600 54TH ST SW I Geotech Report 2025-01-29

GEOTECHNICAL INVESTIGATION EVERETT,WASHINGTON March 2,2018 A i/3 increase in the above value maybe 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 18 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 1 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 275 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. A 1/3 increase in the above values may be used for short duration transient loads. 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 weathered and unweathered glacial till which is nearly impermeable and not conducive to infiltration of stormwater runoff. We planned on conducting at least one in situ infiltration test to determine infiltration feasibility. However,groundwater was encountered at shallow depths which preclude the suitability of the site for infiltration BMPs. There is inadequate clearance below any system and the observed groundwater. Furthermore,the site is underlain by glacial till,which is nearly impermeable in its unweathered state. We anticipate that runoff will be managed through the use of a detention vault system with overflow to City infrastructure. We can provide additional recommendations for detention vaults,ponds,or other stormwater infrastructure upon request. We should be provided with the final plans to verify suitability of any system from a geotechnical standpoint. 9