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HomeMy WebLinkAboutRS_Geotechnical_Report_221014_V1    GEOTECHNICAL REPORT Vision House Children’s Village Northeast 4th Street and Bremerton Avenue Northeast Renton, Washington Project No. T-8706 Prepared for: Pavillon, LLC Redmond, Washington April 15, 2022     April 15, 2022 Project No. T-8706 Mr. Steven Jewett Pavillon, LLC 8201—164th Avenue Northeast, Suite 260 Redmond, Washington 98052 Subject: Geotechnical Report Vision House Children’s Village Northeast 4th Street and Bremerton Avenue Northeast Renton, Washington Dear Mr. Jewett: As requested, we have conducted a geotechnical engineering study for the subject project. The attached report presents our findings and recommendations for the geotechnical aspects of project design and construction. The soil conditions observed in the test pits can be divided into two sections. In the northern half of the site, soil conditions generally consisted of four to five inches of sod overlying six to seven feet of fill material composed of loose to medium dense silty sand with gravel and various amounts of roots, glass, plastic, wood, and concrete debris inclusions over three to four feet of dense to very dense silty sand with varying gravel (weathered and unweathered glacial till) to the termination of the test pits. In the southern half of the site, soil conditions consisted of approximately twelve inches of topsoil overlying approximately two feet of possible fill composed of medium dense silty sand over dense to very dense silty sand with gravel (unweathered glacial till) to the termination of the test pits. No groundwater was observed in our explorations. In our opinion, the soil conditions we observed at the site will be suitable for support of the proposed development, provided the recommendations presented in this report are incorporated into project design and construction. 12220 113th Avenue NE, Ste. 130, Kirkland, Washington 98034  Phone (425) 821‐7777 • Fax (425) 821‐4334  4-15-2022     TABLE OF CONTENTS Page No. 1.0 Project Description ........................................................................................................... 1 2.0 Scope of Work ................................................................................................................. 1 3.0 Site Conditions ................................................................................................................. 2 3.1 Surface ................................................................................................................ 2 3.2 Subsurface ........................................................................................................... 2 3.3 Groundwater ....................................................................................................... 3 3.4 Geologically Hazardous Areas ............................................................................ 3 3.4.1 Erosion Hazard Areas ................................................................................ 3 3.4.2 Flood Hazard Areas ................................................................................... 4 3.4.3 Steep Slope and Landslide Hazard Areas ................................................. 4 3.4.4 Seismic Hazard Areas ............................................................................... 5 3.4.5 Coal Mine Hazard Areas ........................................................................... 5 3.5 Seismic Design Parameters ................................................................................. 5 4.0 Discussion and Recommendations ................................................................................... 6 4.1 General ................................................................................................................ 6 4.2 Site Preparation and Grading .............................................................................. 6 4.3 Excavation, Shoring, and Dewatering ................................................................. 7 4.4 Foundation Support ............................................................................................. 9 4.5 Floor Slab-on-Grade ......................................................................................... 10 4.6 Lateral Earth Pressures ...................................................................................... 10 4.7 Stormwater Facilities ........................................................................................ 11 4.8 Infiltration Feasibility ....................................................................................... 12 4.9 Drainage ............................................................................................................ 12 4.10 Utilities .............................................................................................................. 11 4.11 Pavement ........................................................................................................... 12 5.0 Additional Services ........................................................................................................ 13 6.0 Limitations ..................................................................................................................... 13 Figures Vicinity Map ......................................................................................................................... Figure 1 Exploration Location Plan..................................................................................................... Figure 2 Earth Pressure Loading Diagram on Cantilevered Soldier Pile Shoring ............................... Figure 3 Lateral Earth Pressure on Basement Walls ........................................................................... Figure 4 Soldier Pile Wall Drainage Detail ......................................................................................... Figure 5 Typical Wall Drainage Detail ............................................................................................... Figure 6 Appendix Field Exploration and Laboratory Testing ....................................................................... Appendix A Geotechnical Report Vision House Children’s Village Northeast 4th Street and Bremerton Avenue Northeast Renton, Washington 1.0 PROJECT DESCRIPTION The project consists of redeveloping the site with a four-story multi-use building, with one level of below grade parking, an educational/communal area and two levels of residential housing, along with associated access and utilities. Grading and design details were not available at the time of this report. With one level of below grade parking, excavation depths of 10 to 12 feet are expected to achieve foundation levels. As we understand, the structure will be a three-story building with one level of below grade parking. Structural loading is expected to be moderate with isolated building columns carrying 280 to 400 kips and continuous bearing walls carrying 4 to 8 kips per foot. The recommendations in the following sections of this report are based on the design discussed above. If actual features vary or changes are made, we should review the plans in order to modify our recommendations, as required. We should review final design drawings and specifications to verify that our recommendations have been properly interpreted and incorporated into the project design. 2.0 SCOPE OF WORK Our work was completed in accordance with our authorized proposal, dated January 7, 2022. Accordingly, on February 7, 2022, we observed soil and groundwater conditions at 4 test pits to depths ranging from 8 to 11 feet below existing surface grades using a track-mounted mini excavator. Using this data along with laboratory testing, we performed analyses to develop geotechnical recommendations for project design and construction. Specifically, this report addresses the following:  Soil and groundwater conditions.  Geologic hazards per the City of Renton Municipal Code.  Seismic criteria per the current International Building Code (IBC).  Site preparation and grading.  Excavation, shoring, and dewatering.  Foundations.  Floor slabs. April 15, 2022 Project No. T-8706 Page No. 2    Lateral earth pressure for wall design.  Stormwater facilities.  Infiltration feasibility.  Drainage.  Utilities.  Pavements. It should be noted that recommendations outlined in this report regarding drainage are associated with soil strength, design earth pressures, erosion, and stability. Design and performance issues with respect to moisture as it relates to the structural environment are beyond Terra Associates’ purview. A building envelope specialist or contractor should be consulted to address these issues, as needed. 3.0 SITE CONDITIONS 3.1 Surface The project site consists of a single tax parcel totaling approximately 1.2 acres located immediately east of the existing building at 450 Bremerton Avenue Northeast in Renton, Washington. The approximate site location is shown on Figure 1. The northern portion of the site is partially developed with a children’s playground, basketball court and associated parking and the southern portion of the site is undeveloped and covered with light to moderate vegetation and trees. Site topography consists of a slight to moderate slope that descends from the west-northwest to the east- southeast with an overall relief of approximately 20 feet. Review of the Google Earth™ historical imagery, a structure previously existed on the site between Test Pits TP-2 and TP-3 which was demolished sometime between 2002 and 2005. 3.2 Subsurface The soil conditions observed in the test pits can be divided into two sections. In the northern half of the site, soil conditions generally consisted of four to five inches of sod overlying six to seven feet of fill material composed of loose to medium dense silty sand with gravel and various amounts of roots, glass, plastic, wood and concrete debris inclusions over three to four feet of dense to very dense silty sand with varying gravel (weathered and unweathered glacial till) to the termination of the test pits. In the southern half of the site, soil conditions consisted of approximately twelve inches of topsoil overlying approximately two feet of possible fill composed of medium dense silty sand over dense to very dense silty sand with gravel (unweathered glacial till) to the termination of the test pits. April 15, 2022 Project No. T-8706 Page No. 3   The Geologic Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965), shows site soils mapped as Ground moraine deposits (Qgt). The native soils observed in the test pits are generally consistent with this geologic mapping. The preceding discussion is intended to be a general review of the soil conditions encountered. For more detailed descriptions, please refer to the Test Pit Logs in Appendix A. The approximate locations of the test pits are shown on Figure 2. 3.3 Groundwater No groundwater was observed during the exploration, additionally, no mottling was observed. The test pits were not opened for an extended period of time. Therefore, based on our experience with the soil types observed, it is possible that seasonal perched groundwater seepage develops during the wet winter months. 3.4 Geologic Hazards Section 4-3-050G of the Renton Municipal Code (RMC) defines geologically hazardous areas as “areas which may be prone to one or more of the following conditions: erosion, flooding, landslides, coal mine hazards, or seismic activity.” 3.4.1 Erosion Hazard Areas Section 4-3-050G 5.c of the RMC defines erosion hazard areas as: “i. Low Erosion Hazard (EL): Areas with soils characterized by the Natural Resource Conservation Service (formerly U.S. Soil Conservation Service) as having slight or moderate erosion potential, and a slope less than fifteen percent (15 percent). ii. High Erosion Hazard (EH): Areas with soils characterized by the Natural Resource Conservation Service (formerly U.S. Soil Conservation Service) as having severe or very severe erosion potential, and a slope more than fifteen percent (15 percent).” The soils observed within the site are classified as Alderwood Gravelly Sandy Loam, 8 to 15 percent slopes (AgC). by the United States Department of Agriculture Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service. With the existing site gradients, the soils will have a moderate potential for erosion when exposed. Therefore, the site is a low erosion hazard area per the RMC. Erosion protection measures as required by the City of Renton will need to be in place prior to starting grading activities on the site. This would include perimeter silt fencing to contain erosion onsite and cover measures to prevent or reduce soil erosion during and following construction. April 15, 2022 Project No. T-8706 Page No. 4   3.4.2 Flood Hazard Areas Section 4-3-050G 4.a of the RMC defines flood hazard areas as “the land in the floodplain subject to one percent or greater chance of flooding in any given year. Designation on flood maps always includes the letters A or V.” Based on a review of the project site and topography, the area is not within a mapped flood hazard area. Therefore, the site would not be considered a flood hazard area. 3.4.3 Steep Slope and Landslide Hazard Areas Section 4-3-050G 5.a of the RMC defines steep slope hazard areas as: “i. Sensitive Slopes: A hillside, or portion thereof, characterized by: (a) an average slope of 25 percent to less than 40 percent as identified in the City of Renton Steep Slope Atlas or in a method approved by the City; or (b) an average slope of 40 percent or greater with a vertical rise of less than 15 feet as identified in the City of Renton Steep Slope Atlas or in a method approved by the City; (c) abutting an average slope of 25 percent to 40 percent as identified in the City of Renton Steep Slope Atlas or in a method approved by the City. This definition excludes engineered retaining walls. ii. Protected Slopes: A hillside, or portion thereof, characterized by an average slope of 40 percent or greater grade and having a minimum vertical rise of 15 feet as identified in the City of Renton Steep Slope Atlas or in a method approved by the City.” Section 4-3-050G 5.b defines landslide hazard areas as: “i. Low Landslide Hazard (LL): Areas with slopes less than 15 percent. ii. Medium Landslide Hazard (LM): Areas with slopes between 15 percent and 40 percent and underlain by soils that consist largely of sand, gravel or glacial till. iii. High Landslide Hazards (LH): Areas with slopes greater than 40 percent, and areas with slopes between 15 percent and 40 percent and underlain by soils consisting largely of silt and clay. iv. Very High Landslide Hazards (LV): Areas of known mapped or identified landslide deposits.” The existing topography at the site consists of a slight slope with gradients that appear to be less than 15 percent and the site is not mapped as a steep slope by the City of Renton. Therefore, the site does not contain a sensitive or protected slope and would be classified as a Low Landslide Hazard per the RMC. April 15, 2022 Project No. T-8706 Page No. 5   3.4.4 Seismic Hazard Areas Section 4-3-050G 5.d of the RMC defines seismic hazard areas as: “i. Low Seismic Hazard (SL): Areas underlain by dense soils or bedrock. These soils generally have site classifications of A through D, as defined in the International Building Code, 2012. ii. High Seismic Hazard (SH): Areas underlain by soft or loose, saturated soils. These soils generally have site classifications E or F, as defined in the International Building Code, 2012.” Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations. Liquefaction mainly affects geologically recent deposits of fine-grained sand that is below the groundwater table. Soils of this nature derive their strength from intergranular friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction; thus, eliminating the soil’s strength. Based on the soil and groundwater conditions we observed at the site, it is our opinion that the risk for damage resulting from soil liquefication or subsidence during a severe seismic event is negligible. Therefore, in our opinion, unusual seismic hazard areas do not exist at the site and design in accordance with local building codes for determining seismic forces would adequately mitigate impacts associated with ground shaking. The site would be classified as a Low Seismic Hazard per the City of Renton. 3.4.5 Coal Mine Hazard Areas Section 4-3-050G 5.e of the RMC defines coal mine hazard areas as: “i. Low Coal Mine Hazards (CL): Areas with no known mine workings and no predicted subsidence. While no mines are known in these areas, undocumented mining is known to have occurred. ii. Medium Coal Mine Hazards (CM): Areas where mine workings are deeper than 200 feet for steeply dipping seams, or deeper than 15 times the thickness of the seam or workings for gently dipping seams. These areas may be affected by subsidence. iii. High Coal Mine Hazard (CH): Areas with abandoned and improperly sealed mine openings and areas underlain by mine workings shallower than 200 feet in depth for steeply dipping seams, or shallower than fifteen (15) times the thickness of the seam or workings for gently dipping seams. These areas may be affected by collapse or other subsidence.” Based on a review of documented mining operations in the area, there are no noted coal mines nearby. Therefore, the site would be considered a Low Coal Mine Hazard per the RMC. 3.5 Seismic Design Parameters Based on soil conditions noted in the test pits and our knowledge of the area geology, per Chapter 16 of the 2018 International Building Code (IBC), site class “D” should be used in structural design. April 15, 2022 Project No. T-8706 Page No. 6   4.0 DISCUSSION AND RECOMMENDATIONS 4.1 General Based on our study, in our opinion, the primary geotechnical concern is the approximately six to seven feet of undocumented, loose fill material in the northern portion of the site. With the proposed below grade parking, we expect excavations of 10 to 12 feet will be required to achieve building foundations. The excavation for the below grade structure is expected to remove the unsuitable material without additional over exaction required. Due to site constraints, the excavation needed to achieve the below grade parking level will likely need to be shored. With the relatively shallow excavation depths expected, we recommend using cantilevered soldier piles with timber lagging for the shoring system. The native soils observed under the fill and in the southern portion of the site would be suitable for building support. The building can be supported on conventional spread footings bearing on competent native glacial till soils, competent existing fill soils, or structural fill placed and compacted above these competent soils. Floor slabs and pavements can be similarly supported. The silty sand and silty sand with gravel soils encountered at the site contain a sufficient amount of fines such that they will be difficult to compact as structural fill when too wet. Accordingly, the ability to use the soils from site excavations as structural fill will depend on their moisture content and the prevailing weather conditions at the time of construction. If grading activities will take place during the winter season, the owner should be prepared to import free-draining granular material for use as structural fill and backfill. The following sections provide detailed recommendations regarding the preceding issues and other geotechnical design and construction considerations. These recommendations should be incorporated into the final design drawings and construction specifications. 4.2 Site Preparation and Grading To prepare the site for construction, all vegetation, organic surface soils, and other deleterious material should be stripped and removed from below the building lots and roadway areas. Surface stripping depths of approximately 4 to 12 inches should be expected to remove the organic surface soils. In the developed portions of the site, demolition of existing structures should include removal of existing foundations and abandonment of underground septic systems and other buried utilities. Abandoned utility pipes that fall outside of new building areas can be left in place provided they are sealed to prevent intrusion of groundwater seepage and soil. Organic topsoil will not be suitable for use as structural fill but may be used for limited depths in nonstructural areas. The native and existing fill soils encountered at the site contain a sufficient amount of soil fines that will make them difficult to compact as structural fill when too wet or too dry. The ability to use these soils from site excavations as structural fill will depend on its moisture content and the prevailing weather conditions at the time of construction. If wet soils are encountered, the contractor will need to dry the soils by aeration during dry weather conditions. Alternatively, the use of an additive such as Portland cement or lime to stabilize the soil moisture can be considered. If the soil is amended, additional Best Management Practices (BMPs) addressing the potential for elevated pH levels will need to be included in the Storm Water Pollution Prevention Program (SWPPP) prepared with the Temporary Erosion and Sedimentation Control (TESC) plan. April 15, 2022 Project No. T-8706 Page No. 7   If grading activities are planned during the wet winter months, or if they are initiated during the summer and extend into fall and winter, the owner should be prepared to import wet weather structural fill. For this purpose, we recommend importing a granular soil that meets the following grading requirements: U.S. Sieve Size Percent Passing 6 inches 100 No. 4 75 maximum No. 200 5 maximum* * Based on the ¾-inch fraction. Prior to use, Terra Associates, Inc. should examine and test all materials imported to the site for use as structural fill. Structural fill should be placed in uniform loose layers not exceeding 12 inches, and compacted to a minimum of 95 percent of the soil’s maximum dry density, as determined by American Society for Testing and Materials (ASTM) Test Designation D-1557 (Modified Proctor). The moisture content of the soil at the time of compaction should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the degree of compaction can be reduced to 90 percent. 4.3 Excavation, Shoring, and Dewatering Given the expected excavation depth and building limits, site constraints will likely require that the excavation sidewalls be supported by temporary shoring. As noted above, with the relatively shallow excavation, we recommend using cantilevered soldier pile walls with timber lagging. The following sections outline our recommendations for design of the temporary shoring system: Soldier Pile Shoring Cantilevered soldier pile walls should be designed to resist lateral loads imposed by the adjacent soils, building foundations, and any imposed surcharge loading. To support vertical loads, we recommend soldier piles be designed on the basis of end-bearing and pile shaft friction below the base of the excavation. Pile shaft friction above the base of the excavation should not be used to resist vertical downward loads. The following soil parameters can be used for design:  Bearing materials: very dense silty sand with gravel  Minimum depth of embedment below excavation base: 10 feet  Allowable end-bearing capacities for soldier piles: 18 kips per square foot (ksf)  Skin friction below excavation base: 2.0 ksf April 15, 2022 Project No. T-8706 Page No. 8   We recommend soldier piles have a maximum center-to-center spacing of 8 feet. Recommended design earth pressure diagrams are presented on Figure 3. For pile spacing of 8 feet and less, the lateral soil pressure uniformly distributed over the width of the lagging can be reduced by 50 percent to account for soil arching between the soldier piles. Unshored excavation heights within the very dense native soils should not exceed five feet. Within the upper medium dense silty sand soils unshored excavation heights should not exceed three feet. No excavations should remain unsupported for more than 24 hours. In addition, the contractor must be prepared to case the upper portion of the drilled shafts to prevent collapse and maintain a relatively clean, open hole. Due to the nature of the shoring system, the shaft bottoms must be relatively clean of loose soil debris prior to insertion of the soldier pile beam and pouring concrete. Over-break or gaps between the excavated soil face and the back of the lagging must be filled following each excavation lift. Filling with crushed rock, suitable native soils, or grouting with control density fill (CDF) is recommended. This will be an important consideration in limiting movement of the adjacent ground. Dewatering Based on the expected excavation depths and the groundwater conditions observed at the test pits, active dewatering will likely not be required to facilitate construction. Conventional trenches and sump pumps should be sufficient to control the water during construction. Although not anticipated, additional dewatering techniques may be required to control the flow during construction, particularly if construction takes place in the wet winter months when perched groundwater has a chance to be encountered. Monitoring Program A monitoring program must be implemented to verify the performance of the shoring system and possible excavation effects on adjacent properties. The first step of this program should consist of documenting the existing conditions of the adjacent properties and pavements. The documentation should include a visual survey and a pictorial record. We recommend optical survey monitoring be conducted by the owner and include the measurement of horizontal and vertical movements of: 1. The short retaining wall along the eastern property boundary. 2. The adjacent buildings to the west and north. 3. The shoring system. To monitor potential vertical and horizontal movements of the shoring, monitoring points should be established at the top of every other soldier pile. When the excavation reaches the halfway point, depending on readings obtained during the initial excavation phase, additional monitoring points may need to be established. Surface reference points should be established and monitored for elevation at distances of 5 and 10 feet from the back of the shoring at spacing of 25 feet at the excavation perimeter. April 15, 2022 Project No. T-8706 Page No. 9   Optical monitoring of the shoring system should be performed twice a week as the excavation proceeds and then every other week upon completion of the excavation. A registered land surveyor should be retained to perform the monitoring. Monitoring should continue until the basement/parking garage walls are adequately braced at the ground surface level. The monitoring data should be submitted within one day to the project shoring designer and Terra Associates, Inc. for review. General Excavations Aside from deeper shoring excavations for the below-grade level, the remaining excavations at the site associated with confined spaces, such as utility trenches, must be completed in accordance with local, state, or federal requirements. Based on current Washington Industrial Safety and Health Act (WISHA) regulations, the upper loose to medium dense soils would be classified as Type C soil. The deeper dense to very dense glacial till soils would be classified as Type A soil. Accordingly, temporary excavations in Type C soils should have their slopes laid back at an inclination of 1.5:1 (Horizontal:Vertical) or flatter, from the toe to the crest of the slope. Side slopes in Type A soils can be laid back at a slope inclination of 0.75:1 or flatter. For temporary excavation slopes less than 8 feet in height in Type A soils, the lower 3.5 feet can be cut to a vertical condition, with a 0.75:1 slope graded above. For temporary excavation slopes greater than 8 feet in height up to a maximum height of 12 feet, the slope above the 3.5-foot vertical portion will need to be laid back at a minimum slope inclination of 1:1. No vertical cut with a backslope immediately above is allowed for excavation depths that exceed 12 feet. In this case, a four-foot vertical cut with an equivalent horizontal bench to the cut slope toe is required. All exposed temporary slope faces that will remain open for an extended period of time should be covered with a durable reinforced plastic membrane during construction to prevent slope raveling and rutting during periods of precipitation. This information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It is understood that job site safety is the sole responsibility of the project contractor. 4.4 Foundation Support The building may be supported on conventional isolated or continuous footing foundations bearing on competent native soils. Perimeter foundations exposed to the weather should be at a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. Based on the anticipated below-grade parking level and an excavation of 10 feet or more, we recommend designing foundations supported on native soils for a net allowable bearing capacity of 5,000 pounds per square foot. For short-term loads, such as wind and seismic, a one-third increase in this allowable capacity can be used. With the anticipated building loads and this bearing stress applied to the soil, we estimate total foundation settlement on the native soils would not exceed one inch. April 15, 2022 Project No. T-8706 Page No. 10   For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth pressures acting on the side of the footing can also be considered. We recommend calculating this lateral resistance using an equivalent fluid weight of 350 pounds per cubic foot (pcf). We recommend not including the upper 12 inches of soil in this computation because it can be affected by weather or disturbed by future grading activity. This value assumes the foundation will be constructed neat against competent native soil or backfilled with structural fill as described in Section 4.2 of this report. The values recommended include a safety factor of 1.5. The native soils observed in our test pits will be subject to disturbance from normal construction activity when wet. If disturbed, the soils will not be suitable for foundation support and would need to be removed to expose undisturbed soils. To avoid soil disturbance, protection of the bearing subgrade with a layer of lean mix concrete should be considered. 4.5 Floor Slab-on-Grade Slab-on-grade floors may be supported on competent, undisturbed, bearing surfaces consisting of competent native soils. Immediately below the floor slab, we recommend placing a four-inch-thick capillary break layer composed of clean, coarse sand or fine gravel that has less than five percent passing the No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. The capillary break layer will not prevent moisture intrusion through the slab caused by water vapor transmission. Where moisture by vapor transmission is undesirable, such as covered floor areas, a common practice is to place a durable plastic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or fine gravel to protect it from damage during construction, and to aid in uniform curing of the concrete slab. It should be noted that if the sand or gravel layer overlying the membrane is saturated prior to pouring the slab, it will not be effective in assisting uniform curing of the slab and can actually serve as a water supply for moisture bleeding through the slab, potentially affecting floor coverings. Therefore, in our opinion, covering the membrane with a layer of sand or gravel should be avoided if floor slab construction occurs during the wet winter months and the layer cannot be effectively drained. We recommend floor designers and contractors refer to the current American Concrete Institute (ACI) Manual of Concrete Practice for further information regarding vapor barrier installation below slab-on-grade floors. 4.6 Lateral Earth Pressures Lower-level building walls should be designed for earth pressure parameters presented on Figure 4. To prevent hydrostatic loading, the walls must be provided with adequate drainage. Typically, for walls constructed against temporary soldier pile/timber lagging, wall drainage is provided by attaching prefabricated drainage panels, such as Miradrain G100N, to the shoring. Drainpipes are attached to the Miradrain panels at the wall base and tightlined to discharge through the permanent wall. A typical drainage detail for permanent lower-level walls constructed against the temporary shoring system is shown on Figure 5. April 15, 2022 Project No. T-8706 Page No. 11   4.7 Stormwater Facilities It is our understanding that site stormwater is planned to be directed to a below-grade vault located at the southern extent of the property. Detention Vault Based on the anticipated southern limit location of the vault, we expect that the bottom of the excavation would expose native, dense silty sand with gravel soils. Vault foundations supported by these native soils may be designed for an allowable bearing capacity of 5,000 psf provided that the foundation subgrade is at least eight feet below current grades. For short-term loads, such as seismic, a one-third increase in this allowable capacity can be used. Vault walls should be designed as below-grade retaining walls. The magnitude of earth pressure development on engineered retaining walls will partly depend on the quality of the wall backfill. We recommend placing and compacting wall backfill as structural fill as described in Section 4.2 of this report. To prevent overstressing the walls during backfilling, heavy construction machinery should not be operated within five feet of the wall. Wall backfill in this zone should be compacted with hand-operated equipment. To prevent hydrostatic pressure development, wall drainage must also be installed. A typical drainage detail is shown on Figure 6. With wall backfill placed and compacted as recommended and drainage properly installed, we recommend designing unrestrained walls for an active earth pressure equivalent to a fluid weighing 35 pounds per cubic foot (pcf). For restrained walls, an additional uniform load of 100 pounds per square foot (psf) should be added to the 35 pcf. To account for typical traffic surcharge loading, the walls can be designed for an additional imaginary height of two feet (two-foot soil surcharge). For evaluation of below-grade walls under seismic loading, an additional uniform lateral pressure equivalent to 8H psf, where H is the height of the below-grade portion of the wall in feet, can be used. These values assume a horizontal backfill condition and that no other surcharge loading such as traffic, sloping embankments, or adjacent buildings will act on the wall. If such conditions will exist, then the imposed loading must be included in the wall design. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are given in Section 4.4 of this report. If it is not possible to discharge collected water at the footing invert elevation, the invert elevation of the drainpipe could be set equivalent to the outfall invert. For any portion of the wall that falls below the invert elevation of the wall drain, an earth pressure equivalent to a fluid weighing 85 pcf should be used. We should review the stormwater plans when they are completed and revise our recommendations, if required. April 15, 2022 Project No. T-8706 Page No. 12   4.8 Infiltration Feasibility The soils at this site generally consist of silty sand glacial till soils that would impede the downward migration of any site stormwater. Based on the soil conditions observed, it is our opinion that the on-site soils are not suitable for support of large-scale or low impact development (LID) infiltration facilities. 4.9 Drainage Surface Final exterior grades should promote free and positive drainage away from the site at all times. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building areas. We recommend providing a positive drainage gradient away from the building perimeters. If this gradient cannot be provided, surface water should be collected adjacent to the structures and disposed to appropriate storm facilities. Subsurface We recommend installing perimeter foundation drains adjacent to shallow foundations. The drains can be laid to grade at an invert elevation equivalent to the bottom of footing grade. The drains can consist of four-inch diameter perforated PVC pipe that is enveloped in washed pea gravel-sized drainage aggregate. The aggregate should extend six inches above and to the sides of the pipe. Roof and foundation drains should be tightlined separately to the storm drains. All drains should be provided with cleanouts at easily accessible locations. 4.10 Utilities Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) or the local jurisdiction’s specifications. As a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 4.2 of this report. As noted, depending on the soil moisture when excavated most inorganic native and existing fill soils on the site should be suitable for use as backfill material during dry weather conditions. However, if utility construction takes place during the wet winter months, it will likely be necessary to import suitable wet weather fill for utility trench backfilling. 4.11 Pavement Pavement subgrades should be prepared as described in the Section 4.2 of this report. Regardless of the degree of relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. The subgrade should be proofrolled with heavy rubber-tire construction equipment such as a loaded 10-yard dump truck to verify this condition. April 15, 2022 Project No. T-8706 Page No. 13   The pavement design section is dependent upon the supporting capability of the subgrade soils and the traffic conditions to which it will be subjected. We expect traffic will mainly consist of light passenger and commercial vehicles with only occasional heavy traffic in the form of moving trucks and trash removal vehicles. Based on this information, with a stable subgrade prepared as recommended, we recommend the following pavement sections:  Two inches of hot mix asphalt (HMA) over four inches of crushed rock base (CRB)  Three and one-half inches full depth HMA All paving materials should conform to Washington State Department of Transportation (WSDOT) specifications for HMA and CRB. Long-term pavement performance will depend on surface drainage. A poorly drained pavement section will be subject to premature failure as a result of surface water infiltrating into the subgrade soils and reducing their supporting capability. For optimum performance, we recommend surface drainage gradients of at least two percent. Some degree of longitudinal and transverse cracking of the pavement surface should be expected over time. Regular maintenance should be planned to seal cracks when they occur. 5.0 ADDITIONAL SERVICES Terra Associates, Inc. should review the final design drawings and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and implemented in project design. We should also provide geotechnical service during construction to observe compliance with our design concepts, specifications, and recommendations. This will allow for design changes if subsurface conditions differ from those anticipated prior to the start of construction. 6.0 LIMITATIONS We prepared this report in accordance with generally accepted geotechnical engineering practices. No other warranty, expressed or implied, is made. This report is the copyrighted property of Terra Associates, Inc. and is intended for specific application to the Vision House Children’s Village project in Renton, Washington. This report is for the exclusive use of Pavillon, LLC and their authorized representatives. The analyses and recommendations present in this report are based on data obtained from the subsurface explorations completed onsite. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. © 2022 Microsoft Corporation © 2022 TomTom SITE Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and Figure 1 VICINITY MAP 0 1000 2000 APPROXIMATE SCALE IN FEET REFERENCE: https://www.bing.com/maps ACCESSED 3/17/2022 Proj.No. T-8706 Date: APR 2022 RENTON, WASHINGTON VISION HOUSE CHILDREN'S VILLAGE © 2022 Microsoft Corporation © 2022 Maxar ©CNES (2022) Distribution Airbus DS © 2022 TomTom TP-1 TP-2 TP-3 TP-4 REFERENCE: REFERENCE ONLY AND SHOULD NOT BE USED FOR DESIGN OR CONSTRUCTION PURPOSES. DIMENSIONS ARE APPROXIMATE. IT IS INTENDED FOR NOTE: THIS SITE PLAN IS SCHEMATIC. ALL LOCATIONS AND LEGEND: 0 50 100 APPROXIMATE SCALE IN FEETSITE PLAN PROVIDED BY BING MAPS. APPROXIMATE TEST PIT LOCATION Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and EXPLORATION LOCATION PLAN Figure 2Proj.No. T-8706 Date: APR 2022 RENTON, WASHINGTON VISION HOUSE CHILDREN'S VILLAGE 12" COMPACTED STRUCTURAL FILL EXCAVATED SLOPE (SEE REPORT TEXT FOR APPROPRIATE INCLINATIONS) SLOPE TO DRAIN 12" MINIMUM 3/4" MINUS WASHED GRAVEL 3" BELOW PIPE 12" OVER PIPE 4" DIAMETER PERFORATED PVC PIPE SEE NOTE 6"(MIN.) NOT TO SCALE NOTE: MIRADRAIN G100N PREFABRICATED DRAINAGE PANELS OR SIMILAR PRODUCT CAN BE SUBSTITUTED FOR THE 12-INCH WIDE GRAVEL DRAIN BEHIND WALL. DRAINAGE PANELS SHOULD EXTEND A MINIMUM OF SIX INCHES INTO 12-INCH THICK DRAINAGE GRAVEL LAYER OVER PERFORATED DRAIN PIPE. Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and TYPICAL WALL DRAINAGE DETAIL Figure 3Proj.No. T-8706 Date: APR 2022 RENTON, WASHINGTON VISION HOUSE CHILDREN'S VILLAGE   Project No. T-8706 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING Vision House Children’s Village Renton, Washington We explored subsurface conditions at the site by excavating 4 test pits to maximum depths of about 8 to 11 feet below existing surface grades using a mini track-mounted excavator. The test pit locations were approximately determined in the field by pacing and sighting from existing site features. The approximate test pit locations are shown on Figure 2. The Test Pit Logs are presented on Figures A-2 through A-5. A geotechnical engineer from our office conducted the field exploration, classified the soil conditions encountered, maintained a log of each test pit, obtained representative soil samples, observed pertinent site features, and performed geologic reconnaissance of the site. All soil samples were visually classified in the field in accordance with the Unified Soil Classification System (USCS) described on Figure A-1. Representative soil samples obtained from the test pits were placed in closed containers and taken to our laboratory for further examination and testing. The moisture content of each sample was measured and is reported on the Test Pit Logs. Grain size analyses were performed on select samples. The results are shown on Figures A-6. Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and MAJOR DIVISIONS LETTER SYMBOL TYPICAL DESCRIPTION GRAVELS More than 50% of coarse fraction is larger than No. 4 sieve Clean Gravels (less than 5% fines) GW Well-graded gravels, gravel-sand mixtures, little or no fines. GP Poorly-graded gravels, gravel-sand mixtures, little or no fines. Gravels with fines GM Silty gravels, gravel-sand-silt mixtures, non-plastic fines. GC Clayey gravels, gravel-sand-clay mixtures, plastic fines. SANDS More than 50% of coarse fraction is smaller than No. 4 sieve Clean Sands (less than 5% fines) SW Well-graded sands, sands with gravel, little or no fines. SP Poorly-graded sands, sands with gravel, little or no fines. Sands with fines SM Silty sands, sand-silt mixtures, non-plastic fines. SC Clayey sands, sand-clay mixtures, plastic fines. SILTS AND CLAYS Liquid Limit is less than 50% ML Inorganic silts, rock flour, clayey silts with slight plasticity. CL Inorganic clays of low to medium plasticity. (Lean clay) OL Organic silts and organic clays of low plasticity. SILTS AND CLAYS Liquid Limit is greater than 50% MH Inorganic silts, elastic. CH Inorganic clays of high plasticity. (Fat clay) OH Organic clays of high plasticity. HIGHLY ORGANIC SOILS PT Peat. CO A R S E G R A I N E D S O I L S Mo r e t h a n 5 0 % m a t e r i a l l a r g e r th a n N o . 2 0 0 s i e v e s i z e FI N E G R A I N E D S O I L S Mo r e t h a n 5 0 % m a t e r i a l s m a l l e r th a n N o . 2 0 0 s i e v e s i z e DEFINITION OF TERMS AND SYMBOLS CO H E S I O N L E S S CO H E S I V E Standard Penetration Density Resistance in Blows/Foot Very Loose 0-4 Loose 4-10 Medium Dense 10-30 Dense 30-50 Very Dense >50 Standard Penetration Consistancy Resistance in Blows/Foot Very Soft 0-2 Soft 2-4 Medium Stiff 4-8 Stiff 8-16 Very Stiff 16-32 Hard >32 2" OUTSIDE DIAMETER SPILT SPOON SAMPLER 2.4" INSIDE DIAMETER RING SAMPLER OR SHELBY TUBE SAMPLER WATER LEVEL (Date) Tr TORVANE READINGS, tsf Pp PENETROMETER READING, tsf DD DRY DENSITY, pounds per cubic foot LL LIQUID LIMIT, percent PI PLASTIC INDEX N STANDARD PENETRATION, blows per foot UNIFIED SOIL CLASSIFICATION SYSTEM Figure A-1Proj.No. T-8706 Date: APR 2022 RENTON, WASHINGTON VISION HOUSE CHILDREN'S VILLAGE Sa m p l e N o . De p t h ( f t ) PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W ( % ) interpreted as being indicative of other locations at the site. NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 A-2 T-8706 SLK Renton, Washington Grass Februrary 7, 2022 Vision House Children's Village LOG OF TEST PIT NO. TP-1 N/A N/A 1.5 to 6 feet 10.8 14.2 9.3 Medium Dense Loose Dense (4 inches SOD) FILL: Light brown silty SAND with gravel, fine sand, fine to coarse gravel, moist, scattered roots. (SM) FILL: Dark brown silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, scattered cobbles, some plastic and wood debris. (SM) Red/brown silty SAND, fine to coarse sand, moist, some fine gravel. (SM) (Weathered Till) Gray silty SAND with gravel, fine to medium sand, fine gravel, moist. (SM) (Till) Test Pit terminated at approximately 9 feet. Heavy caving observed from 1.5 to 6 feet. No seepage observed. Sa m p l e N o . De p t h ( f t ) PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W ( % ) interpreted as being indicative of other locations at the site. NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 11 12 13 A-3 T-8706 SLK Renton, Washington Grass Februrary 7, 2022 Vision House Children's Village LOG OF TEST PIT NO. TP-2 N/A N/A 0.5 to 3 feet 12.8 10.3 Medium Dense Loose to Medium Dense Medium Dense Dense (5 inches SOD) FILL: Dark brown silty SAND/sandy SILT with gravel, fine sand, fine to coarse gravel, moist, heavy root inclusions. (SM/ML) (Topsoil) FILL: Dark brown/red silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, cobbles, scattered roots, some concrete, brick and wood debris, trace glass debris. (SM) FILL (?): Red/brown silty SAND with gravel, fine to medium sand, fine gravel, moist, trace cobbles and roots. (SM) Red/brown silty SAND with gravel, fine to medium sand, fine gravel, moist. (SM) (Weathered Till) Gray silty SAND with gravel, fine to medium sand, fine gravel, moist. (SM) (Till) Test Pit terminated at approximately 11 feet. Light caving observed from 0.5 to 3 feet. No seepage observed. Sa m p l e N o . De p t h ( f t ) PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W ( % ) interpreted as being indicative of other locations at the site. NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 A-4 T-8706 SLK Renton, Washington Blackberry Bushes Februrary 7, 2022 Vision House Children's Village LOG OF TEST PIT NO. TP-3 N/A N/A N/A 11.2 9.6 Loose Dense Very Dense Dark brown silty SAND with gravel, fine sand, fine to coarse gravel, moist, heavy root inclusions. (SM) (Topsoil) Gray silty SAND with gravel, fine to medium sand, fine gravel, moist. (SM) (Till) Test Pit terminated at approximately 8 feet. No caving observed. No seepage observed. Sa m p l e N o . De p t h ( f t ) PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W ( % ) interpreted as being indicative of other locations at the site. NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 A-5 T-8706 SLK Renton, Washington Grass Februrary 7, 2022 Vision House Children's Village LOG OF TEST PIT NO. TP-4 N/A N/A N/A 11.2 9.6 Loose Dense Very Dense Medium Dense (1-inch SOD) FILL: Dark brown silty SAND with gravel, fine sand, fine to coarse gravel, moist, heavy root inclusions. (SM) (Topsoil) FILL (?): Red/brown silty SAND with gravel, fine to medium sand, fine gravel, moist, trace cobbles and roots. (SM) Gray silty SAND with gravel, fine to medium sand, fine gravel, moist. (SM) (Till) Test Pit terminated at approximately 8 feet. No caving observed. No seepage observed. Tested By: FQ LL PL D85 D60 D50 D30 D15 D10 Cc Cu Material Description USCS AASHTO Project No.Client:Remarks: Project: Location: TP-1 Depth: -6 feet Location: TP-2 Depth: -7 feet Location: TP-3 Depth: -5 feet Terra Associates, Inc. Kirkland, WA Figure 4.2629 0.4414 0.2811 0.1064 14.0034 4.4918 2.1980 0.2953 0.0795 10.3493 1.2992 0.4459 0.1417 silty SAND SM silty SAND with gravel SM silty SAND with gravel SM T-8706 Pavillon, LLC A-6 PE R C E N T F I N E R 0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % +3"Coarse % Gravel Fine Coarse Medium % Sand Fine Silt % Fines Clay 0.0 0.0 13.4 11.3 16.0 35.3 24.0 0.0 6.5 32.7 11.9 13.1 21.3 14.5 0.0 0.0 24.3 10.9 15.5 29.2 20.1 6 i n . 3 i n . 2 i n . 1½ i n . 1 i n . ¾ i n . ½ i n . 3/ 8 i n . #4 #1 0 #2 0 #3 0 #4 0 #6 0 #1 0 0 #1 4 0 #2 0 0 Particle Size Distribution Report Vision House Children's Village Tested on Februrary 22, 2022 Tested on Februrary 22, 2022 Tested on Februrary 22, 2022