perforated PVC drain pipe should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate discharge point. We recommend placing a non- woven geotextile, such as Mirafi 140N, or equivalent, around the free draining backfill material. It should be noted that site soils will not meet the criteria for Gravel Backfill for Walls. As an alternative to the drainage aggregate zone, the use of a dimple core drainage composite (DCDC) such as Mirafi G100N or equivalent could be considered. The use of a DCDC still requires a footing drain at the base of retaining walls enveloped in gravel and a woven geotextile. The use and installation of DCDCs should be in strict accordance with the manufacturers recommendations. In addition to retaining wall drainage measures, we recommend the project team consider water proofing foundation walls with Volclay panels or similar measures. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 13 Site Retaining Walls As currently proposed, the project will include several site retaining walls to support cuts and fills. For fill walls, we recommend the use of geogrid-reinforced, segmental block walls commonly referred to as mechanically stabilized earth or MSE walls. For cut walls, rockeries or gravity block walls could be considered. Recommendations for specific retaining wall types are provided below. As mentioned in the Shallow Foundation Width and Depth section above, the design of site retaining walls must consider the potential for surcharge loading from house foundation loads if applicable. Rockeries Rockery Subgrade We recommend founding the rockeries on a native soil subgrade consisting of at least medium dense granular soils, or structural fill compacted to at least 95 percent of the modified Proctor maximum dry density as determined by the ASTM D 1557 test method. We recommend that a representative from our firm evaluate rockery subgrade conditions prior to placement of the first layer of rocks. Rockery Wall Design and Construction We recommend the design and construction of rockeries be completed in accordance with Pierce County Standard Detail PC.D1.1. It should be noted that Pierce County limits the total height (exposed plus embedded depth) of cut rockeries to 5 feet. Based on our review of the City of Renton Municipal Code, we could find no reference to the maximum allowable height of cut rockeries. It is our opinion that rockeries up to 6 feet total height may be constructed at the site using Pierce County Standard Detail PC.D1.1. We recommend an engineered design be completed for proposed rockeries in excess of 6 feet in total height. MSE and Gravity Block Walls MSE and Gravity Block Wall Subgrade We recommend founding MSE walls and gravity block walls on a native soil subgrade consisting of at least medium dense granular soils, or structural fill compacted to at least 95 percent of the modified Proctor maximum dry density as determined by the ASTM D 1557 test method. Prior to placement of crushed rock leveling pads for MSE or gravity block walls, we recommend a representative from ZGA evaluate the subgrade. MSE and Gravity Block Wall Design and Construction We recommend the design and construction of MSE and gravity block walls be completed in strict accordance with the recommendations presented in the National Concrete Masonry Association’s 2016 Segmental Retaining Walls Best Practices Guide. Design of MSE walls should be completed using the following soil design parameters: DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 14 Soil Properties Reinforced Backfill Retained Soil Foundation Soil Unit Weight (pcf) 130 125 1251/1352 Friction Angle (degrees) 34 32 321/362 Cohesion (psf) 0 0 0 Peak Ground Acceleration (As) 0.469g 1For fill walls in the western portion of the site or cut walls in the eastern portion of the site where wall subgrade elevation is less than 15 feet below existing site grade. 2For cut walls in the eastern portion of the site where wall subgrade elevation is greater than 15 feet below existing site grade. We recommend reinforced backfill for MSE walls meet the requirements for Common Borrow, Option 2 as specified in Section 9-03.14(3) of the WSDOT Standard Specifications. Backfill placement and compaction, and subgrade preparation should be completed in accordance with the recommendations presented in this report. Stormwater Infiltration Feasibility Local stormwater codes require an evaluation of stormwater infiltration feasibility. The project site is bordered to the west by a Protected Slope / High Landslide Hazard Area. It is our opinion that infiltrating stormwater at this site could have an adverse impact on stability of the steep slope that borders the site to the west. As such, it is our opinion that stormwater infiltration should be considered infeasible for this project. Stormwater Detention Vault Current plans indicate an approximate 2,400 square feet underground detention vault will be constructed in the NE 38th Street right-of-way, north of the project site. The plans indicate the bottom of the vault will be at about elevation 121 feet. Existing grade in the vicinity of the vault ranges from about 136 to 142 feet. Therefore, cuts on the order of 15 to 21 feet below existing site grades will be required for construction of the vault. The vault may be designed using lateral earth pressure and lateral resistance values provided above. The vault may be designed assuming an allowable bearing pressure of 4,000 psf. The vault walls should be drained in accordance with the recommendations provided in the Permanent Foundation Retaining Wall section above. Current plans for the stormwater vault show the vault discharges into a ditch that runs parallel to the NE 38th Street right-of-way, west of the site. The NE 38th Street right-of-way bisects a steep slope in this area, and the discharge would introduce concentrated runoff parallel to the top of this slope. This could result in adverse impacts to the stability of this slope. We recommend the project team consider alternatives such as discharging to Lincoln Avenue NE, tight lining down the NE 38th right-of-way, or a lined ditch. On-Grade Concrete Slabs The following sections provide recommendations for on-grade floor slabs. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 15 Subgrade Preparation Subgrades for on-grade slabs should be prepared in accordance with the Site Preparation and Structural Fill sections of this report. Capillary Break To provide a capillary break, uniform slab bearing surface, and a minimum subgrade modulus of 150 pci, we recommend the on-grade slabs be underlain by a 6-inch thick layer of compacted, granular fill contain less than 5 percent fines, based on that soil fraction passing the U.S. No. 4 sieve. The use of a capillary break need only be considered for the residential structures. Vapor Retarder The use of a vapor retarder should be considered beneath concrete slabs on grade that will be covered with wood, tile, carpet or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture or is otherwise considered moisture-sensitive. When conditions warrant the use of a vapor retarder, the slab designer and contractor should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder. Permanent Drainage Considerations Surface Drainage As currently proposed, finished grades in many areas of the site are designed to direct surface water flow towards homes. Typically, we recommend final site grades should be sloped to carry surface water away from buildings and other drainage-sensitive areas. If site grades must be designed to direct flow towards homes, we recommend surface water runoff collection systems such as catch basins, slot drains, french drains, etc. be designed to collect and discharge surface water draining towards homes to the site stormwater drainage system. Additionally, site grades should be designed such that concentrated runoff on softscape surfaces is avoided. Any surface runoff directed towards softscaped slopes should be collected at the top of the slope and routed to the bottom of the slo pe and discharged in a manner that prevents erosion. Perimeter Foundation Drains We recommend all the homes be designed with a perimeter foundation drain. The drain should consist of a 4 inch diameter perforated drain pipe surrounded by a minimum of 12 inches of free draining gravel. We recommend placing a non-woven geotextile, such as Mirafi 140N, or equivalent, around the free draining backfill material. The perforated pipe should be tight lined to the stormwater drainage system. Roof drain systems should be independent of footing drains. Adequate drainage measures above footing drains for backfilled retaining walls as recommend above, should be installed. CLOSURE The analysis and recommendations presented in this report are based, in part, on the explorations completed for this study. The number, location, and depth of the explorations were completed within the DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Proposed 38th Street Short Plat Project No. 2002.01 October 12, 2018 Page 16 constraints of budget and site access so as to yield the information to formulate our recommendations. Project plans were in the preliminary stage at the time this report was prepared. We therefore recommend Zipper Geo Associates, LLC be provided an opportunity to review the final plans and specifications when they become available in order to assess that the recommendations and design considerations presented in this report have been properly interpreted and implemented into the project design. The performance of earthwork, structural fill, foundations, and pavements depend greatly on proper site preparation and construction procedures. We recommend that Zipper Geo Associates, LLC be retained to provide geotechnical engineering services during the earthwork-related construction phases of the project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer could provide additional geotechnical recommendations to the contractor and design team in a timely manner as the project construction progresses. This report has been prepared for the exclusive use of KP Development and their agents, for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Zipper Geo Associates, LLC reviews the changes and either verifies or modifies the conclusions of this report in writing. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 FIGURE Job No. Zipper Geo Associates, LLC 19019 36th Ave. W.,Suite E Lynnwood, WA SHT. of11 SITE AND EXPLORATION PLAN 2002.01OCT. 2018 1 38TH STREET SHORT PLAT 1825 NE 38TH STREET RENTON, WASHINGTON SCALE IN FEET 040 4020 LEGEND B-1 BORING NUMBER AND APPROXIMATE LOCATION BASE MAP REFERENCE:PRELIMINARY CIVIL PLANS PROVIDED BY PREFERRED ENGINEERING, LLC DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 APPENDIX A SUBSURFACE EXPLORATION PROCEDURES & LOGS DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS Field Exploration Description Our field exploration for this project included 2 test borings completed on 4/27/18. The approximate exploration locations are shown on the Site and Exploration Plan, Figure 1. Exploration locations were determined by measuring off of existing site features shown on a site plan completed by the project civil engineer. The approximate ground surface elevation at the exploration locations was determined by interpolating from topographic information shown on the above-referenced site plan. As such, the exploration locations and elevations should be considered accurate only to the degree implied by the means and methods used to define them. Boring Procedures Our exploratory borings were advanced with a hollow stem auger, using a track-mounted drill rig operated by an independent drilling firm working under subcontract to our fir m. An engineer from our firm continuously observed the borings, logged the subsurface conditions encountered, and obtained representative soil samples. Al l samples were stored in moisture-tight containers and transported to our laboratory for further visual classification and testing. After each boring was completed, the borehole was backfilled with bentonite clay. Throughout the drilling operation, soil samples were obtained at 2.5- to 5-foot depth intervals by means of the Standard Penetration Test (ASTM: D-1586). This testing and sampling procedure consists of driving a standard 2 - inch outside diameter steel split spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches. The number of blows required to drive the sampler through each 6 -inch interval is recorded, and the total number of blows struck during the final 12 inches is recorded as the Standard Penetration Resistance , or “blow count” (N value). If a total of 50 blows is struck within any 6-inch interval, the driving is stopped and the blow count is recorded as 50 blows for the actual penetration distance. The resulting Standard Penetration Resistance values indicate the relative density of granular soils and the relative consistency of cohesive soils. The enclosed boring logs describe the vertical sequence of soils and materials encountered in each boring, based primarily upon our field classifications and supported by our subsequent laboratory examination and testing. Where a soil contact was observed to be gradational, our logs indicate the average contact depth. Where a soil type changed between sample intervals, we inferred the contact depth. Our logs also graphically indicate the blow count, sample type, sample number, and approximate depth of each soil sample obtained from the boring, as well as any laboratory tests performed on these soil samples. If any groundwater was encountered in a borehole, the approximate groundwater depth, and date of observation, is depicted on the log. Groundwater depth estimates are typically based on the moisture content of soil samples, the wetted portion of the drilling rods, the water level measured in the borehole after the auger has been extracted, or through the use of an observation well. The boring logs presented in this appendix are based upon the drilling action, observation of the samples secured, laboratory test results, and field logs. The various types of soils are indicated as well as the depth where the soils or characteristics of the soils changed. It should be noted that these changes may have been gradual, and if the changes occurred between samples intervals, they were inferred. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm) 2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube sample Bentonite Liquid Limit Grout/Concrete Screened Casing TESTING KEY Blank Casing GSA = Grain Size Analysis 200W = 200 Wash Analysis Date:Project No.: Consol. = Consolidation Test Att. = Atterberg Limits Boring Location: Sample Number SAMPLES Recovery ( in.)Depth (ft)SOIL DESCRIPTION Date Drilled: The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information.Ground WaterPENETRATIONRESISTANCE (blows/foot)B-1 B-1 2002.01Blow Counts38th Street Short Plat 1825 NE 38th Street Zipper Geo Associates 19019 36th Ave. W, Suite E Lynnwood, WA Renton, Washington Page 1 of 2 BORING LOG:TestingPlastic Limit Groundwater level at time of drilling (ATD) or on date of measurement. Natural Water Content 0 20 40 60 10 18 10 18 18 18 S-1 S-2 S- 3 S- 4 S- 5 S-6 0 5 10 15 20 25 See Figure 1, Site and Exploration Plan 183 ft 4/ 27/ 2018 Advance Drill Hollow Stem Auger D50 8 Auto 11/ 2/ 121 10 50/ 5 23 78 35 MC MC MC MC MC SNM 6 inches of forest duff over brown SILT with organics Very loose, wet, tan-brown, SILT, with sand and organics, trace gravel Loose, wet, tan-brown, SILT, some sand, with a lens of sand. Slight mottling Very dense, wet, tan, SAND, with to some silt, trace gravel blow counts overstated) Medium dense, moist, tan-gray, SAND, some silt, trace gravel Very dense, moist, tan- gray, silty SAND to sandy SILT, DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm) 2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube sample Bentonite Liquid Limit Grout/Concrete Screened Casing TESTING KEY Blank Casing GSA = Grain Size Analysis 200W = 200 Wash Analysis Date:Project No.: Consol. = Consolidation Test Att. = Atterberg Limits Boring Location: B-1 Date Drilled: Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (in.)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsTesting1825 NE 38th Street The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Plastic Limit Natural Water Content 38th Street Short Plat Groundwater level at time of drilling (ATD) or on date of measurement.Renton, Washington 2002.01 Zipper Geo Associates 19019 36th Ave. W, Suite E Lynnwood, WABORING LOG: B- 1 Page 2 of 2 18S-7 18 18 18 S- 8 S- 9 S- 10 0 20 40 60 25 30 35 40 45 50 See Figure 1, Site and Exploration Plan 183 ft 4/ 27/ 2018 Advance Drill Hollow Stem Auger D50 8 Auto 11/2/1250/4 17 27 28 SNM Hard, moist, gray, SILT, some sand, moderate mottling Very dense, moist, gray, SAND, with gravel, some silt Very stiff, moist, gray, clayey SILT, some to trace sand, trace gravel Very stiff, moist, gray, clayey SILT, some sand Very stiff, moist, gray, SILT, some to trace sand Boring completed at approximately 41 1/ DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm) 2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube sample Bentonite Liquid Limit Grout/Concrete Screened Casing TESTING KEY Blank Casing GSA = Grain Size Analysis 200W = 200 Wash Analysis Date:Project No.: Consol. = Consolidation Test Att. = Atterberg Limits Boring Location: Sample Number SAMPLES Recovery ( in.)Depth (ft)SOIL DESCRIPTION Date Drilled: The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information.Ground WaterPENETRATIONRESISTANCE (blows/foot)B-2 B-2 2002.01Blow Counts38th Street Short Plat 1825 NE 38th Street Zipper Geo Associates 19019 36th Ave. W, Suite E Lynnwood, WA Renton, Washington Page 1 of 2 BORING LOG:TestingPlastic Limit Groundwater level at time of drilling (ATD) or on date of measurement. Natural Water Content 0 20 40 60 6 12 14 12 12 18 S-1 S-2 S- 3 S- 4 S- 5 S-6 0 5 10 15 20 25 See Figure 1, Site and Exploration Plan 144 ft 4/ 27/ 2018 Advance Drill Hollow Stem Auger D50 8 Auto 11/ 2/ 127 9 16 19 32 21 MC MC MC MC MC SNM 8 inches of grass and moss over, brown SAND with silt Loose, moist, tan, SAND, some silt (fill)Loose, moist, tan, SAND, some silt, trace gravel Medium dense, wet, tan, SAND, with silt, trace gravel Medium dense, wet, tan, SILT, with sand, some gravel, moderate mottling Dense, wet, tan, SAND, some silt and gravel DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 Drilling Company:Bore Hole Dia.: Top Elevation:Drilling Method:Hammer Type: Drill Rig:Logged by: Standard Penetration Test Hammer Weight and Drop: SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm) 2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content 3-inch I.D. Shelby tube sample Bentonite Liquid Limit Grout/Concrete Screened Casing TESTING KEY Blank Casing GSA = Grain Size Analysis 200W = 200 Wash Analysis Date:Project No.: Consol. = Consolidation Test Att. = Atterberg Limits Boring Location: B-2 Date Drilled: Depth (ft)SOIL DESCRIPTION Sample Number SAMPLES Recovery (in.)Ground WaterPENETRATION RESISTANCE (blows/foot)Blow CountsTesting1825 NE 38th Street The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Plastic Limit Natural Water Content 38th Street Short Plat Groundwater level at time of drilling (ATD) or on date of measurement.Renton, Washington 2002.01 Zipper Geo Associates 19019 36th Ave. W, Suite E Lynnwood, WABORING LOG: B- 2 Page 2 of 2 12S-7 16 12 2 S- 8 S- 9 S- 10 0 20 40 60 25 30 35 40 45 50 See Figure 1, Site and Exploration Plan 144 ft 4/ 27/ 2018 Advance Drill Hollow Stem Auger D50 8 Auto 11/2/1250/2 53 50/6 50/4 SNM Very dense, moist, tan, gravelly SAND, some silt Very dense, wet, gray-tan, SAND, with silt, some gravel Very dense, moist, SAND, with silt, some to trace gravel, moderate mottling Very dense, moist, silty SAND, some gravel Boring was completed at approximately 41 1/ 2 feet. No groundwater was observed during time of drilling. Driller reported seepage from side walls DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 APPENDIX B LABORATORY TESTING PROCEDURES & RESULTS DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS A series of laboratory tests were performed by ZGA and a subcontract testing laboratory during the course of this study to evaluate the index and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests performed are given below. Visual Classification Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in moisture tight containers and transported to our laboratory where the field classifications were verified or modified as required. Visual classification was generally done in accordance with ASTM D2488. Visual soil classification includes evaluation of color, relative moisture content, soil type based upon grain size, and accessory soil types included in the sample. Soil classifications are presented on the exploration logs in Appendix A. Moisture Content Determinations Moisture content determinations were performed on representative samples obtained from the explorations in order to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM D 2216. Moisture contents are presented on the exploration logs in Appendix A. DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11 DocuSign Envelope ID: 13FB31B7-5A77-4DF8-9AA5-1ABE6F99CC11