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HomeMy WebLinkAboutRS_Geotechnical_Report_v11 Geotechnical Report 10814 SE 173rd St. Renton Report Date: 12/9/2015 2 Dear Client, As requested, we have conducted a geotechnical soil investigation for 10814 SE 173rd St. Renton concerning soil permeability and classification. Our findings and design criteria are enclosed. We trust the information provided is sufficient for your current needs. If you have any questions please contact us. Regards, Cash M. Carr PE. 3 Subsurface Exploration and Geotechnical Engineering Study Regarding: Soil Permeability Introduction This report presents the results of our subsurface investigation and geotechnical report for the residence located at 10814 SE 173rd St. Renton in regards to soil permeability. Purpose and Scope This subsurface investigation and geotechnical report is intended to determine and present our finding for soil permeability and recommend procedures for infiltration. Limitations The scope of this report is limited to drainage. Structural and bearing considerations have not been included in the scope of this report. Field Explorations A geotechnical borehole was constructed to a depth of 4’, a depth which is sufficient for determining the capacity for storm water infiltration from the surface. Test was performed by professional engineer Cash M. Carr and geologist Jackie Perkins. Disturbed samples were taken at the lowest point on the property, as in our judgment, this point will be the worst case for runoff saturation. Sampling was performed by professional engineer Cash M. Carr and geologist Jackie Perkins. Our sample log is presented below. Laboratory Testing This grain size analysis sampled four feet of soil from the site at 10814 SE 173 St, Renton. Samples were obtained on site, where initial observations were recorded. The samples were dried for five days before being processed through 10, 20, 40, 60, 80, and 100 sieves. 4 RESULTS: Foot 1 Initial observations: extremely organically rich, very dark brown, moderate moisture content, grains are rounded and range 0.2 -3.0mm with occasional fine gravel. Starting weight: 5.4 oz* Sieve Weight (oz) Percent wt % Passing 10 1.9 36.5 63.5 20 1.1 21.2 42.3 40 1.8 34.6 7.7 60 0.3 5.77 1.92 80 0.05 0.96 0.96 100 0.05 0.96 0.00 Total: 5.2 D10= 0.35 D30= 0.65 D60= 1.7 Cu= 4.86 Cc= 0.710 * Ounces were used in this procedure as the available scale did not produce decimals for grams. Particle size distribution curve for foot 1: 5 Foot 2 Initial observations: some organic material, moderately moist, dark brown, fine sand with silt and some gravel, small grains are clumping together. Starting weight: 6.1oz Sieve Weight (oz) Percent wt % Passing 10 2.4 40.0 60.0 20 1 16.7 43.3 40 2.3 38.3 5.0 60 0.2 3.33 1.67 80 0.05 0.83 0.83 100 0.05 0.83 0.00 Total: 6.0 D10= 0.47 D30= 0.55 D60= 2 Cu= 4.255 Cc= 0.322 6 Particle size distribution curve for foot 2: 7 Foot 3 Initial observations: moderately moist, dark/medium orange brown, coarse sand and fine gravel with some fine sand, a few very coarse gravel clasts (bordering on small cobbles) approximately 4cm diameter, smaller grains clumping together from moisture. Starting weight: 5.9 Sieve Weight (oz) Percent wt % Passing 10 2.3 39.7 60.3 20 1.2 20.7 39.7 40 1.9 32.8 6.9 60 0.3 5.2 1.7 80 0.05 0.9 0.9 100 0.05 0.9 0.0 Total: 5.8 D10= 0.46 D30= 0.59 D60= 2 Cu= 4.35 Cc= 0.378 Particle size distribution curve for foot 3: 8 Foot 4 Initial observations: Organically rich, dark orange brown, fine gravels with sand and silt, some medium gravel clasts, finer grains clump together due to moisture. Starting weight: 7.9 Sieve Weight (oz) Percent wt % Passing 10 3.4 43.6 56.4 20 1.1 14.1 42.3 40 2.5 32.1 10.3 60 0.7 9.0 1.3 80 0.05 0.6 0.6 100 0.05 0.6 0.0 Total: 7.8 D10= 0.425 D30= 0.63 D60= 2 Cu= 4.71 Cc= 0.467 9 Particle size distribution curve for foot 4: 10 DATA ANALYSIS Each of the samples yielded uniformity coefficients <6 and coefficients of gradation <1, categorizing the soil as poorly graded gravelly sand (SP) under the grading criteria of the Unified Soil Classification System. The top foot of soil may also be considered peat (PT) due to high organic content, dark brown to black color, and fibrous texture. The soil is overall texturally classified as loamy sand with gravel. SOURCES OF ERROR Several sources of error arose from the available equipment. The sieve with the largest diameter mesh (no. 10) would only allow particles smaller than 2mm to pass through, which fails to allow for distinction between coarse sand grains and gravels. This may cause the soil to be classified as more poorly graded than it truly is. The presence of gravels and small cobbles in the soil should be taken into account for the purpose of geoengineering, however the majority of the soil is comprised of sand. For each sample the weight of the soil retained by the 80 and 100 sieves were between 0 and 0.1 ounces. For each of these measurements 0.05oz was recorded in order to maintain that this particle size was present in the sample, however never greater than 1% by weight. Soil samples were tested for permeability by spreading a ½” layer of soil from each sample across a #80 mesh sieve. Soils were weted to saturation prior to saturation as permeability was significantly higher in dry soil. The fully saturated condition tested represents worst case permeability. PERMABILITY TESTING Sample 1 Sample 2 Sample 3 Average Soil Sample Thickness (in) 0.5 0.5 0.5 Time (s) 31 29 31 h1 (water column height start) 1 1 1 h2 (water column height end) 0.5 0.5 0.5 K (in/s) 0.012138306 0.012975 0.012138 K (in/hr) 44 47 44 45 11 VICINITY MAP TEST SITE ON SOUTH SIDE OF RESIDENCE 12 Summary of Test Results BOREHOLE 1 LOCATION: 44’ NORTH OF C.L. OF SE 173st, 22’ EAST OF WEST PROPERTY LINE. 0 2’ Extremely organic, rich, very dark brown, moderate moisture content, grains are rounded and range 0.2 -3.0mm with occasional fine gravel TERMINATION OF TEST SAMPLE 4 SAMPLE 2 SAMPLE 1 1’ 3’ 4’ SAMPLE 3 Some organic material, moderately moist, dark brown, fine sand with silt and some gravel, small grains are clumping together. Moderately moist, dark/medium orange brown, coarse sand and fine gravel with some fine sand, a few very coarse gravel clasts (bordering on small cobbles) approximately 4cm diameter, smaller grains clumping together from moisture. Organic, rich, dark orange brown, fine gravels with sand and silt, some medium gravel clasts, finer grains clump together due to moisture. 13 Conclusions We have determined that the site is constructed upon a silt. We have furthermore calculated that your soil has a permeability of 45 inches/hour. Hardpan was not detected to the limits of the test dept. Soils can generally and conservatory be classified as sandy loam due to the large amounts of organics present and generally coarse grained nature of the soil. A limited infiltration system is recommended for this site. A trench length of 125’ is recommend for this site.