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September 23,2022 <br /> Page 5 of io <br /> Geotechnical Evaluation <br /> Resistance to lateral footing displacement can be determined using an allowable friction factor of <br /> 0.4o acting between the base of foundations and the supporting subgrades. Lateral resistance for <br /> footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds <br /> per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12 <br /> inches below grade in exterior areas). The frictional and passive resistance of the soil may be <br /> combined without reduction in determining the total lateral resistance. <br /> Care should be taken to prevent wetting or drying of the bearing materials during construction. <br /> Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the <br /> footing excavations, should be removed prior to placing concrete. The potential for wetting or <br /> drying of the bearing materials can be reduced by pouring concrete as soon as possible after <br /> completing the footing excavation and evaluating the bearing surface by the geotechnical engineer <br /> or his representative. <br /> Concrete Retaining Walls <br /> The following table,titled Wall Design Criteria,presents the recommended soil related design <br /> parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall <br /> system is used. This has been included for new cast in place walls,if any are proposed. <br /> Wall Design Criteria <br /> "At-rest"Conditions(Lateral Earth Pressure—EFD+) 55 pcf(Equivalent Fluid Density) <br /> "Active"Conditions(Lateral Earth Pressure—EFD+) 35 pcf(Equivalent Fluid Density) <br /> Seismic Increase for "At-rest" Conditions 21H* (Uniform Distribution) 1 in 2,50o year <br /> (Lateral Earth Pressure) event <br /> Seismic Increase for "At-rest" Conditions 14H*(Uniform Distribution)1 in 50o year event <br /> (Lateral Earth Pressure) <br /> Seismic Increase for "Active" Conditions 7H*(Uniform Distribution) <br /> (Lateral Earth Pressure) <br /> Passive Earth Pressure on Low Side of Wall Neglect upper 2 feet,then 275 pcf EFD+ <br /> (Allowable,includes F.S.=1.5) <br /> Soil-Footing Coefficient of Sliding Friction(Allowable; 0.40 <br /> includes F.S.=1.5) <br /> "H is the height of the wall;Increase based on one in 50o year seismic event (so percent probability of being exceeded in <br /> 5o years), <br /> +EFD—Equivalent Fluid Density <br /> The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by <br /> water accumulation behind the retaining walls. Uniform horizontal lateral active and at-rest <br /> pressures on the retaining walls from vertical surcharges behind the wall may be calculated using <br /> active and at-rest lateral earth pressure coefficients of o.3 and o.5,respectively. A soil unit weight <br /> of 125 pcf may be used to calculate vertical earth surcharges. <br /> www.cobaltgeo.com (206)331-1097 <br />