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HomeMy WebLinkAboutRS_LaFortuna_Geotechnical_Report_190731_v1.pdfSouth Sound Geotechnical Consulting July 31, 2019 Habitat for Humanity – Seattle/King County 560 Naches Avenue SW, Suite 110 Renton, WA 98057 Attention: Mr. Brett VanSlyke Subject: Geotechnical Engineering Report LaFortuna Development 127th Avenue E. Renton, Washington SSGC Project No. 19061 Mr. VanSlyke, South Sound Geotechnical Consulting (SSGC) has completed a geotechnical assessment for the above referenced project. Our services have been completed in general conformance with our proposal P19056 (dated June 13, 2019) and authorized per signature of our services agreement. Our evaluation included completion of four test pits on the property, engineering analyses, and preparation of this report. PROJECT INFORMATION Three town-house buildings are planned on the property, located near the looped portion of 127th Street SE, south of SE 172nd Street. Conventional spread footing foundations will be used for support of the structures, with concrete slab-on-grade floors. SITE CONDITIONS The property is characterized with west-facing sloping ground in the eastern portion, with relatively level ground in the western portion. Overall elevation change across the site is on the order of 24 (+/-) feet. The upper eastern site is covered with grass. The western portions are used for equipment storage and construction offices. It appears that cuts on the east side of 127th Street SE were completed for the road and have resulted in steeper cut slopes in this area. SUBSURFACE CONDITIONS Subsurface conditions were characterized by completing four test pits on the site on July 9, 2019. Test pits were advanced to final depths between about 3.5 and 5 feet below existing ground surface. Approximate locations of the test pits are shown on Figure 1, Exploration Plan. Logs of the test pits are provided in Appendix A. A summary description of observed subgrade conditions is provided below. RECEIVED 11/04/2019 amorganroth PLANNING DIVISION Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 2 Soil Conditions Fill was observed below the surface in two of the test pits (TP-1 and TP-2). Fill at the TP-1 location was crushed gravel for a working surface and on the order of 6 inches thick. Fill at the TP-2 location consisted of mixed silt, sand, and gravel in a loose condition. This fill extended to about 3 feet. An approximate 6 inch topsoil layer was at the surface of the remaining test pits. Native soil below the fill (or topsoil) was silty sand with gravel and occasional cobbles. It was generally in a medium dense condition below the surface soils and graded dense at shallow depth. This soil is interpreted to be glacial till and continued to the termination depth of the test pits. Groundwater Conditions Groundwater was not observed in the test pits at the time of excavation. Dense glacial till is considered impermeable to vertical groundwater flow and can cause perched groundwater conditions, particularly during the wetter seasons of the year. Wetlands are west of the site on lower elevated ground. Groundwater levels should be anticipated to fluctuate due to seasonal precipitation variations and on- and off-site drainage patterns. Geologic Setting Soils within the project area have been classified by the NRCS Soil Survey. Site soils are mapped as Alderwood gravelly sandy loam. Alderwood soils reportedly formed in glacia l till. Native soils in the excavations appear to conform to the mapped soil type. GEOTECHNICAL DESIGN CONSIDERATIONS Planned development of this site is considered feasible based on observed soil conditions in the test pits. Properly prepared native soils can be used for support of conventional spread footing foundations and pavements. Daylight basement structures are anticipated for buildings on the east side of 127 th Avenue SE where grades rise to the east from street elevation. Infiltration to assist in stormwater control is not considered feasible at this site. The dense glacial till at shallow depth will create a barrier to vertical groundwater flow. Recommendations presented in the following sections should be considered general and may require modifications when earthwork and grading occur. They are based upon the subsurface conditions observed in the test pits and the assumption that finish site grades will be similar to existing grades. It should be noted subsurface conditions across the site may vary from those depicted on the exploration logs and can change with time, especially on sites with previous development. Therefore, proper site preparation will depend upon the weather and soil conditions encountered at the time of construction. We recommend SSGC review final plans and further assess subgrade conditions at the time of construction, as warranted. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 3 General Site Preparation Site grading and earthwork should include procedures to control surface water runoff. Grading the site without adequate drainage control measures may negatively impact site soils, resulting in increased export of impacted soil and import of fill materials, potentially increasing the cost of the earthwork and subgrade preparation phases of the project. Site grading should include removal (stripping) of topsoil and fill or very loose or soft soils encountered in building and pavement areas. Subgrades should consist of firm, undisturbed native till following stripping. Stripping depths in the area of test pit TP-2 may approach 4 feet (or more), but can only be determined at the time of construction. Shallower stripping depths are expected over most of the remaining site. General Subgrade Preparation Subgrades in building footprints and pavement areas should consist of firm, undisturbed native soil. We recommend exposed subgrades in building and conventional pavement areas are proofrolled using a large roller, loaded dump truck, or other mechanical equipment to assess subgrade conditions following stripping. Proofrolling efforts should result in the upper 1 foot of subgrade soils in building and conventional pavement areas achieving a compaction level of at least 95 percent of the maximum dry density (MDD) per the ASTM D1557 test method. Wet, loose, or soft subgrades that cannot achieve this compaction level should be removed (over-excavated) and replaced with structural fill. The depth of over-excavation should be based on soil conditions at the time of construction. A representative of SSGC should be present to assess subgrade conditions during proofrolling. Grading and Drainage Positive drainage should be provided during construction and maintained throughout the life of the development. Allowing surface water into cut or fill areas, utility trenches and building footprints should be prevented. Temporary and permanent drainage systems should prevent stormwater from flowing onto the steeper south-facing slope. Structural Fill Materials The suitability of soil for use as structural fill will depend on the gradation and moisture content of the soil when it is placed. Soils with higher fines content (soil fraction passing the U.S. No. 200 sieve) will become sensitive with higher moisture content. It is often difficult to achieve adequate compaction if soil moisture is outside of optimum ranges for soils that contain more than about 5 percent fines. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 4 Site Soils: Topsoil and observed fill are not considered suitable as structural fill. They could be used in non-structural areas, such as lawns. Native glacial till could be suitable for use as structural fill provided it can be moisture conditioned to within optimal ranges. Till can have considerable fine (silt) content and therefore will be moisture sensitive and difficult to use as structural fill if wet. Optimum moisture is considered within about +/- 2 percent of the moisture content required to achieve the maximum dry density (MDD) per the ASTM D-1557 test method. If moisture content is higher or lower than optimum, soils would need to be dried or wetted prior to placement as structural fill. Import Fill Materials: We recommend import structural fill placed during dry weather consist of material which meets the specifications for Gravel Borrow as described in Section 9-03.14(1) of the 2018 Washington State Department of Transportation (WSDOT) Specifications for Road, Bridge, and Municipal Construction (Publication M 41-10). Gravel Borrow should be protected from disturbance if exposed to wet conditions after placement. During wet weather, or for backfill on wet subgrades, import soil suitable for compaction in wetter conditions should be provided. Imported fill for use in wet conditions should conform to specifications for Select Borrow as described in Section 9-03.14(2), or Crushed Surfacing per Section 9-03.9(3) of the 2018 WSDOT M-41 manual, with the modification that a maximum of 5 percent by weight shall pass the U.S. No. 200 sieve for these soil types. Structural fill placement and compaction is weather-dependent. Delays due to inclement weather are common, even when using select granular fill. We recommend site grading and earthwork be scheduled for the drier months of the year. Structural fill should not consist of frozen material. Structural Fill Placement We recommend structural fill is placed in lifts not exceeding about 10 inches in loose measure. It may be necessary to adjust lift thickness based on site and fill conditions during placement and compaction. Finer grained soil used as structural fill and/or lighter weight compaction equipment may require significantly thinner lifts to attain required compaction levels. Granular soil with lower fines contents could potentially be placed in thicker lifts if they can be adequately compacted. Structural fill should be compacted to attain the recommended levels presented in Table 1, Compaction Criteria. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 5 Table 1. Compaction Criteria Fill Application Compaction Criteria* Footing areas 95 % Upper 2 feet in pavement areas, slabs and sidewalks, and utility trenches 95 % Below 2 feet in pavement areas, slabs and sidewalks, and utility trenches 92 % Utility trenches or general fill outside of paved or building areas 90 % *Per the ASTM D 1557 test method. Trench backfill within about 2 feet of utility lines should not be over-compacted to reduce the risk of damage to the line. In some instances the top of the utility line may be within 2 feet of the surface. Backfill in these circumstances should be compacted to a firm and unyielding condition. We recommend fill procedures include maintaining grades that promote drainage and do not allow ponding of water within the fill area. The contractor should protect compacted fill subgrades from disturbance during wet weather. In the event of rain during structural fill placement, the exposed fill surface should be allowed to dry prior to placement of additional fill. Alternatively, the we t soil can be removed. We recommend consideration is given to protecting haul routes and other high traffic areas with free-draining granular fill material (i.e. sand and gravel containing less than 5 percent fines) or quarry spalls to reduce the potential for disturbance to the subgrade during inclement weather. Structural or embankment fill placed on slopes should be benched into firm (dense) native glacial till. Benches should be excavated level (or with a slight incline into the hillside). Benches should be a maximum of 2 feet high and wide enough to accommodate a conventional vibratory smooth-drum roller capable of compacting fill to at least 95 percent of the MDD per the ASTM D 1557 test method. Earthwork Procedures Conventional earthmoving equipment should be suitable for earthwork at this site. Earthwork may be difficult during periods of wet weather or if elevated soil moisture is present. Excavated site soils may not be suitable as structural fill depending on the soil moisture content and weather conditions at the time of earthwork. If soils are stockpiled and wet weather is anticipated, the stockpile should be protected with securely anchored plastic sheeting. If stockpiled soils become wet and unusable, it will become necessary to import clean, granular soils to complete wet weather site work. Wet or disturbed subgrade soils should be over-excavated to expose firm, non-yielding, non-organic soils and backfilled with compacted structural fill. We recommend the earthwork portion of this project be completed during extended periods of dry weather. If earthwork is completed during the wet season (typically October through May) it may be necessary to take extra measures to protect subgrade soils. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 6 If earthwork takes place during freezing conditions, we recommend the exposed subgrade is allowed to thaw and re-compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen soil can be removed to unfrozen soil and replaced with structural fill. The contractor is responsible for designing and constructing stable, temporary excavations (including utility trenches) as required to maintain stability of excavation sides and bottoms. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards. Temporary excavation cuts should be sloped at inclinations of 1H:1V (Horizontal:Vertical) or flatter, unless the contractor can demonstrate the safety of steeper cut slopes. Permanent cut and fill slopes should be inclined at 2H:1V, or flatter. Erosion control measures should be implemented on all temporary and permanent cut or fill slopes immediately after grading. A qualified geotechnical engineer and materials testing firm should be retained during the construction phase of the project to observe earthwork operations and to perform necessary tests and observations during subgrade preparation, placement and compaction of structural fill, and backfilling of excavations. Foundations Foundations can be placed on native glacial till or on a zone of structural fill above prepared native subgrades as described in this report. The following recommendations are for conventional spread footing foundations: Bearing Capacity (net allowable): 3,000 pounds per square foot (psf) for footings supported on firm native till subgrades or structural fill prepared as described in this report. Footing Width (Minimum): 16 inches (Strip) 24 inches (Column) Embedment Depth (Minimum): 18 inches (Exterior) 12 inches (Interior) Settlement: Total: < 1 inch Differential: < 1/2 inch (over 30 feet) Allowable Lateral Passive Resistance: 325 psf/ft* (below 12 inches) Allowable Coefficient of Friction: 0.40* *These values include a factor of safety of approximately 1.5. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 7 The net allowable bearing pressures presented above may be increased by one -third to resist transient, dynamic loads such as wind or seismic forces. Lateral resistance to footings should be ignored in the upper 12-inches from exterior finish grade. Foundation Construction Considerations All foundation subgrades should be free of water and loose soil prior to placing concrete , and should be prepared as recommended in this report. Concrete should be placed soon after excavating and compaction to reduce disturbance to bearing soils. Should soils at foundation level become excessively dry, disturbed, saturated, or frozen, the affected soil should be removed prior to placing concrete. We recommend SSGC observe all foundation subgrades prior to placement of concrete. Foundation Drainage Ground surface adjacent foundations should be sloped away to facilitate drainage. We recommend footing drains are installed around perimeter footings. Footing drains should include a minimum 4- inch diameter perforated rigid plastic or metal drain line installed along the exterior base of the footing. The perforated drain lines should be connected to a tight line pipe that discharges to an approved storm drain receptor. The drain line should be surrounded by a zone of clean, free-draining granular material having less than 5 percent passing the No. 200 sieve or meeting the requirements of section 9-03.12(2) “Gravel Backfill for Walls” in the 2018 WSDOT (M41-10) manual. The free- draining aggregate zone should be at least 12 inches wide and wrapped in filter fabric. The granular fill should extend to within 6 inches of final grade where it should be capped with compacted fill containing sufficient fines to reduce infiltration of surface water into the footing drains. Alternately, the ground surface can be paved with asphalt or concrete. Cleanouts are recommended for maintenance of the drain system. On-Grade Floor Slabs On-grade floor slabs should be placed on native soils or structural fill prepared as described in this report. We recommend a modulus subgrade reaction of 200 pounds per square inch per inch (psi/in) for upper native soil or compacted granular structural fill over properly prepared native soil. An increased subgrade reaction of 250 (psi/in) can be used for slabs placed on dense glacial till. We recommend a capillary break is provided between the prepared subgrade and bottom of slab. Capillary break material should be a minimum of 4 inches thick and consist of compacted clean, free- draining, well graded course sand and gravel. The capillary break material should contain less than 5 percent fines, based on that soil fraction passing the U.S. No. 4 sieve. Alternatively, a clean angular gravel such as No. 7 aggregate per Section 9-03.1(4) C of the 2018 WSDOT (M41-10) manual could be used for this purpose. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 8 We recommend positive separations and/or isolation joints are provided between slabs and foundations, and columns or utility lines to allow independent movement where needed. Backfill in interior trenches beneath slabs should be compacted in accordance with recommendations presented in this report. A vapor retarder should be considered beneath concrete slabs that will be covered with moisture sensitive or impervious coverings (such as tile, wood, etc.), or when the slab will support equipment or stored materials sensitive to moisture. We recommend the slab designer refer to ACI 302 and/or ACI 360 for procedures and limitations regarding the use and placement of vapor retarders. Lateral Earth Pressures Below grade and retaining walls will be subject to lateral earth pressures. Subgrade walls are typi cally designed for “active” or “at-rest” earth pressure conditions. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes lateral movement at the top of the wall of around 0.002H to 0.004H, where H is the height of the wall. The at-rest condition assumes no wall movement. The following recommended earth pressures (Table 2) should be applied as a triangular distribution starting at the top of the wall (for active and at-rest) and bottom of wall (for passive) and assume:  Backfill behind walls is level and no surcharge loads will be applied;  Drainage is provided behind the wall to prevent the development of hydrostatic pressures. Table 2. Lateral Earth Pressures Soil Type Earth Pressure Coefficient* Equivalent Fluid Pressure (pcf)* Native Glacial Till Active: 0.28 At-rest: 0.44 Passive: 3.50 Active: 30 At-rest: 45 Passive: 350 * A factor of safety of about 1.5 should be applied to these values. Additional lateral pressure should be added to these values to model surcharges such as sloped backfill, traffic, construction, or seismic loads. We recommend an active seismic pressure of 4H psf (where H is the height of the subgrade wall) and an at-rest seismic pressure of 7H. The effects of other surcharge loads should be accounted for as appropriate. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 9 Wall Backfill Backfill behind the drainage zone should consist of granular material that satisfies the criteria of Section 9-03.12(2) “Gravel Backfill for Walls” per the 2018 WSDOT (M 41-10) manual, or as approved by the engineer. Backfill should be placed in lifts not exceeding 8 inches and compacted with hand-operated compaction equipment. Compaction of wall backfill should be between 90 to 92 percent of the maximum dry density (MDD) per the ASTM D1557 test method within 3 feet of the back of the wall to limit additional lateral pressures. At a distance greater than 3 feet behind the back of the wall, backfill can be compacted using conventional rollers, with backfill compacted to at least 92 percent of the MDD. Seismic Considerations Seismic parameters and values in Table 3 are based on the 2015 International Building Code (IBC). Table 3. Seismic Parameters PARAMETER VALUE 2015 International Building Code (IBC) Site Classification1 C Ss Spectral Acceleration for a Short Period 1.381 S1 Spectral Acceleration for a 1-Second Period 0.515g Fa Site Coefficient for a Short Period 1.00 Fv Site Coefficient for a 1-Second Period 1.3 1 Note: In general accordance with 2015 International Building Code, Section 1613.3.1 for risk categories I,II,III. IBC Site Class is based on estimated characteristics of the upper 100 feet of the subsurface profile. Ss, S1, Fa, and Fv values based on the OSHPD Seismic Design Maps website. Liquefaction Soil liquefaction is a condition where loose, typically granular soils located below the groundwater surface lose strength during ground shaking, and is often associated with earthquakes. The King County “Liquefaction Susceptibility” map (Map 11-5) shows the property in an area with low susceptibility to liquefaction. Native soils at fairly shallow depth consists of dense to very dense glacial till. The risk of liquefaction at this site is considered low for the design level earthquake. Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 10 Infiltration Characteristics Infiltration to control stormwater is not considered feasible at this site due to the presence of dense glacial till at shallow depths. Assessment of infiltration rates using small-scale Pilot Infiltration Test (PIT) procedures in similar soils in the area have shown negligible infiltration during the soak period of the test. Other detention/retention facilities will be required to control stormwater runoff at this site. Critical Areas Site slopes with heights of 10 feet or more have average inclinations between about 15 to 20 percent based on topographic information on the “Boundary and Topographic Survey” of the site completed by 4Site Surveying and Consulting, dated April 3, 2019. The site is not identified on the City of Renton GIS Landslide Hazard Severity map. Test pits on the site and geologic/soil maps indicate underlying native soils that comprise site slopes consist of glacial till. Slopes comprised of dense glacial till with inclinations of less than 20 percent are generally considered stable and not subject to significant movement. Evidence of recent or historic landslides was not observed on site slopes. We are unaware of any known deeper seated landslides within 300 feet of the site. The proposed development will not adversely impact site or neighboring slopes, in our opinion. REPORT CONDITIONS This report has been prepared for the exclusive use of Habitat for Humanity for specific application to the project discussed, and has been prepared in accordance with generally accepted geotechnical engineering practices in the area. No warranties, either express or i mplied, are intended or made. The analysis and recommendations presented in this report are based on observed soil conditions and test results at the indicated locations, and from other geologic information discussed. This report does not reflect variations that may occur across the site, or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplementa l recommendations can be provided. This report was prepared for the planned type of development of the site as discussed herein. It is not valid for third party entities or alternate types of development on the site without the express written consent of SSGC. If development plans change we should be notified to review those changes and modify our recommendations as necessary. N South Sound Geotechnical Consulting P.O. Box 39500 Lakewood, WA 98496 (253) 973-0515 Figure 1 – Exploration Plan LaFortuna Renton, WA SSGC Project #19061 Approximate Test Pit Location PIT - 1 TP - 1 TP-1 TP-1 Scale: NTS Base map from “Boundary and Topographic Survey of 12710 – 173rd Pl”, by 4Site Surveying and Consulting, dated 4-3-19. Legend TP-2 TP-1 TP-3 TP-1 TP-4 TP-1 Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 A-1 Appendix A Field Exploration Procedures and Test Pit Logs Geotechnical Engineering Report SSGC LaFortuna Development 127th Avenue SE Renton, Washington SSGC Project No. 19061 July 31, 2019 Field Exploration Procedures Our field exploration for this project included four test pits completed on July 9, 2019. The approximate locations of the explorations are shown on Figure 1, Exploration Plan. The exploration locations were determined by pacing from site features. Ground surface elevations referenced on the logs were inferred from Google Earth satellite imagery. Exploration locations and elevations should be considered accurate only to the degree implied by the means and methods used. A client provided excavator dug the test pits. Soil samples were collected and stored in moisture tight containers for further assessment and laboratory testing. Explorations were backfilled with excavated soils and tamped when completed. Please note that backfill in the explorations will likely settle with time. Backfill material located in building areas should be re-excavated and recompacted, or replaced with structural fill. The following logs indicate the observed lithology of soils and other materials observed in the explorations at the time of excavation. Where a soil contact was observed to be gradational, our log indicates the average contact depth. Our logs also indicate the approximate depth to groundwater (where observed at the time of excavation), along with sample numbers and approximate sample depths. Soil descriptions on the logs are based on the Unified Soil Classification System. Project: LaFortuna SSGC Job # 19061 TEST PIT LOGS PAGE 1 OF 2 Location: Renton, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 TO TP-4 Logged by: THR Test Pit TP-1 Depth (feet) Material Description 0 – 0.5 0.5 – 4 Fill: Crushed Gravel Silty SAND with gravel and occasional cobble: Medium dense to dense, moist, brownish gray. (Glacial Till) Test pit completed at approximately 4 feet on 7/9/19. Groundwater not observed at time of excavation. Approximate surface elevation: 388 feet Test Pit TP-2 Depth (feet) Material Description 0 – 3 3 – 5 Fill: Silt, sand, gravel: Loose, damp, brown. Silty SAND with gravel and occasional cobble: Medium dense to dense, moist, brownish gray. (Glacial Till) Test pit completed at approximately 5 feet on 7/9/19. Groundwater not observed at time of excavation. Approximate surface elevation: 400 feet Test Pit TP-3 Depth (feet) Material Description 0 – 0.5 0.5 – 3.5 Topsoil Silty SAND with gravel and occasional cobble: Medium dense to dense, moist, light brown. (Glacial Till) Test pit completed at approximately 3.5 feet on 7/9/19. Groundwater not observed at time of excavation. Approximate surface elevation: 403 feet UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification Group Symbol Group NameB Coarse Grained Soils More than 50% retained on No. 200 sieve Gravels More than 50% of coarse fraction retained on No. 4 sieve Clean Gravels Less than 5% finesC Cu  4 and 1  Cc  3E GW Well-graded gravelF Cu  4 and/or 1  Cc  3E GP Poorly graded gravelF Gravels with Fines More than 12% finesC Fines classify as ML or MH GM Silty gravelF,G, H Fines classify as CL or CH GC Clayey gravelF,G,H Sands 50% or more of coarse fraction passes No. 4 sieve Clean Sands Less than 5% finesD Cu  6 and 1  Cc  3E SW Well-graded sandI Cu  6 and/or 1  Cc  3E SP Poorly graded sandI Sands with Fines More than 12% finesD Fines classify as ML or MH SM Silty sandG,H,I Fines Classify as CL or CH SC Clayey sandG,H,I Fine-Grained Soils 50% or more passes the No. 200 sieve Silts and Clays Liquid limit less than 50 inorganic PI  7 and plots on or above “A” lineJ CL Lean clayK,L,M PI  4 or plots below “A” lineJ ML SiltK,L,M organic Liquid limit - oven dried  0.75 OL Organic clayK,L,M,N Liquid limit - not dried Organic siltK,L,M,O Silts and Clays Liquid limit 50 or more inorganic PI plots on or above “A” line CH Fat clayK,L,M PI plots below “A” line MH Elastic SiltK,L,M organic Liquid limit - oven dried  0.75 OH Organic clayK,L,M,P Liquid limit - not dried Organic siltK,L,M,Q Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-in. (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW -GM well-graded gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded sand with silt, SW -SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D60/D10 Cc = 6010 2 30 DxD )(D F If soil contains  15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. HIf fines are organic, add “with organic fines” to group name. I If soil contains  15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. L If soil contains  30% plus No. 200 predominantly sand, add “sandy” to group name. M If soil contains  30% plus No. 200, predominantly gravel, add “gravelly” to group name. N PI  4 and plots on or above “A” line. O PI  4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line. Project: LaFortuna SSGC Job # 19061 TEST PIT LOGS PAGE 2 OF 2 Location: Renton, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 TO TP-4 Logged by: THR Test Pit TP-4 Depth (feet) Material Description 0 – 0.5 0.5 – 4 Topsoil Silty SAND with gravel and occasional cobble: Medium dense to dense, moist, light brown. (Glacial Till) Test pit completed at approximately 4 feet on 7/9/19. Groundwater not observed at time of excavation. Approximate surface elevation: 410 feet