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HomeMy WebLinkAboutRS_GeotechReport_250123_v1________________________________________________ 3213 Eastlake Avenue East, Suite B Seattle, WA 98102 (206) 262-0370 | pangeoinc.com Geotechnical & Earthquake Engineering Consultants January 13, 2025 Project No. 24-497 Tony Halsey, P.E. Kite Realty Group 30 South Meridian Street, Suite 1100 Indianapolis, IN 46204 Subject: Limited Geotechnical Report Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA 98055 Dear Tony: As requested, PanGEO, Inc. completed a geotechnical study to support the design and permitting of the proposed retaining wall at the above-referenced site in Renton, Washington. Our service scope included reviewing readily available geologic and geotechnical data in the vicinity of the project, conducting a reconnaissance of the site, performing limited subsurface investigations, and formulating the conclusions and recommendations presented in this report. Our work was completed in accordance with our proposal for geotechnical engineering services, dated December 20, 2024, and the professional services agreement with you, dated 1/3/2025. SITE & PROJECT DESCRIPTION The subject site is located at 17803 108th Avenue SE, in Renton, Washington, as shown on the attached Figure 1, Vicinity Map. The site is bounded by 108th Avenue SE/Benson Road South to the east, and by commercial properties to the north, west and south, anchored by the Fred Meyer retail store to the west. The project site is currently developed with a one-level at-grade structure that was formerly a Bank of America branch. The structure is surrounded with asphalt parking areas and driveways. The majority of the site is relatively flat, with the exception of the eastern margin of the site that slopes up from the parking lot at an angle of about 2H:1V to the sidewalk of 108th Avenue SE, with a vertical relief of about 12 feet. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 2 PanGEO, Inc. The specific focus of our current study is the slope on the eastern portion of the site. As part of the proposed re-development of the property, we understand that the City of Renton is requiring street improvements along the frontage of the subject property, which includes the addition of a planter strip and widened sidewalk which will extend over the existing slope on the east side of the subject site. As such, a new retaining wall will need to be incorporated into the project to support the new sidewalk, and/or retain the fill soils placed to support the new sidewalk. Plates 1 and 2 below depict current site conditions. Plate 1. Looking north-northeast at the slope on the east side of the property where the proposed retaining wall will be constructed. A portion of the existing bank drive-through structure can be seen on the left side of the photo. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 3 PanGEO, Inc. Plate 2. Looking south along the western sidewalk of 108th Avenue SE. The proposed retaining wall will be located near the toe of the slope shown on the right side of the photo. The conclusions and recommendations outlined in this report are based on our understanding of the proposed project, which is in turn based on the project information provided to us. If the above project description is substantially different from the proposed improvements, or if the project scope changes, PanGEO should be consulted to review the recommendations contained in this study and make modifications, if needed. SUBSURFACE EXPLORATIONS Our subsurface exploration program included advancing four (4) hand borings (PG-1 to PG-4) on December 30, 2024, to explore near-surface soil conditions at the location of the proposed retaining wall and backslope. The boring locations are shown on Figure 2, Site and Exploration Plan, and were measured in the field from existing site features. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 4 PanGEO, Inc. The hand borings were advanced utilizing a post-hole digger and a 4-inch diameter hand auger to depths of up to 4½-feet below the existing ground surface. An engineer from PanGEO performed the explorations and logged the subsurface conditions encountered in the test holes. The relative density of granular soils and the relative consistency of cohesive soils were generally estimated based on the excavation resistance encountered throughout the depth of the exploration, and on the penetration resistance of the soil from a ½-inch diameter steel hand probe. After each test hole was completed, it was backfilled with excavated spoils, and the surface tamped firm. The summary hand boring logs are included in Appendix A at the end of this report. The soil samples were described using the system outlined in Appendix A, Figure A-1. GEOLOGY General geologic information for the project area was obtained by reviewing the Geologic Map of the Renton Quadrangle, King County, Washington (Mullineaux, 1965) and the Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington (Schuster et al, 2015). Based on our review, the geologic unit in the vicinity of the site consists of Vashon till – Geologic Map Unit Qgt. Vashon till is described as consisting of an unsorted deposit (diamict) of clay, silt, sand and gravel that has been glacially transported and deposited. This soil has been directly deposited by a glacier and overridden by several thousand feet of glacial ice and is typically dense to very dense. Plate 3 on the following page depicts and excerpt from the geologic map by Schuster et at, 2015. SUBSURFACE CONDITIONS SOIL CONDITIONS Based on the conditions encountered in our test borings, the area of the proposed retaining wall is generally underlain by a relatively thin layer of undocumented fill over medium dense to dense silty and with some gravel, which we interpreted to be the mapped glacial till. A summary of the soil units encountered in the explorations is provided below, and details of the soil conditions encountered in each of the test borings can be found in Appendix A. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 5 PanGEO, Inc. Topsoil: All of the test borings encountered from about 6 to 8 inches of loose, dark brown, silty sand and sandy silt with prevalent organics which we interpreted to be topsoil. Fill: Below the organic-rich topsoil, all of the test borings encountered a relatively thin layer of fill, except boring PG-2, where no fill was encountered. The fill typically consisted of loose to medium dense, silty sand and sandy silt with trace to some gravel and scattered organic matter. In general, near the toe of the slope, the fill extended to about 2½ feet below the ground surface, while near the middle of the slope, at the location of PG-3, about two feet of fill was encountered. Plate 3 – Geology map of the area. The site is located in an area mapped as glacial till (map unit Qgt). (Schuster et al, 2015) SITE Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 6 PanGEO, Inc. Drainage Gravel - At the toe of the slope, PG-1 encountered washed drainage rock at a depth from about 1 to 2½ feet below the ground surface. We infer that a drain line may have been installed at the toe of the slope to intercept groundwater seeping from the slope cut to transport the water to a suitable drainage outlet. Glacial Till: Below the topsoil in PG-2, and below the fill in all other borings, we generally encountered a medium dense to dense, silty sand with some gravel that we interpreted to be the mapped glacial till. Due to the medium dense to dense nature of this deposit, and evidence of iron-oxide staining, we inferred that the top of the glacial till deposit encountered in the test borings was weathered, and that the underlying un-weathered soils would become dense to very dense, which his typical of glacial till deposits. Our subsurface descriptions are based on the conditions encountered at the time of our exploration. Soil conditions between our exploration locations may vary from those encountered. The nature and extent of variations between our exploratory locations may not become evident until construction. If variations do appear, PanGEO should be requested to reevaluate the recommendations in this report and to modify or verify them in writing prior to proceeding with earthwork and construction. GROUNDWATER CONDITIONS At the toe of the slope, the test borings encountered groundwater seepage as shallow as 1-foot below the ground surface (see Hand Boring Log – PG-3). All borings encountered soils with iron- oxide stains, which is an indication of groundwater fluctuations within the soil layer. We interpret that the groundwater seepage encountered in PG-3, and the cause of the iron oxide staining in the other borings, is perched water that forms on top of the underlying dense glacial till during wet times of the year. We anticipate that stormwater infiltrates into the ground above the slope, becomes perched on the low permeability till, and then flows downslope to the west, following the contact of the glacial till. We anticipate that a significant amount of groundwater was accumulating at the toe of the slope during original grading of the property, which is the likely reason a drainage measure was installed at the toe of the slope to intercept and collect the groundwater seepage. It may be noted that glacial till deposits also typically contain pockets of clean sand and gravel that can also contain groundwater, which may contribute to seepage once they are excavated into. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 7 PanGEO, Inc. Groundwater levels will change depending on the season, amount of rainfall, surface water runoff, and other factors. Generally, the water level is higher and seepage rates are greater in the wetter, winter months (typically October through May). GEOTECHNICAL RECOMMENDATIONS RETAINING WALL DESIGN Due to the depth of competent bearing soils near the mid-height of the slope (about 4½ feet), in our opinion it will be more cost effective to locate the proposed retaining wall along the toe of the slope, instead of mid-height. Based on the results of our subsurface exploration program and our site reconnaissance, in our opinion a cast-in-place concrete wall located at the toe of the existing slope represents a feasible wall type at the subject site. To limit the wall height, in our opinion, a backslope no steeper than 2H:1V may be constructed behind the wall to support the new frontage improvements. We recommend that the wall be designed to stick up a minimum of 1-foot above the ground surface to account for any erosion that could occur on the backslope behind the wall. Retaining walls should be properly designed to resist the pressure exerted by the soils behind the wall, including a backslope. Proper drainage provisions should also be provided behind the walls to intercept and remove any groundwater from behind the wall. In this particular case, as described above, groundwater seepage is anticipated behind the proposed wall, and therefore adequate drainage provisions are critical, and should not be omitted during the design or construction of the wall. Our geotechnical recommendations for the design and construction of the proposed retaining wall are presented below. Footing Depth and Allowable Bearing Pressure We recommend that the wall footing bears on the undisturbed, medium dense to dense native soils which we estimate is present about 2½ feet below the toe of the slope. As such, the footing will need to be embedded about 2½ feet below the existing pavement elevation, or the soils below the footing should be over-excavated to about 2½ feet below the pavement elevation, and backfilled with properly compacted structural fill or lean-mix concrete (1.5 sack mix, minimum) up to the design footing elevation. We recommend a minimum foundation embedment of 18 inches below final exterior grade. The footings may be designed for a maximum allowable bearing pressure of Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 8 PanGEO, Inc. 3,000 psf. For allowable stress design, the recommended allowable bearing pressure may be increased by 1/3 for transient conditions such as wind and seismic loadings. Lateral Earth Pressures Considering the maximum backslope of 2H:1V, the wall should be designed for an earth pressure based upon an equivalent fluid weight of 53 pcf for a wall that is allowed to yield (active condition), and 35 pcf for a wall with a level backslope. For the seismic condition and a 2H:1V wall backslope, we recommend a uniform lateral earth pressure of 15H psf (where H is the height of the below grade portion of the wall) be added to the static pressure for sizing the walls for the ultimate condition. If the wall backfill will be level, we recommend a uniform lateral earth pressure of 10H psf be added for the seismic condition. The recommended lateral pressures assume that adequate wall drainage will be incorporated into the design and construction of the walls to prevent the development of hydrostatic pressure. Lateral Resistance Lateral forces may be resisted by the combination of passive earth pressures acting against the embedded portions of the foundations and by friction acting on the base of the foundations. Passive resistance values may be determined using an equivalent fluid weight of 300 pounds per cubic foot (pcf), which assumes level ground conditions in front of the wall. This value includes a geotechnical factor of safety of at least 1.5 assuming that properly compacted structural fill will be placed adjacent to the sides of the footings. A coefficient of friction of 0.45 may be used to determine the frictional resistance at the base of the footings. This coefficient includes a geotechnical factor of safety of approximately 1.5. Wall Drainage Provisions for permanent control of subsurface water should be incorporated into the design and construction of the new walls, as groundwater seepage is expected behind the proposed wall. For walls constructed with conventional free-draining backfill, a footing drain consisting of a 4-inch diameter perforated pipe embedded in at least 12 inches of washed gravel wrapped with a geotextile fabric should be placed at the base of the new wall footing. We recommend a minimum 12-inch-wide chimney of free draining gravel be placed behind the wall. In addition, prefabricated drainage mats, such as Mirafi 6000 or equivalent, may be installed behind the walls to promote Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 9 PanGEO, Inc. wall drainage. The drain can likely be connected to the same outlet as an existing drain we anticipate is located along the toe of the slope. Wall Backfill Wall backfill should consist of free draining granular soils. Imported wall backfill may consist of granular soils such as Gravel Borrow (Section 9.03.14 (1) of the 2024 WSDOT Standard Specifications) or approved equivalent. Wall backfill should be moisture conditioned to within about 3 percent of optimum moisture content, placed in loose, horizontal lifts less than 8 inches in thickness, and systematically compacted to a dense and relatively unyielding condition and to at least 95 percent of the maximum dry density, as determined using test method ASTM D 1557 (Modified Proctor). Within 5 feet of the wall, the backfill should be compacted to 90 percent of the maximum dry density. Wall Foundation Performance Total and differential settlements are anticipated to be within tolerable limits for footings designed and constructed as discussed above. Footing settlement under static loading conditions is estimated to be less than approximately 3/4 inch, and differential settlement along the wall should be less than about ½-inch. Global Stability Provided that the proposed retaining wall is founded on spread footings bearing below the fill soils on medium dense to very dense native soils at the toe of the slope, and the recommendations provided in this report are adhered to in the design and construction of the walls, the retaining walls will meet current code requirements for global stability. PERMANENT SLOPES Provided that the proposed retaining wall is backfilled with free-draining imported gravel borrow (Section 9.03.14 (1) of the 2024 WSDOT Standard Specifications) or approved equivalent, and the fill is adequately compacted as described above for wall backfill, we recommend permanent fill slopes be constructed no steeper than 2H:1V (Horizontal:Vertical). All existing topsoil should be removed from the slope before backfilling, and any existing loose/soft fill soils should be re- Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 10 PanGEO, Inc. compacted to a firm condition, or removed, prior to placement on compaction of the granular wall backfill. RETAINING WALL CONSTRUCTION CONSIDERATIONS We offer the following geotechnical considerations related to construction aspects of the proposed cast-in-place retaining wall. Footing Construction Considerations All footing subgrades should be carefully prepared. Any loose soil should be removed from the footing excavations or re-compacted. Footing subgrades should be observed by PanGEO to confirm that the exposed footing subgrade is consistent with the expected conditions and adequate to support the design bearing pressure. As noted above, at the toe of the slope drainage gravel may be encountered during the excavation for the retaining wall footing. We recommend that the drainage gravel be removed below the proposed footing to expose the medium dense to very dense native soils. Footing Subgrade Protection The contractor should be aware that the site soils are sensitive to moisture, and may become disturbed and soft when exposed to inclement weather conditions. If the footing subgrades are exposed to water, it may be necessary to place 3 to 4 inches of clean crushed rock on the prepared footing subgrade, or lean-mix concrete (1.5 sack, minimum), to protect it against moisture and disturbance. Temporary Excavations In general, maximum temporary excavation cuts are expected to be about 12 feet tall. Temporary excavations greater than 4 feet deep should be properly sloped or shored. All temporary excavations should be performed in accordance with Part N of WAC (Washington Administrative Code) 296-155. The contractor is responsible for maintaining safe excavation slopes and/or shoring. For planning purposes, the temporary excavations may be sloped to as steep as 1H:1V (Horizontal:Vertical). The temporary cut slopes should be re-evaluated by a representative of PanGEO during construction based on actual observed soil conditions. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 11 PanGEO, Inc. During periods of precipitation, the temporary cuts should be protected with plastic sheeting. If areas of seepage are encountered during construction, the slopes may need to be flattened or armored with quarry spalls to reduce the potential of face instability. We recommend that traffic, construction equipment, building materials and excavated soil should not be allowed within a distance equal to one-half the slope height from the top of any excavation, or 3-foot minimum. The setback distance of heavy point loads, such as crane or pump truck outriggers, should be evaluated on a case-by-case basis. Temporary Groundwater Control The contractor should be aware that groundwater seepage is expected in the excavation for the wall foundation, especially during wet times of the year. We anticipate that sumps and pumps will be adequate to dewater the wall footing excavation. STRUCTURAL FILL AND COMPACTION Stuctural fill will be needed next to the wall footing, and may be needed below wall footings if over-excavation of unsuitable soils occurs. Structural fill, should be free of organic and inorganic debris, be near the optimum moisture content and be capable of being compacted to the recommendations provided below. The site soils are relatively fine grained and, in our opinion will not be suitable for re-use as structural fill and an imported structural fill will be needed. Fill for use during wet weather should consist of a well graded soil free of organic material with less than 5 percent fines (silt and clay sized particles passing the U.S. 200 sieve). Structural fill should be moisture conditioned to within about 3 percent of optimum moisture content, placed in loose, horizontal lifts less than 8 inches in thickness, and compacted to at least 95 percent maximum density, determined using ASTM D1557 (Modified Proctor). The procedure to achieve proper density of a compacted fill depends on the size and type of compacting equipment, the number of passes, thickness of the lifts being compacted, and certain soil properties. If the excavation to be backfilled is constricted and limits the use of heavy equipment, smaller equipment can be used, but the lift thickness will need to be reduced to achieve the required relative compaction. Generally, loosely compacted soils are a result of poor construction technique or improper moisture content. Soils with high fines contents are particularly susceptible to becoming too wet Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 12 PanGEO, Inc. and coarse-grained materials easily become too dry, for proper compaction. Silty or clayey soils with a moisture content too high for adequate compaction should be dried as necessary, or moisture conditioned by mixing with drier materials, or other methods. PERMANENT DRAINAGE CONSIDERATIONS Permanent control of surface water should be incorporated in the final grading design. Adequate surface gradients and drainage systems should be incorporated into the design such that surface runoff is directed away from the wall. Under no circumstances should collected surface water be allowed to discharge behind retaining walls. TEMPORARY & PERMANENT EROSION CONTROL CONSIDERATIONS Surface runoff can be controlled during construction by careful grading practices. This may include the construction of shallow, upgrade perimeter ditches or low earthen or asphalt berms to collect runoff and prevent water from entering the excavation. All collected water should be directed to a positive and permanent discharge system such as a storm sewer. It should be noted that the site soils are prone to surficial erosion. Special care should be taken to avoid surface water on open cut excavations, and exposed slopes should be protected with plastic sheeting. Permanent erosion control measures such as covering exposed ground surfaces with topsoil or mulch, and installing landscaping, should be performed as soon as possible after construction to limit the time the exposed surfaces are susceptible to erosion. LIMITATIONS We have prepared this report for use by Kite Realty Group and the project team. Recommendations contained in this report are based on a review of existing data, a site reconnaissance, the results of our limited subsurface exploration program, and our understanding of the project. The study was performed using a mutually agreed-upon scope of work. Variations in soil conditions may exist between the observed soil type and the actual conditions underlying the site. The nature and extent of soil variations may not be evident until construction occurs. If any soil conditions are encountered at the site that are different from those described in this report, we should be notified immediately to review the applicability of our recommendations. Additionally, we should also be notified to review the applicability of our recommendations if there are any changes in the project scope. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 13 PanGEO, Inc. The scope of our work does not include services related to construction safety precautions. Our recommendations are not intended to direct the contractors’ methods, techniques, sequences or procedures, except as specifically described in our report for consideration in design. Additionally, the scope of our work specifically excludes the assessment of environmental characteristics, particularly those involving hazardous substances. We are not mold consultants nor are our recommendations to be interpreted as being preventative of mold development. A mold specialist should be consulted for all mold-related issues. This report may be used only by the client and for the purposes stated, within a reasonable time from its issuance. Land use, site conditions (both off and on-site), or other factors including advances in our understanding of applied science, may change over time and could materially affect our findings. Therefore, this report should not be relied upon after 24 months from its issuance. PanGEO should be notified if the project is delayed by more than 24 months from the date of this report so that we may review the applicability of our conclusions considering the time lapse. It is the client’s responsibility to see that all parties to this project, including the designer, contractor, subcontractors, etc., are made aware of this report in its entirety. The use of information contained in this report for bidding purposes should be done at the contractor’s option and risk. Any party other than the client who wishes to use this report shall notify PanGEO of such intended use and for permission to copy this report. Based on the intended use of the report, PanGEO may require that additional work be performed and that an updated report be reissued. Noncompliance with any of these requirements will release PanGEO from any liability resulting from the use this report. Within the limitation of scope, schedule and budget, PanGEO engages in the practice of geotechnical engineering and endeavors to perform its services in accordance with generally accepted professional principles and practices at the time the Report or its contents were prepared. No warranty, express or implied, is made. Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx 14 PanGEO, Inc. We appreciate the opportunity to be of service to you on this project. Please feel free to contact our office with any questions you have regarding our study, this report, or any geotechnical engineering related project issues. Sincerely, PanGEO, Inc. Jon C. Rehkopf, P.E. Principal Geotechnical Engineer jrehkopf@pangeoinc.com ATTACHMENTS Figures Figure 1 – Vicinity Map Figure 2 – Site and Exploration Plan Appendix A Figure A-1 – Terms and Symbols for Boring and Test Pit Logs Figures A-2 through A-5 – Subsurface Exploration Logs PG-1 through PG-4 Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx PanGEO, Inc. REFERENCES Mullineaux, D.R., 1965, Geologic Map of the Renton Quadrangle, King County, Washington – U.S. Geological Survey Geologic, Quadrangle Map GQ-405, scale 1:24,000. Schuster, J.E., Cabibbo, A.A., Schilter, J.F., and Hubert I.J., 2015, Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington – Washington Division of Geology and Earth Resources, Map Series 2015-03, scale 1:100,000. WSDOT, 2024, Standard Specifications for Road, Bridge and Municipal Construction, M 41-10. Washington Administrative Code (WAC), 2013, Chapter 296-155 - Safety Standards for Construction Work, Part N - Excavation, Trenching, and Shoring, Olympia, Washington. 24-497 Proposed Retaining Wall 17803 108th Avenue SE Renton, Washington 1 VICINITY MAP Figure No.Project No. Fi g 1 - V i c i n i t y M a p . g p j 1 / 1 3 / 2 5 ( 1 0 : 3 1 : 4 4 ) Base Map Credit: King County iMAP. Project Site NOT TO SCALE Project Vicinity Project No.Figure No. SITE AND EXPLORATION PLAN 24-497 2 Fi g 2 - S i t e a n d E x p l o r a t i o n P l a n . g p j 1 / 1 3 / 2 5 ( 1 1 : 0 9 : 3 2 ) J C R 0 20 40 1 inch ~ 40 feet Note: Base map modified from site survey prepared by SAM, dated 5/8/2024. 10 8 t h A V E S E Proposed Retaining Wall 17803 108th Avenue SE Renton, Washington PG-1 PG-2 PG-3 PG-4 LEGEND Approximate Location of Subsurface Explorations (PanGEO, 2024) Approximate Location of Proposed Retaining Wall Limits of Subject Site Limited Geotechnical Report – Proposed Retaining Wall 17803 108th Avenue SE, Renton, WA January 13, 2025 24-497_17803 108th ave se_renton_r_wall.docx PanGEO, Inc. APPENDIX A SUBSURFACE EXPLORATION LOGS MOISTURE CONTENT 2-inch OD Split Spoon, SPT (140-lb. hammer, 30" drop) 3.25-inch OD Spilt Spoon (300-lb hammer, 30" drop) Non-standard penetration test (see boring log for details) Thin wall (Shelby) tube Grab Rock core Vane Shear Dusty, dry to the touch Damp but no visible water Visible free water Terms and Symbols for Boring and Test Pit Logs Density SILT / CLAY GRAVEL (<5% fines) GRAVEL (>12% fines) SAND (<5% fines) SAND (>12% fines) Liquid Limit < 50 Liquid Limit > 50 Breaks along defined planes Fracture planes that are polished or glossy Angular soil lumps that resist breakdown Soil that is broken and mixed Less than one per foot More than one per foot Angle between bedding plane and a planenormaltocoreaxis Very Loose Loose Med. Dense Dense Very Dense SPT N-values Approx. Undrained Shear Strength (psf) <4 4 to 10 10 to 30 30 to 50 >50 <2 2 to 4 4 to 8 8 to 15 15 to 30 >30 SPT N-values Units of material distinguished by color and/orcomposition frommaterial unitsabove andbelow Layers of soil typically 0.05 to 1mm thick, max. 1 cm Layer of soil that pinches out laterally Alternating layers of differing soil material Erratic, discontinuous deposit of limited extent Soil with uniform color and composition throughout Approx. Relative Density (%) Gravel Layered: Laminated: Lens: Interlayered: Pocket: Homogeneous: Highly Organic Soils #4 to #10 sieve (4.5 to 2.0 mm) #10 to #40 sieve (2.0 to 0.42 mm) #40 to #200 sieve (0.42 to 0.074 mm) 0.074 to 0.002 mm <0.002 mm UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP DESCRIPTIONS Notes: MONITORING WELL <15 15 - 35 35 - 65 65 - 85 85 - 100 GW GP GM GC SW SP SM SC ML CL OL MH CH OH PT TEST SYMBOLS 50%or more passing #200 sieve Groundwater Level at time of drilling (ATD)Static Groundwater Level Cement / Concrete Seal Bentonite grout / seal Silica sand backfill Slotted tip Slough <250 250 - 500 500 - 1000 1000 - 2000 2000 - 4000 >4000 RELATIVE DENSITY / CONSISTENCY Fissured: Slickensided: Blocky: Disrupted: Scattered: Numerous: BCN: COMPONENT DEFINITIONS Dry Moist Wet 1. Soil exploration logs contain material descriptions based on visual observation and field tests using a systemmodified from the Uniform Soil Classification System (USCS). Where necessary laboratory tests have beenconducted (as noted in the "Other Tests" column), unit descriptions may include a classification. Please refer to thediscussions in the report text for a more complete description of the subsurface conditions. 2. The graphic symbols given above are not inclusive of all symbols that may appear on the borehole logs.Other symbols may be used where field observations indicated mixed soil constituents or dual constituent materials. COMPONENT SIZE / SIEVE RANGE COMPONENT SIZE / SIEVE RANGE SYMBOLS Sample/In Situ test types and intervals Silt and Clay Consistency SAND / GRAVEL Very Soft Soft Med. Stiff Stiff Very Stiff Hard Phone: 206.262.0370 Bottom of BoringBoulder: Cobbles: Gravel Coarse Gravel: Fine Gravel: Sand Coarse Sand: Medium Sand: Fine Sand: Silt Clay > 12 inches 3 to 12 inches 3 to 3/4 inches 3/4 inches to #4 sieve Atterberg Limit Test Compaction Tests Consolidation Dry Density Direct Shear Fines Content Grain Size Permeability Pocket Penetrometer R-value Specific Gravity Torvane Triaxial Compression Unconfined Compression Sand 50% or more of the coarse fraction passing the #4 sieve. Use dual symbols (eg. SP-SM) for 5% to 12% fines. for In Situ and Laboratory Testslisted in "Other Tests" column. 50% or more of the coarse fraction retained on the #4 sieve. Use dual symbols (eg. GP-GM) for 5% to 12% fines. DESCRIPTIONS OF SOIL STRUCTURES Well-graded GRAVEL Poorly-graded GRAVEL Silty GRAVEL Clayey GRAVEL Well-graded SAND Poorly-graded SAND Silty SAND Clayey SAND SILT Lean CLAY Organic SILT or CLAY Elastic SILT Fat CLAY Organic SILT or CLAY PEAT ATT Comp Con DD DS %F GS Perm PP R SG TV TXC UCC Figure A-1 Project No: 24-497 Project Name: Proposed Retaining Wall Project Loca�on: 17803 108th Ave SE, Renton, Washington Date Excavated: 12/30/2024 24-497 hand boring logs.docx Figure A-2 PanGEO, Inc. Hand Boring Log: PG-1 Approximate ground surface eleva�on: ~390 feet (NAVD 88 ) Approximate Loca�on: 26 feet north of southern rockery, abou t 1’ east of curb at toe of slope Depth (feet ) Material Descrip�on 0 – ½ Loose, moist, dark brown, silty SAND and sandy SILT with some gravel and prevalent organics. [Topsoil] ½ – 1 Loose to medium dense, moist, tan with iron oxide staining, silty SAND with some gravel and trace organics. [Fill] 1 – 2 ½ Washed 7/8-inch diameter rounded drain rock [Fill from apparent drainage system] 2½ Medium dense to dense, silty SAND with some gravel [Glacial Till (Qvt)] - Soil descrip�on based on probing with a ½-inch diameter soil probe through the washed rock. Probe penetra�ons were observed to be less than 2 to 3 inches into the underlying na�ve soil. Photo shows drain rock at ~1 foot below ground surface at bottom of hole. -PG-1 was terminated approximately 2½ feet below ground surface due to caving drain rock. -Light groundwater seepage was observed about 2’ below ground surface. Project No: 24-497 Project Name: Proposed Retaining Wall Project Loca�on: 17803 108th Ave SE, Renton, Washington Date Excavated: 12/30/2024 24-497 hand boring logs.docx Figure A-3 PanGEO, Inc. Hand Boring Log: PG-2 Approximate ground surface eleva�on: ~392 feet (NAVD 88 ) Approximate Loca�on: 28 feet north of southern rockery, abou t 4’ east of curb at toe of slope Depth (feet ) Material Descrip�on 0 – ½ Loose, moist, dark brown, silty SAND and sandy SILT with some gravel and prevalent organics. [Topsoil] ½ - 2 Medium dense to dense, moist, tan with some iron-oxide stains, silty SAND with some gravel [Glacial Till (Qvt)] - Soil probe penetra�on less than 1” into dense silty SAND Photo shows soil sample at ~2 feet below ground surface. -PG-2 was terminated approximately 2 feet below ground surface due to refusal on dense gravelly soils. -No groundwater seepage was observed in test hole. Project No: 24-497 Project Name: Proposed Retaining Wall Project Loca�on: 17803 108th Ave SE, Renton, Washington Date Excavated: 12/30/2024 24-497 hand boring logs.docx Figure A-4 PanGEO, Inc. Hand Boring Log: PG-3 Approximate ground surface eleva�on: ~391 feet (NAVD 88 ) Approximate Loca�on: 20 feet north of former bank sign, about 3’ east of curb at toe of slope Depth (feet ) Material Descrip�on 0 – ½ Loose, moist, dark brown, silty SAND and sandy SILT with some gravel and prevalent organics. [Topsoil] ½ – 2½ Loose to medium dense, moist to wet, tan with iron oxide staining, silty SAND with some gravel and trace organics. [Fill] - Groundwater seepage at 1 foot below ground surface - Some washed rock observed - maybe near drainage line 2½ Medium dense to dense, tan with iron oxide staining, moist to wet, silty SAND with some gravel [Glacial Till (Qvt)] - Soil probe penetra�ons of less than 1 inch @ 2½ feet below ground surface. Photo shows seepage filling hole to about 1 foot below ground surface. -PG-3 was terminated approximately 2½ feet below ground surface due to dense soils and groundwater seepage causing caving of hole. -Heavy groundwater seepage was observed about 1’ below ground surface. Project No: 24-497 Project Name: Proposed Retaining Wall Project Loca�on: 17803 108th Ave SE, Renton, Washington Date Excavated: 12/30/2024 24-497 hand boring logs.docx Figure A-5 PanGEO, Inc. Logged by HKR & JCR Hand Boring Log: PG-4 Approximate ground surface eleva�on: ~395 feet (NAVD 88 ) Approximate Loca�on: 12 feet south of former bank sign, ~12’ east of curb at toe of slope Depth (feet ) Material Descrip�on 0 – 2/3 Loose, moist, dark brown, silty SAND and sandy SILT with some gravel and prevalent organics. [Topsoil] 2/3 – 2 Loose to medium dense, moist, medium to dark brown, sandy SILT with trace gravel and trace to some organics. [Fill] 2 - 4½ Medium dense to dense, moist, tan with heavy iron-oxide stains, silty SAND with some gravel [Glacial Till (Qvt)] - Soil probe penetra�ons about 2” @ 2 feet depth - Gravel content increases around a depth of about 4 feet - Soil probe penetra�on less than 1” @ 4½ feet depth Photo shows soil sample at ~2½ feet below ground surface. -PG-4 was terminated approximately 4½ feet below ground surface due to refusal on dense gravelly soils. -No groundwater seepage was observed in test hole.