The URL can be used to link to this page

Home My WebLink AboutRS_Geotechnical_Report_170605_V1 ________________________________________________ 3213 Eastlake Ave E Ste B Seattle, WA 98102 T. (206) 262-0370 F. (206) 262-0374 Geotechnical & Earthquake Engineering Consultants August 25, 2016 File No. 16-204 Ms. Tatiana Gershanovich Sound Housing, LLC 8005 5th Ave, Suite 101-500 Seattle, WA 98104 Subject: Geotechnical Evaluation for Stormwater Drainage Design Proposed Short-Plat and Development 3302 Burnett Avenue North, Renton, Washington Dear Ms. Gershanovich, As requested, PanGEO completed a geotechnical evaluation to assist you with the stormwater drainage design at the above referenced property. We understand that the proposed development consists of subdividing the property into two single-family residential lots, and to construct one single family residence on each subdivided lot (see Figures 1 and 2). We also understand that the current stormwater drainage design includes a ten-foot long perforated pipe which will be connected to an existing catch basin in the city right of way for each parcel. We further understand that a geotechnical evaluation is required by the City of Renton to evaluate the groundwater and soil conditions for the proposed flow control and BMP design. Our service scope consisted of reviewing readily-available geologic and geotechnical data, observing excavations of three test pits, logging the soil conditions, and summarizing the test results. SUBSURFACE EXPLORATION AND CONDITIONS CURRENT EXPLORATION On July 10, 2016, three test pits were excavated at the subject property. The test pits were completed to the maximum depths of five to six feet below the existing ground surface. After each test pit was logged, the excavation was backfilled with the excavated soils and the surface was tamped and re-graded smooth. Geotechnical Evaluation for Stormwater Drainage Design Proposed Short-Plat and Development: 3302 Burnett Avenue N, Renton, WA August 25, 2016 16-204 3302 Burnett Ave N Rpt PanGEO, Inc. 2 A geologist from PanGEO was present during the field exploration to observe the test pit excavations, obtain representative soil samples, and describe and document the subsurface conditions encountered. The system used to classify the soils is summarized on Figure A-1, Terms and Symbols for Boring and Test Pit Logs. The relative in-situ density of cohesionless soils, or the relative consistency of fine-grained soils, was estimated from the excavating action of the excavator, and the stability of the test pit sidewalls. Summary test pit logs are presented in Appendix A. The logs provide descriptions of the materials encountered, depths to soil contacts, and depths of seepage or caving, if present, observed in the test pit sidewalls. In general, the soils encountered at the test pit locations consisted of a surficial topsoil layer over approximately two feet of dense, grey-brown, silty sand with gravel (weathered till) which became very dense and cemented at depth (glacial till, or hardpan). No groundwater was present at the time of excavation. However, the contractor should also be aware that groundwater levels will fluctuate depending on the season, precipitation, and the surface water level in Lake Washington. Generally, the water level is higher and seepage rates are greater in the wetter, winter months (typically October through May). PREVIOUS EXPLORATIONS As part of our study, we also reviewed the results of previous explorations conducted in the project vicinity to gain an understanding of the subsurface conditions in the area. Specificall y, the summary logs of test borings from the following previous explorations were reviewed:  Summary Test Borings B-10, B-23, and B-24, Hydrogeologic Report for Proposed Kennydale Tunnel, prepared by Robertson & Roberts, 1961 The approximate locations of these previous test borings and their summary logs are included in Appendix B for reference. In summary, the previous exploration encountered about 50 feet of glacial till at B-23 (the boring nearest the subject property) and B-24 (downslope from subject property), and about 10 feet of recessional outwash overlying 60 feet of glacial till at B-10 (upslope from subject property). Geotechnical Evaluation for Stormwater Drainage Design Proposed Short-Plat and Development: 3302 Burnett Avenue N, Renton, WA August 25, 2016 16-204 3302 Burnett Ave N Rpt PanGEO, Inc. 3 OPTIONS AND CONCLUSIONS The subject property is underlain by glacial till (Hardpan) at shallow depths. As a result, stormwater disposal using infiltration is not feasible. Based on the Storm Drainage Small Site Technical Information Report (Anstey Engineering, 2015), the current drainage design consisted of a perforated pipe section in a minimum 2 feet wide and 10 feet long gravel trench at least 18 inches deep. The perforated pipe is connected to the existing catch basin in the right of way. Based on the surface and subsurface conditions at the site, the current drainage design is considered appropriate from a geotechnical engineering standpoint. It is also our opinion that the current drainage design will not have adverse impacts of the site stability of the subject and surrounding properties. LIMITATIONS We have prepared this report for use by Ms. Tatiana Gershanovich. Recommendations contained in this report are based on a site reconnaissance, a subsurface exploration program, review of pertinent subsurface information, and our understanding of the project. The study was performed using a mutually agreed-upon scope of work. 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. 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. 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. Geotechnical Evaluation for Stormwater Drainage Design Proposed Short-Plat and Development: 3302 Burnett Avenue N, Renton, WA August 25, 2016 16-204 3302 Burnett Ave N Rpt PanGEO, Inc. 4 Sincerely, Bart Weitering, G.I.T. H. Michael Xue, P.E. Staff Geologist Senior Geotechnical Engineer Enclosures: Figure 1 Vicinity Map Figure 2 Site and Exploration Plan Appendix A: Summary Test Pit Logs Figure A-1 Terms and Symbols for Boring and Test Pit Logs Figure A-2 Log of Test Pit TP-1 Figure A-3 Log of Test Pit TP-2 Figure A-4 Log of Test Pit TP-3 Appendix B: Previous Subsurface Explorations Figure B-1 Previous Boring Locations Figure B-2 Cross Section with Logs of Borings B-10, B-23, and B-24 Geotechnical Evaluation for Stormwater Drainage Design Proposed Short-Plat and Development: 3302 Burnett Avenue N, Renton, WA August 25, 2016 16-204 3302 Burnett Ave N Rpt PanGEO, Inc. 5 REFERENCES: Anstey Engineering, Storm Drainage Small Site Technical Information Report – Proposed Two Lot Short Plat Located at 3302 Burnett Avenue North, Renton, Washington 98055, November 25, 2015. City of Renton Department of Community and Economic Development Planning Division, Pre- Application Meeting Comments for 3302 Kennydale Short Plat, Pre 15-000530, July 30, 2015. Roberts & Robertson, Summary Test Pit Logs, B-10, B-23, and B-24, Hydrogeologic Report for Proposed Kennydale Tunnel, Burnett Avenue N, Renton, Washington, October 30, 1961. 16-204 Proposed Short-Plat and Development 3302 Burnett Avenue N Renton, Washington 1 VICINITY MAP BH-1 Figure No.Project No. Reference: Google Terrain Map Project Site Not to Scale Figure No.Project No.16-204 2 Proposed Short-Plat and Development 3302 Burnett Avenue N Renton, Washington SITE AND EXPLORATION PLAN Note: Basemap modified from Tree Replacement Plan by GHA Landscape Architects, stamp dated February 11, 2016. Approx. Scale 1" = 20' Test Pit Location Legend: Approx. Outline of Proposed Development PG-1 North Lot Middle Lot South Lot PIT-1 133rd Ave NE TP-1 TP-2 TP-3 APPENDIX A SUMMARY TEST PIT 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 planenormal to core axis 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 from material units above and below 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 $LOG KEY 13-104_LOGS.GPJ PANGEO.GDT 6/18/13APPENDIX A Figure A-2 Test Pit No. TP-1 Approximate ground surface elevation: 86 Approximate location (WGS84): 47.52104, -122.20683 Depth (ft) USCS Material Description 0 – 2 SM/ML Grass and sod over medium dense, dark brown, slightly organic silty fine SAND/sandy SILT with trace gravel (SM/ML); dry to moist; poorly graded, roots [Topsoil] 2 – 4 SP-SM Dense, light grey-brown to orange-brown, slightly silty, gravelly fine SAND (SP-SM); dry to moist; poorly graded, iron-oxide staining [Weathered Till] 4 – 6 SM Very dense, olive brown, silty, gravelly fine SAND (SM); moist; poorly graded, cemented, cobbles up to one foot in diameter [Glacial Till] Plate 1 at right shows TP-1 at approximately 6-feet in depth TP-1 was terminated approximately 6 feet below ground surface. Groundwater seepage was not observed. APPENDIX A Figure A-3 Test Pit No. TP-2 Approximate ground surface elevation: 84 Approximate location (WGS84): 47.52124, -122.20690 Depth (ft) USCS Material Description 0 – ½ SM Grass and sod over medium dense, brown, silty fine SAND with trace gravel (SM); dry to moist; poorly graded, roots [Topsoil] ½ – 2 SM Dense, light grey-brown, silty, gravelly fine SAND (SM); dry to moist; poorly graded, trace iron-oxide staining, weakly cemented [Weathered Till] 2 – 5½ SM Very dense, olive brown to mottled red-brown, silty, gravelly fine SAND (SM); moist; poorly graded, cemented, cobbles up to six inches in diameter [Glacial Till] Plate 2 at right shows TP-2 at approximately 5½ feet in depth. TP-2 was terminated approximately 5½ feet below ground surface. Groundwater seepage was not observed. APPENDIX A Figure A-4 Date of Test Pit excavations: August 10, 2016 Test Pits Logged by: B. Weitering Test Pit No. TP-3 Approximate ground surface elevation: 84 Approximate location (WGS84): 47.52128, -122.20670 Depth (ft) USCS Material Description 0 – 1 SM/ML Grass and sod over medium dense, dark brown, slightly organic silty fine SAND/sandy SILT with trace gravel (SM/ML); dry to moist; poorly graded, roots [Topsoil] 1 – 3½ SM Dense, light grey-brown, silty, gravelly fine SAND (SM); dry to moist; poorly graded, trace iron-oxide staining, weakly to moderately cemented [Weathered Till] 3½ – 5 SP-SM Dense, grey-brown to red-brown, slightly silty, fine SAND with trace gravel (SP-SM); moist; poorly graded, iron-oxide staining [Glacial Till] Plate 3 at right shows TP-3 at Approximately 5 feet in depth. TP-3 was terminated approximately 5 feet below ground surface. Groundwater seepage was not observed. APPENDIX A APPENDIX B PREVIOUS SUBSURFACE EXPLORATIONS Project No.Figure No.16-204 B-1 16-153 Fig 2 Site Exploration Plan.grf 8/24/16 (13:47) NER Proposed Short-Plat and Development 3302 Burnett Avenue N Renton, Washington LEGEND: PREVIOUS BORING LOCATIONS Carleton Ave SouthApprox. Scale 1" = 300' Parcel A 84 80 Property L i n e (Elevation) 84 16th Avenue S Proposed 3-Story Rowhouse Proposed 3-Story Townhouses 90 82 78 Parcel B 82 Existing Residential Buildings to be Removed 84 86 AlleyTP-1 IT-1 TP-1 TP-2TP-3 TP-4 B-2A B-2B B-3 B-4 N Project Site B-24 B-23 B-10 Approximate Location of Previous Test Borings (Robertson & Roberts, 1961) Reference: King County iMap Proposed Short-Plat and Development 3302 Burnett Avenue N Renton, Washington Cross Section with Logs of Previous Test Borings B-10, B-23, and B-24 16-204 Figure B-216-204file.grf w/ file.dat 8/24/16 (14:21) TEA2Project No.Figure No. Legend: Approximate Location of Subject Property along Cross-Section Note: Figure modified from Cross Section by Robertson & Roberts dated October 30, 1961