1023 100TH ST SW Geotech Report 2022-10-25

COBALT GEOTECHNICAL INVESTIGATION GEOSCIENCES EVERETT, WASHINGTON December 3,2019 For shallow foundation support, we recommend widths of at least i6 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed structure. Provided that the footings are supported as recommended above, a net allowable bearing pressure of 2,50o pounds per square foot(psf)maybe used for design. A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing excavations should be inspected to verify that the foundations will bear on suitable material. Exterior footings should have a minimum depth of i8 inches below pad subgrade (soil grade) or adjacent exterior grade,whichever is lower. Interior footings should have a minimum depth of 12 inches below pad subgrade(soil grade)or adjacent exterior grade,whichever is lower. If constructed as recommended, the total foundation settlement is not expected to exceed r inch. Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most settlement is expected to occur during construction, as the loads are applied. However, additional post-construction settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be observed by a qualified geotechnical consultant. Resistance to lateral footing displacement can be determined using an allowable friction factor of o.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds per cubic foot(pcf) acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior areas). The allowable friction factor and allowable equivalent fluid passive pressure values include a factor of safety of 1.5. The frictional and passive resistance of the soil may be combined without reduction in determining the total lateral resistance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing excavations, should be removed prior to placing concrete. The potential for wetting or drying of the bearing materials can be reduced by pouring concrete as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. 8.1.5 Stormwater Management The site is underlain by glacial till. Infiltration is typically not feasible in the areas underlain by glacial till. We performed a small-scale pilot infiltration test in TP-i at a depth of 4 feet below grade. Following testing and application of correction factors for site variability(0.33), testing (0.4), and influent control (0.9), the infiltration rate was determined to be 0.21 inches per hour. This rate is lower than what is considered to be feasible for widespread infiltration. The near surface weathered glacial till is suitable to support permeable pavements, if utilized. We recommend a minimum concrete pavement thickness of 5 inches and a minimum base rock(choker and reservoir) thickness of 8 inches. We should verify stability of the subgrade prior to rock placement. 6 PO Box 82243 Kenmore,WA 98028 „eobaltgeora)4mail..cosn 206-331-1097