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HomeMy WebLinkAboutExh.07_Geotech_Report Geotechnical Investigation Proposed Residential Development 122xx SE Petrovitsky Road Renton, Washington June 17, 2019 EXHIBIT 7 DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON i Table of Contents 1.0 INTRODUCTION ............................................................................................................. 1 2.0 PROJECT DESCRIPTION .............................................................................................. 1 3.0 SITE DESCRIPTION ....................................................................................................... 1 4.0 FIELD INVESTIGATION ............................................................................................... 1 4.1.1 Site Investigation Program ................................................................................... 1 5.0 SOIL AND GROUNDWATER CONDITIONS .............................................................. 2 5.1.1 Area Geology ........................................................................................................ 2 5.1.2 Groundwater ........................................................................................................ 2 6.0 GEOLOGIC HAZARDS ................................................................................................... 3 6.1 Erosion Hazard .................................................................................................... 3 6.2 Seismic Hazard .................................................................................................... 3 7.0 DISCUSSION ................................................................................................................... 3 7.1.1 General................................................................................................................. 3 8.0 RECOMMENDATIONS .................................................................................................. 4 8.1.1 Site Preparation ................................................................................................... 4 8.1.2 Temporary Excavations ........................................................................................ 4 8.1.3 Erosion and Sediment Control.............................................................................. 5 8.1.4 Foundation Design ............................................................................................... 5 8.1.5 Stormwater Management ..................................................................................... 6 8.1.6 Slab-on-Grade ...................................................................................................... 7 8.1.7 Groundwater Influence on Construction .............................................................. 7 8.1.8 Utilities ................................................................................................................ 7 8.1.9 Pavements ............................................................................................................ 9 9.0 CONSTRUCTION FIELD REVIEWS ............................................................................ 9 10.0 CLOSURE ...................................................................................................................10 LIST OF APPENDICES Appendix A — Statement of General Conditions Appendix B — Figures Appendix C — Test Pit Logs DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 1 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 1.0 Introduction In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical investigation for the proposed residential development located at 122xx SE Petrovitsky Road in Renton, Washington (Figure 1). The purpose of the geotechnical investigation was to identify subsurface conditions and to provide geotechnical recommendations for foundation design, stormwater management, earthwork, soil compaction, and suitability of the on-site soils for use as fill. The scope of work for the geotechnical evaluation consisted of a site investigation followed by engineering analyses to prepare this report. Recommendations presented herein pertain to various geotechn ical aspects of the proposed development, including foundation support of the new buildings and new pavements. 2.0 Project Description The project includes construction of two multi-story, multi-unit residential buildings in the southern portion of the property. The buildings will have six units (north) and five units (north) for a total of 11 residential units. Parking areas will be located along the east property line and a drive lane will extend into the property and between the buildings from the west. Anticipated building loads are expected to be light to moderate and site grading will include cuts and fills on the order of 4 feet or less. Stormwater management will include infiltration devices, if feasible. We should be provided with the final plans when they become available. 3.0 Site Description The site is located at 122xx SE Petrovitsky Road in Renton, Washington (Figure 1). The property consists of one irregularly shaped parcel (No. 0739000050) with a total area of about 33,542 square feet. The site is undeveloped and vegetated with grasses, ferns, ivy, blackberry vines, Scotch Broom, and variable diameter deciduous trees. The site slopes gently downward from north to south at magnitudes of less than 10 percent and relief of about 8 feet. The site is bordered to the east, west, and north by commercial and residential developments and to the south by SE Petrovitsky Road. 4.0 Field Investigation 4.1.1 Site Investigation Program The geotechnical field investigation program was completed on May 30, 2019 and included excavating and sampling four test pits within the property for subsurface analysis. DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 2 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 The soils encountered were logged in the field and are described in accordance with the Unified Soil Classification System (USCS). A Cobalt Geosciences field representative conducted the explorations, collected disturbed soil samples, classified the encountered soils, kept a detailed log of the explorations, and observed and recorded pertinent site features. The results of the sampling are presented on the exploration logs enclosed in Appendix C. 5.0 Soil and Groundwater Conditions 5.1.1 Area Geology The site lies within the Puget Lowland. The lowland is part of a regional north-south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington, this lowland is glacially carved, with a depositional and erosional history including at least four separate glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to the east by the Cascade Range. The lowland is filled with glacial and non -glacial sediments consisting of interbedded gravel, sand, silt, till, and peat lenses. The Geologic Map of King County, indicates that the site is underlain by Vashon Glacial Till. Vashon Glacial Till is typically characterized by an unsorted, non -stratified mixture of clay, silt, sand, gravel, cobbles and boulders in variable quantities. These materials are typically dense and relatively impermeable. The poor sorting reflects the mixing of the materials as these sediments were overridden and incorporated by the glacial ice. Explorations The test pits encountered 6 to 12 inches of topsoil and vegetation underlain by approximately 3.5 to 5.5 feet of loose to medium dense, silty-fine to medium grained sand with gravel (Fill and/or Weathered Glacial Till). These materials were underlain by dense to very dense, silty-fine to medium grained sand with gravel (Glacial Till), which continued to the termination depth of the explorations. 5.1.2 Groundwater Groundwater was not encountered in any of the explorations. There is a chance that perched groundwater may be encountered during late winter and early spring months. We anticipate that groundwater would be perched between fill or weathered till and underlying unweathered glacial till. Depths to groundwater would vary from about 3 to 6 feet below grades. Water table elevations often fluctuate over time. The groundwat er level will depend on a variety of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability. Water levels at the time of the field investigation may be different from those encountered during the construction phase of the project. DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 3 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 6.0 Geologic Hazards 6.1 Erosion Hazard The Natural Resources Conservation Services (NRCS) maps for King County indicate that the site is underlain by Alderwood gravelly sandy loam (8 to 15 percent slopes). These soils would have a slight to moderate erosion potential in a disturbed state, depending on the slope magnitude. It is our opinion that soil erosion potential at this project site can be reduced through landscaping and surface water runoff control. Typically erosion of exposed soils will be most noticeable during periods of rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The t ypical wet weather season, with regard to site grading, is from October 31st to April 1st. Erosion control measures should be in place before the onset of wet weather. 6.2 Seismic Hazard The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the 2015 International Building Code (2015 IBC). A Site Class D applies to an overall profile consisting of dense to very dense soils within the upper 100 feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for SS, S1, Fa, and Fv. The USGS website includes the most updated published data on seismic conditions. The site specific seismic design parameters and adjusted maximum spectral response acceleration parameters are as follows: PGA (Peak Ground Acceleration, in percent of g) SS 138.10% of g S1 51.50% of g FA 1.00 FV 1.50 Additional seismic considerations include liquefaction potential and amplification of ground motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table. The relatively dense soil deposits that underlie the site have a low liquefaction potential. 7.0 DISCUSSION 7.1.1 General The site is underlain by areas of fill along with weathered and unweathered glacial till. The proposed residential buildings may be supported on shallow foundation systems bearing on medium dense or firmer native soils and/or structural fill placed on suitable native soils. Local overexcavation of fill and/or loose soils may be necessary below proposed foundation elements. DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 4 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 We recommend utilizing dispersion devices (if feasible based on space), detention, permeable pavements, or rain gardens for stormwater management. The shallow soils are fine-grained and do not allow for widespread infiltration. 8.0 Recommendations 8.1.1 Site Preparation Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil and fill. Based on observations from the site investigation pro gram, it is anticipated that the stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below large trees and in any areas underlain by undocumented fill materials. The native soils consist of silty-sand with gravel and sandy silt with gravel. These soils may be used as structural fill provided they achieve compaction requirements and are within 3 percent of the optimum moisture. Some of these soils may only be suitable for use as fill during the summer months, as they will be above the optimum moisture levels in their current state. These soils are variably moisture sensitive and may degrade during periods of wet weather and under equipment traffic. Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of 3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the ASTM D 1557 test method. 8.1.2 Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 5 feet or less for foundation and utility placement. Excavations should be sloped no steeper than 1H:1V in medium dense native soils. If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 1.5H:1V, where room permits. Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a qualified person during construction activities and the inspections should be documented in daily reports. The contractor is responsible for maintaining the stability of the temporary cut slopes and reducing slope erosion during construction. Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, and the slopes should be closely monitored until the permanent retaining systems or slope configurations are complete. Materials should not be stored or equipment operated within 10 feet of the top of any temporary cut slope. Soil conditions may not be completely known from the geotechnical investigation. In the case of temporary cuts, the existing soil conditions may not be completely revealed until the excavation work exposes the soil. Typically, as excavation work progresses the maximum inclination of temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental recommendations can be DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 5 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 made. Soil and groundwater conditions can be highly variable. Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that the project can proceed and required deadlines can be met. If any variations or undesirable conditions are encountered during construction, we should be notified so that supplemental recommendations can be made. If room constraints or groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring systems may be required. The contractor should be responsible for developin g temporary shoring systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review temporary shoring designs prior to installation, to verify the suitability of the proposed systems. 8.1.3 Erosion and Sediment Control Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures should be implemented and these measures should be in general accordance with local regulations. At a minimum, the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site:  Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the site soils, to take place during the dry season (generally May through September). However, provided precautions are taken using Best Management Practices (BMP’s), grading activities can be completed during the wet season (generally October through April).  All site work should be completed and stabilized as quickly as possible.  Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences, silt fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration systems.  Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. 8.1.4 Foundation Design The proposed residential buildings may be supported on shallow spread footing foundation systems bearing on undisturbed medium dense or firmer native soils or on properly compacted structural fill placed on the suitable native soils. If structural fill is used to support foundations, then the zone of structural fill should extend beyond the faces of the footing a lateral distance at least equal to the thickness of the structural fill. Depending on the location and finish floor elevations of new residences, some overexcavation may be required. Any fill will need to be removed below new footings and replaced with compacted structural fill as discussed above. For shallow foundation support, we recommend widths of at least 18 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed structure. Provided that the DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 6 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 footings are supported as recommended above, a net allowable bearing pressure of 3,000 pounds per square foot (psf) may be used for design. A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing exca vations should be inspected to verify that the foundations will bear on suitable material. Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch. Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings, should be less than ½ inch. This translates to an angular distortion of 0.002. Most settlement is expected to occur during construction, as the loads are applied. However, additional post -construction settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be observed by a qualified geotechnical consultant. Resistance to lateral footing displacement can be determined using an allowable friction fact or of 0.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can also be developed using an allowable equivalent fluid passive pressure of 275 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior areas). The allowable friction factor and allowable equivalent fluid passive pressure values include a factor of safety of 1.5. The frictional and passive resistance of the soil m ay be combined without reduction in determining the total lateral resistance. A 1/3 increase in the above values may be used for short duration transient loads. Care should be taken to prevent wetting or drying of the bearing materials during construction. Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing excavations, should be removed prior to placing concrete. The potential for wetting or drying of the bearing materials can be reduced by pouring concret e as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. 8.1.5 Stormwater Management It is our opinion that infiltration of stormwater runoff utilizing trenches or drywells is not feasible due to the underlying soil conditions and likely groundwater conditions during the wet season. We performed a small-scale pilot infiltration test in TP-1 at a depth of 4 feet below grade. Following testing a nd application of correction factors for testing (0.5), site variability (0.33), and influent control (0.9), the infiltration rate was found to be 0.18 inches per hour. This is lower than what is considered feasible by the Washington State Department of Ecology. It may be feasible to utilize dispersion trenches with vegetated flowpaths for a portion of runoff from new impervious surfaces. Additional options for management include detention vaults, rain gardens, and permeable pavements for flow control. DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 7 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 We should be provided with the final stormwater plans to verify suitability of the location, type, and depth of any on-site management system. These recommendations should be considered preliminary and for discussion until the final design has been determined. We can update these recommendations and/or provide additional recommendations once an overall stormwater management plan has been developed. 8.1.6 Slab-on-Grade We recommend that the upper 12 inches of the existing fill and/or native soils within slab areas be re- compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could result in curling of the concrete slab at joints. Floo r covers sensitive to moisture typically requires the usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers. The American Concrete Institutes ACI 360R-06 Design of Slabs on Grade and ACI 302.1R-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. Slabs on grade may be designed using a coefficient of subgrade reaction of 180 pounds per cubic inch (pci) assuming the slab-on-grade base course is underlain by structural fill placed and compacted as outlined in Section 8.1. A minimum 6 inch thickness of pea gravel or 5/8 inch clean angular rock should be placed over the subgrade as a capillary break. A perimeter drainage system is recommended unless interior slab areas are elevated a minimum of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4 inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perime ter drainage system should discharge by gravity flow to a suitable stormwater system. Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface water flow away from the building and preferably with a relatively impermeable surface cover immediately adjacent to the building. 8.1.7 Groundwater Influence on Construction Groundwater was not encountered in any of the explorations. We anticipate that perched groundwater could be encountered during construction if the work takes place during late winter to early spring. Any groundwater would be light in volume and likely within 3 to 6 feet of the ground surface. If groundwater is encountered, we anticipate that sump excavations and small diameter pumps systems will adequately de-water short-term excavations, if required. Any system should be designed by the contractor. We can provide additional recommendations upon request. 8.1.8 Utilities Utility trenches should be excavated according to accepted engineering practices following OSHA (Occupational Safety and Health Administration) standards, by a contractor experienced in such work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 8 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided. Depending upon the location and depth of some utility trenches, groundwater flow into open excavations could be experienced, especially during or shortly following periods of precipitation. In general, silty soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and density and will have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet deep. All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill placed in pavement areas should be compacted to at lea st 95 percent of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe manufacturer's recommendations. The contractor is responsible for removing all water-sensitive soils from the trenches regardless of the backfill location and compaction requirements. Depending on the depth and location of th e proposed utilities, we anticipate the need to re-compact existing fill soils below the utility structures and pipes. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction procedures. 8.1.9 Pavement Recommendations The near surface subgrade soils generally consist of silty sand with gravel and areas of sandy silt with gravel. These soils are rated as good for pavement subgrade material (depending on silt content and moisture conditions). We estimate that the subgrade will have a California Bearing Ratio (CBR) value of 10 and a modulus of subgrade reaction value of k = 200 pci, provided the subgrade is prepared in general accordance with our recommendations. We recommend that at a minimum, 12 inches of the existing subgrade material be moisture conditioned (as necessary) and re-compacted to prepare for the construction of pav ement sections. Deeper levels of recompaction or overexcavation and replacement may be necessary in areas where fill and/or very poor (soft/loose) soils are present. Any soils that cannot be compacted to required levels and soils that have more than 40 percent fines by weight should be removed and replaced with imported structural fill. The subgrade should be compacted to at least 95 percent of the maximum dry density as determined by ASTM Test Method D1557. In place density tests should be performed to verify proper moisture content and adequate compaction. The recommended flexible and rigid pavement sections are based on design CBR and modulus of subgrade reaction (k) values that are achieved, only following proper subgrade preparation. It should be noted that subgrade soils that have relatively high silt contents will likely be highly sensitive to moisture conditions. The subgrade strength and performance characteristics of a silty subgrade material may be dramatically reduced if this material becomes wet. DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 9 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 Based on our knowledge of the proposed project, we expect the traffic to range from light duty (passenger automobiles) to heavy duty (delivery trucks). The following tables show the recommended pavement sections for light duty and heavy duty use. ASPHALTIC CONCRETE (FLEXIBLE) PAVEMENT LIGHT DUTY Asphaltic Concrete Aggregate Base* Compacted Subgrade* ** 2.5 in. 6.0 in. 12.0 in. HEAVY DUTY Asphaltic Concrete Aggregate Base* Compacted Subgrade* ** 3.5 in. 6.0 in. 12.0 in. PORTLAND CEMENT CONCRETE (RIGID) PAVEMENT Min. PCC Depth Aggregate Base* Compacted Subgrade* ** 6.0 in. 6.0 in. 12.0 in. * 95% compaction based on ASTM Test Method D1557 ** A proof roll may be performed in lieu of in place density tests The asphaltic concrete depth in the flexible pavement tables should be a surface course type asphalt, such as Washington Department of Transportation (WSDOT) ½ inch HMA. The rigid pavement design is based on a Portland Cement Concrete (PCC) mix that has a 28 day compressive strength of 4,000 pounds per square inch (psi). The design is also based on a concrete flexural strength or modulus of rupture of 550 psi. 9.0 Construction Field Reviews Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met. This will require field and engineering review to:  Monitor and test structural fill placement and soil compaction  Observe bearing capacity at foundation locations  Monitor pavement subgrade conditions DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 GEOTECHNICAL INVESTIGATION RENTON, WASHINGTON June 17, 2019 10 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097  Observe slab-on-grade preparation  Observe subsurface drainage systems  Observe excavation stability Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. 10.0 Closure This report was prepared for the exclusive use of VY Properties, LLC and their appointed consultants. Any use of this report or the material contained herei n by third parties, or for other than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC. The recommendations contained in this report are based on assumed continuity of soils with those of our test holes, and assumed structural loads. Cobalt Geosciences should be provided with final architectural and civil drawings when they become available in order that we may review our design recommendations and advise of any revisions, if necessary. Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the responsibility of VY Properties, LLC who is identified as “the Client” within the Statement of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of these not be satisfied. Respectfully submitted, Cobalt Geosciences, LLC Original signed by: DRAFT ONLY – NOT FOR PERMITTING Phil Haberman, PE, LG, LEG Principal PH/sc DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 APPENDIX A Statement of General Conditions DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 Statement of General Conditions USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and may not be used by any third party without the express written consent of Cobalt Geosciences and the Client. Any use which a third party makes of this report is the responsibility of such third party. BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are in accordance with Cobalt Geosciences present understanding of the site specific project as described by the Client. The applicability of these is restricted to the site conditions encountered at the time of the investigation or study. If the proposed site specific project differs or is modified from what is described in this report or if the site conditions are altered, this report is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the report to reflect the differing or modified project specifics and/or the altered site conditions. STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in accordance with the normally accepted standard of care in the state of execution for the specific professional service provided to the Client. No other warranty is made. INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and statements regarding their condition, made in this report are based on site conditions encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or sampling locations. Classifications and statements of condition have been made in accordance with normally accepted practices which are judgmental in nature; no specific description should be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in situ conditions can only be made to some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock and groundwater conditions as influenced by geological processes, construction activity, and site use. VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be encountered that are different from those described in this report or encountered at the test locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected conditions are substantial and if reassessments of the report conclusions or recommendations are required. Cobalt Geosciences will not be responsible to any party for damages incurred as a result of failing to notify Cobalt Geosciences that differing site or sub-surface conditions are present upon becoming aware of such conditions. PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next project stage (property acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated project specifics and that the contents of this report have been properly interpreted. Specialty quality assurance services (field observations and testing) during construction are a necessary part of the evaluation of sub-subsurface conditions and site preparation works. Site work relating to the recommendations included in this report should only be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be responsible for site work carried out without being present. DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 10.2 PO Box 82243 Kenmore, WA 98028 cobaltgeo@gmail.com 206-331-1097 APPENDIX B Figures: Vicinity Map, Site Plan DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 SITE N Project Location Renton WASHINGTON VICINITY MAP FIGURE 1 Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 (206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com Proposed Residential Development 122xx SE Petrovitsky Road Renton, Washington DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 (206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com SITE PLAN FIGURE 2 N Proposed Residential Development 122xx SE Petrovitsky Road Renton, Washington TP-1 TP-4 TP-1 TP-2 TP-3 DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 APPENDIX C Test Pit Logs DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 PT Well-graded gravels, gravels, gravel-sand mixtures, little or no fines Poorly graded gravels, gravel-sand mixtures, little or no fines Silty gravels, gravel-sand-silt mixtures Clayey gravels, gravel-sand-clay mixtures Well-graded sands, gravelly sands, little or no fines COARSE GRAINED SOILS (more than 50% retained on No. 200 sieve) Primarily organic matter, dark in color, and organic odor Peat, humus, swamp soils with high organic content (ASTM D4427)HIGHLY ORGANIC SOILS FINE GRAINED SOILS (50% or more passes the No. 200 sieve) MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION Gravels (more than 50% of coarse fraction retained on No. 4 sieve) Sands (50% or more of coarse fraction passes the No. 4 sieve) Silts and Clays (liquid limit less than 50) Silts and Clays (liquid limit 50 or more) Organic Inorganic Organic Inorganic Sands with Fines (more than 12% fines) Clean Sands (less than 5% fines) Gravels with Fines (more than 12% fines) Clean Gravels (less than 5% fines) Unified Soil Classification System (USCS) Poorly graded sand, gravelly sands, little or no fines Silty sands, sand-silt mixtures Clayey sands, sand-clay mixtures Inorganic silts of low to medium plasticity, sandy silts, gravelly silts, or clayey silts with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays Organic silts and organic silty clays of low plasticity Inorganic silts, micaceous or diatomaceous fine sands or silty soils, elastic silt Inorganic clays of medium to high plasticity, sandy fat clay, or gravelly fat clay Organic clays of medium to high plasticity, organic silts Moisture Content Definitions Grain Size Definitions Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (0.08 mm) Sand -Fine -Medium -Coarse Gravel -Fine -Coarse Cobbles Boulders #200 to #40 (0.08 to 0.4 mm) #40 to #10 (0.4 to 2 mm) #10 to #4 (2 to 5 mm) #4 to 3/4 inch (5 to 19 mm) 3/4 to 3 inches (19 to 76 mm) 3 to 12 inches (75 to 305 mm) >12 inches (305 mm) Classification of Soil Constituents MAJOR constituents compose more than 50 percent, by weight, of the soil. Major constituents are capitalized (i.e., SAND). Minor constituents compose 12 to 50 percent of the soil and precede the major constituents (i.e., silty SAND). Minor constituents preceded by “slightly” compose 5 to 12 percent of the soil (i.e., slightly silty SAND). Trace constituents compose 0 to 5 percent of the soil (i.e., slightly silty SAND, trace gravel). Relative Density Consistency (Coarse Grained Soils) (Fine Grained Soils) N, SPT, Relative Blows/FT Density 0 - 4 Very loose 4 - 10 Loose 10 - 30 Medium dense 30 - 50 Dense Over 50 Very dense N, SPT, Relative Blows/FT Consistency Under 2 Very soft 2 - 4 Soft 4 - 8 Medium stiff 8 - 15 Stiff 15 - 30 Very stiff Over 30 Hard Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 (206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com Soil Classification Chart Figure C1 DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 Proposed Development 122xx SE Petrovitsky Road Renton, Washington Test Pit Logs Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 (206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com Test Pit TP-1 Date: May 30, 2019 Contractor: Jim Depth: 10’ Elevation:Logged By: PH Checked By: SC Groundwater: None Material Description Moisture Content (%)Plastic Limit Liquid Limit 10 20 30 400 50 1 2 3 4 5 6 DCP Equivalent N-Value 7 8 9 10 Loose to medium dense, silty-fine to medium grained sand with gravel, mottled yellowish brown to grayish brown, moist. (Weathered Glacial Till) SM/ ML Dense to very dense, silty-fine to fine grained sand with gravel, grayish brown, moist. (Glacial Till) SM/ ML End of Test Pit 10’ Topsoil/Grass Test Pit TP-2 Date: May 30, 2019 Contractor: Jim Depth: 8’ Elevation:Logged By: PH Checked By: SC Groundwater: None Material Description Moisture Content (%)Plastic Limit Liquid Limit 10 20 30 400 50 1 2 3 4 5 6 DCP Equivalent N-Value 7 8 9 10 Loose to medium dense, silty-fine to medium grained sand with gravel, mottled yellowish brown, moist. (Weathered Glacial Till) SM/ ML Dense to very dense, silty-fine to fine grained sand with gravel, grayish brown, moist. (Glacial Till) SM/ ML End of Test Pit 8’ Topsoil/Grass SM Loose to medium dense, silty-fine to medium grained sand with gravel, dark yellowish brown, moist. (Fill) Loose to medium dense, silty-fine to medium grained sand with gravel, dark yellowish brown, moist. (Fill) SM DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606 Proposed Development 122xx SE Petrovitsky Road Renton, Washington Test Pit Logs Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 (206) 331-1097 www.cobaltgeo.com cobaltgeo@gmail.com Test Pit TP-3 Date: May 30, 2019 Contractor: Jim Depth: 10’ Elevation:Logged By: PH Checked By: SC Groundwater: None Material Description Moisture Content (%)Plastic Limit Liquid Limit 10 20 30 400 50 1 2 3 4 5 6 DCP Equivalent N-Value 7 8 9 10 Loose to medium dense, silty-fine to medium grained sand with gravel, mottled yellowish brown to grayish brown, moist. (Weathered Glacial Till) SM/ ML Dense to very dense, silty-fine to fine grained sand with gravel, grayish brown, moist. (Glacial Till) SM/ ML End of Test Pit 10’ Topsoil/Grass Test Pit TP-4 Date: May 30, 2019 Contractor: Jim Depth: 8’ Elevation:Logged By: PH Checked By: SC Groundwater: None Material Description Moisture Content (%)Plastic Limit Liquid Limit 10 20 30 400 50 1 2 3 4 5 6 DCP Equivalent N-Value 7 8 9 10 Loose to medium dense, silty-fine to medium grained sand with gravel, mottled yellowish brown, moist. (Weathered Glacial Till) SM/ ML Dense to very dense, silty-fine to fine grained sand with gravel, grayish brown, moist. (Glacial Till) SM/ ML End of Test Pit 8’ Topsoil/Grass Loose to medium dense, silty-fine to medium grained sand with gravel, dark yellowish brown, moist. (Fill) SM DocuSign Envelope ID: 6FEDE754-AC7F-4A9A-847E-EDB66D55B606