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HomeMy WebLinkAboutGeotech Report - InfilltrationPage 1 Cascade GeotechNW 4957 Lakemont Blvd SE C-4, #325 Bellevue, WA 98006 November 4, 2016 File No. 201614 Mr. Wentian Lan 17630 - 108th Avenue SE Renton, WA 98055 Subject: Infiltration Evaluation Proposed Development Infiltration Assessment 17630 - 108th Avenue SE, Renton, WA Dear Mr. Lan, As requested, PanGEO conducted field infiltration testing to evaluate infiltration characteristics at the above site in the City of Renton, Washington. The following sections documents the field infiltration testing procedure, the measured field infiltration rates, subsurface conditions encountered at the test locations, and the recommended long- term (design) infiltration rate. SITE DESCRIPTION AND PROJECT UNDERSTANDING The subject site is located at 17630 – 108th Avenue SE in the City of Renton, Washington (see Vicinity Map, Figure 1). The site is bounded by 108th Avenue SE on the west, by 109th Avenue SE on the east, by a commercial building on the north, and by commercial and residential buildings on the south (see Site and Exploration Plan, Figure 2). The site is currently occupied by a one-story building surrounded by asphalt pavement and landscaping. The site is practically flat. Based on information provided to us, we understand that you plan to remodel and expand the existing building. We also understand that the current drainage design will include new permeable asphalt pavement and a detention tank. As such, evaluation of infiltration feasibility of the on-site soils and infiltration rates is needed for the drainage design. Infiltration Evaluation Proposed Additions: 17630 – 108th Avenue SE, Renton, WA November 4, 2016 201614 17630 108th Ave SE Infiltration Rpt Page 2 PanGEO, Inc. SUBSURFACE EXPLORATIONS Three Pilot infiltration tests (PIT-1 through PIT-3) were conducted on October 28, 2016, to measure field infiltration rates at the site. The infiltration test pits were excavated with hand tools. Additionally, three test pits (TP-1 through TP-3) were excavated on November 3, 2016 to further explore soil conditions beneath the infiltration pit depth with a backhoe. The approximate test locations were measured from existing structures and site features (Figure 2). The test pits were excavated to about 7 feet below existing ground surface and the infiltration test was completed at 2 feet depth. An engineer from Cascade GeotechNW was present during the field explorations to observe the test excavations and to describe and document the soils encountered in the explorations. Summary logs of the test pit excavations are included in the Appendix A to provide descriptions of the materials encountered, depths to soil contacts, and depths of seepage or caving, if present, observed in the test excavation sidewalls. 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, probing the sidewalls with a ½- inch diameter steel rod, and the stability of the test excavation sidewalls. Where soil contacts were gradual or undulating, the average depth of the contact was recorded in the log. After each test pit was completed, the excavation was backfilled with the excavated soils and the surface was tamped and re-graded smooth. IN-SITU INFILTRATION TESTING PROCEDURE An engineer from Cascade GeotechNW conducted the field infiltration tests. The infiltration tests were performed in general accordance with the guidelines of the King County, Washington, Surface Water Design Manual Reference 6-A: Single-Ring Percolation Test Procedure. The test results are summarized in Table 1 on pages 3 and 4. The test locations were selected based the input from the civil engineer, site conditions, and the proposed drainage design. The approximate locations of the infiltration tests are shown on Figure 2. The infiltration testing consisted of excavating to approximately 2 feet below existing grade, initially pre-socked overnight, then placing a 3-foot diameter ring at the bottom of the excavation, seating the ring into the ground on the testing day. Water levels were measured using a measuring tape with 1/16 inch increments. Plate 1 on page 3 shows the Infiltration Evaluation Proposed Additions: 17630 – 108th Avenue SE, Renton, WA November 4, 2016 201614 17630 108th Ave SE Infiltration Rpt Page 3 PanGEO, Inc. general infiltration test setup. As per the test requirements, the ring was filled with water and a constant head of approximately 6 inches was maintained for a 4 hour pre- soaking period on the test day. Following the 4-hour pre-soak period, the water is turned off and the head is allowed to drop for 30 minutes. After 30 minutes, the change in water level is recorded and the ring is refilled to 6 inches depth. This procedure is repeated until consecutive measurements vary by no more than 1/16 inch. The field infiltration rate is then calculated based on the final measured water level drop. SUBSURFACE CONDITIONS The test pits generally encountered 0.5 to 1 foot of brown, loose, very moist, silty sand silt (Topsoil). Below the topsoil, approximately 1 to 1.5 feet of gray, loose, very moist, fine to medium sand was encountered. Below the gray sand layer, the test pits encountered brown-gray, moist to very moist, medium dense to dense, silty sand that extended to the bottom of the test pits at 7 feet below the surface. No groundwater was observed in the test pit at the time of excavation. IN-SITU INFILTRATION TEST RESULTS Infiltration testing data and results are summarized in Table 1 below. Table 1 – Summary of Field Infiltration Test Data Time Head Loss (Inches) Percolation Rate (Minutes/Inch) PIT -1 11:45-12:15 11/16 43.6 12:15-12:45 10/16 48.0 12:45-13:15 9/16 53.3 Plate 1 – Infiltration test set-up at PIT-3 Infiltration Evaluation Proposed Additions: 17630 – 108th Avenue SE, Renton, WA November 4, 2016 201614 17630 108th Ave SE Infiltration Rpt Page 4 PanGEO, Inc. 13:15-13:45 9/16 53.3 13:45-14:15 9/16 53.3 14:15-14:45 9/16 53.3 PIT -2 11:50-12:20 12/16 40.0 12:20-12:50 11/16 43.6 12:50-13:20 10/16 48.0 13:20-13:50 10/16 48.0 13:50-14:20 10/16 48.0 14:20-14:50 10/16 48.0 PIT -3 12:00-12:30 10/16 48.0 12:30-13:00 9/16 53.3 13:00-13:30 8/16 60.0 13:30-14:00 8/16 60.0 14:00-14:30 8/16 60.0 14:30-15:00 8/16 60.0 Infiltration Evaluation Proposed Additions: 17630 – 108th Avenue SE, Renton, WA November 4, 2016 201614 17630 108th Ave SE Infiltration Rpt Page 5 PanGEO, Inc. The last water level drop is used to calculate the field percolation rate. Based on three infiltration tests, it is our opinion that a percolation rate of 60.0 minutes/inch may be conservatively used. This percolation rate is equivalent to an infiltration rate of 1.0 inches/hour. For design purposes, the field infiltration rates must be reduced through correction factors, as discussed in the following section. DESIGN INFILTRATION RATE The infiltration rates measured in the field should be reduced through correction factors to account for uncertainties in the test method used, depth to the water table or impervious strata, the geometry of the infiltration facility, and degree of influent control to prevent siltation and bio-buildup. The simplified method outlined in the King County Surface Water Design Manual (KCSWDM, 2009) was used to estimate the maximum design infiltration rate. The simplified method equation is provided below: Idesign = Imeasured x Ftesting x Fgeometry x Fplugging (KCSWDM Eq 5-11) The following values were used to conservatively reduce the field infiltration rate: Imeasured = 1.0 inches per hour Ftesting = 0.35 (for small-scale testing) Fgeometry = 1 (D=3 feet, W=3 feet) Fplugging = 0.9 (for medium sands) Therefore, we conservatively recommend a long-term (design) infiltration rate of 0.315 inches per hour for the proposed permeable pavement design. The infiltration testing was performed at approximately 2 feet. For design purpose, the design infiltration trench depth should be at 1.5-2 feet below the existing grade. LIMITATIONS This report has been prepared for the exclusive use of Mr. Wentian Lan and his other consultants for specific application to the proposed development. This report is intended to provide infiltration feasibility and recommendations based on a site reconnaissance, field infiltration testing, and our understanding of the project. The study was performed using a mutually agreed-upon scope of work. Infiltration Evaluation Proposed Additions: 17630 – 108th Avenue SE, Renton, WA November 4, 2016 201614 17630 108th Ave SE Infiltration Rpt Page 6 PanGEO, Inc. Variations in soil conditions may exist between the locations of the explorations 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. 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 has been prepared for planning and design purposes for specific application to the proposed project in accordance with the generally accepted standards of local practice at the time this report was written. No warranty, express or implied, is made. 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. Cascade Group 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 Cascade GeotechNW of such intended use and for permission to copy this report. Based on the intended use of the report, Cascade GeotechNW may require that Infiltration Evaluation Proposed Additions: 17630 – 108th Avenue SE, Renton, WA November 4, 2016 201614 17630 108th Ave SE Infiltration Rpt Page 7 PanGEO, Inc. additional work be performed and that an updated report be reissued. Noncompliance with any of these requirements will release Cascade Group from any liability resulting from the use this report. CLOSURE We appreciate the opportunity to be of service and trust that the information outlined in this letter meets your need at this time. Please call if you have any questions. Sincerely, H. Michael Xue, P.E. Principal Geotechnical Engineer Enclosures: Figure 1 Vicinity Map Figure 2 Site and Exploration Plan Appendix A Summary Test Pit Logs A-1 thr. A-3 Logs of Test Pits TP-1 through TP-3 Infiltration Evaluation Proposed Additions: 17630 – 108th Avenue SE, Renton, WA November 4, 2016 201614 17630 108th Ave SE Infiltration Rpt Page 8 PanGEO, Inc. REFERENCES: Booth, D. B., Troost, K. A., and Wisher, A. P., 2007, The Geologic Map of King County, Washington: scale 1:100,000. King County Department of Natural Resources and Parks, Surface Water Design Manual, 2009. Figure No.Project No.201614 Infiltration Evaluation 17630 - 108th Avenue SE Renton, Washington 1file.grf w/ file.dat 11/4/16 (10:18) SDDBase Map: Google Maps VICINITY MAP SITE Cascade GeotechNW Not to Scale Infiltration Evaluation17630 - 108th Avenue SERenton, WashingtonSITE AND EXPLORATIONS PLAN2016142Original Contours.grf 11/4/16 (11:20) AAEProject No. Figure No.Note:Basemap modified from Civil Utility Plan prepared by Tatu Consulting Engineers dated July 2016.Approx. PIT LocationApprox. Test Pit LocationLegend:Appro. Scale:1" = 30'TP-3TP-2TP-3PIT-1TP-1PIT-3PIT-2PIT-1Cascade GeotechNW APPENDIX A SUMMARY TEST PIT LOGS 201614 17630 108th Ave SE Infiltration Rpt Page A-1 Cascade GeotechNW Test Pit TP-1 Approximate ground surface elevation: N/A Ground Surface Conditions: Bark Depth (ft) Material Description 0 – 1 Loose, brown-dark brown, silty SAND (SM), very moist (Topsoil) 1 - 2 Loose, gray, fine to medium SAND (SP), very moist 2 – 7 Medium dense to dense, brown, silty SAND (SM), trace gravel, moist to very moist Test Pit terminated approximately 7 feet below ground surface. No caving and groundwater/seepage observed in the test pit. 201614 17630 108th Ave SE Infiltration Rpt Page A-2 Cascade GeotechNW Test Pit TP-2 Approximate ground surface elevation: N/A Ground Surface Conditions: Grass Depth (ft) Material Description 0 – 0.5 Loose, brown, silty SAND (SM), trace roots, very moist (Topsoil) 0.5 - 2 Loose, gray, fine to medium SAND (SP), very moist 2 – 7 Medium dense to dense, brown-gray, silty SAND (SM), trace gravel, moist to very moist Test Pit terminated approximately 7 feet below ground surface. No caving and groundwater/seepage observed in the test pit. 201614 17630 108th Ave SE Infiltration Rpt Page A-3 Cascade GeotechNW Test Pit TP-3 Approximate ground surface elevation: N/A Ground Surface Conditions: Grass Depth (ft) Material Description 0 – 1 Loose, brown-dark brown, silty SAND (SM), trace roots, very moist (Topsoil) 1 - 2 Loose, gray, fine to medium SAND (SP), very moist 2 – 7 Medium dense to dense, gray-brown, silty SAND (SM), trace gravel, moist to very moist Test Pit terminated approximately 7 feet below ground surface. No caving and groundwater/seepage observed in the test pit. Date Test Pits Excavated: November 3, 2016 Test Pits Logged by: HX N ( blows/ft ) Approximate Consistency N (blows/ft ) Approximate Relative Density (%) Undrained Shear Strength (psf) 0 to 4 0 - 15 Very Soft 0 to 2 < 250 5 to 10 16 - 35 Soft 3 to 4 250 - 500 11 to 30 36 - 65 Medium Stiff 5 to 8 501 - 1000 31 to 50 66 - 85 Stiff 9 to 15 1001 - 2000 over 50 86 - 100 Very Stiff 16 to 30 2001 - 4000 Hard over 30 > 4000 CASCADE GEOTECHNW Project No. 201612 Figure A-4 KEY: Indicates 3-inch OD Dames & Moore Sample. Indicates 2-inch OD Split Spoon Sample (SPT). Indicates Disturbed Sample. Indicates No Recovery. Indicates Bag Sample. Indicates Shelby Tube Sample. COMPONENT DEFINITIONS COMPONENT SIZE RANGE Boulders CobblesGravel Coarse gravel Fine gravel Sand Coarse sand Medium sand Fine sand Silt and Clay Larger than 12 in 3 in to 12 in 3 in to No 4 (4.5mm ) 3 in to 3/4 in 3/4 in to No 4 ( 4.5mm )No. 4 ( 4.5mm ) to No. 200 ( 0.074mm ) No. 4 ( 4.5 mm ) to No. 10 ( 2.0 mm ) No. 10 ( 2.0 mm ) to No. 40 ( 0.42 mm ) No. 40 ( 0.42 mm ) to No. 200 ( 0.074 mm ) Smaller than No. 200 ( 0.074 mm ) DESCRIPTIVE TERMS RANGE OF PROPORTION Trace or little Some Clayey, silty, sandy, gravellyAnd 1 - 5% 6 - 12% 13 - 30% 31 - 50% COMPONENT PROPORTIONS MOISTURE CONTENT DRY DAMP MOIST WET Absence of moisture, dusty, dry to the touch.Some perceptible moisture; below optimum No visible water; near optimum moisture content Visible free water, usually soil is below water table. RELATIVE DENSITY OR CONSISTENCY VERSUS SPT N -VALUE COHESIONLESS SOILS COHESIVE SOILS Density Very Loose Loose Medium Dense Dense Very Dense ATD: At Time of Drilling BGS: Below Ground Surface MAJOR DIVISION GRAPHIC LETTER TYPICAL DESCRIPTIONS SYMBOL SYMBOL WELL-GRADED GRAVELS, GRAVEL- SAND MIXTURES, LITTLE OR NO FINESGW GP POORLY-GRADED GRAVELS,GRAVEL-SAND MIXTURES, LITTLE OR NO FINES GM SILTY GRAVELS, GRAVEL-SAND- SILT MIXTURES GC CLAYEY GRAVELS, GRAVEL-SAND- CLAY MIXTURES CLEAN GRAVELS (LITTLE OR NO FINES) GRAVELS WITH FINES (APPRECIABLE AMOUNT OF FINES) CLEAN SAND (LITTLE OR NO FINES) SANDS WITH FINES (APPRECIABLE AMOUNT OF FINES) SW SP SM SC WELL-GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES SILTY SANDS, SAND-SILT MIXTURES CLAYEY SANDS, SAND-CLAY MIXTURES ML CL OL MH CH OH PT SILTS AND CLAYS LIQUID LIMIT LESS THAN 5O SILTS AND CLAYS LIQUID LIMIT GREATER THAN 5O INORGANIC SILTS AND VERY FINESANDS, ROCK FLOUR, SILTY ORCLAYEY FINE SANDS OR CLAYEYSILTS WITH SLIGHT PLASTICITY INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTYCLAYS, LEAN CLAYS ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS FINE SAND OR SILTY SOILS INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS ORGANIC CLAYS OF MEDIUM TOHIGH PLASTICITY, ORGANIC SILTS PEAT, HUMUS, SWAMP SOILS WITH HIGH ORGANIC CONTENTSHIGHLY ORGANIC SOILS NOTE: DUAL SYMBOLS ARE USED TO INDICATE BORDERLINE SOIL CLASSIFICATIONS UNIFIED SOIL CLASSIFICATION SYSTEM GRAVEL AND GRAVELLY SOILS MORE THAN 50% OF COARSE FRACTION RETAINED ON NO. 4 SIEVE COARSE GRAINED SOILS MORE THAN 50% OF MATERIAL IS LARGER THAN NO. 200 SIEVESIZE MORE THAN 50% OF COARSE FRACTION PASSING NO. 4 SIEVE SAND AND SANDY SOILS FINE GRAINED SOILS MORE THAN 50% OF MATERIAL IS SMALLER THAN NO. 200 SIEVE SIZE POORLY-GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES CASCADE GEOTECHNW Project No. 201614 Figure A-5