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• <br />• <br />• <br />DATE: March 12, 2003 <br />FROM: Allen Sorenson <br />RE: Suggested Conservative Soil Shear Strength Parameters for Stability Analyses <br />The following parameters are acceptable for gravel pits to be developed over weathered shale or <br />claystone bedrock, typical for front range pits, where site specific shear strength testing has not been <br />conducted. Given that these strength values, in particular the residual strength value for the <br />weathered bedrock, represent the worst -case for potential slope instability, any safety factor in <br />excess of one should be protective of critical structures. <br />CLAY, sandy, soft to stiff, very moist to wet, brown (CL): <br />o' = 28 degrees c' = 50 psf moist unit weight = 114 pcf saturated unit weight = 126 pcf <br />SAND, fine grained, clayey, silty, very loose, very moist to wet, brown (SC, SM): <br />(d' = 25 degrees c' = 10 psf moist unit weight = 90 pcf saturated unit weight = 115 pcf <br />SAND, fine grained, clean to slightly silty, dense, wet, brown (SP, SP -SM): <br />o' = 31 degrees c' = 0 psf moist unit weight = 117 pcf saturated unit weight = 130 pcf <br />SAND & GRAVEL, fine to coarse grained, some cobbles, clean to slightly silty, very dense, wet <br />brown (SP, GP): <br />o' = 35 degrees c' = 0 psf moist unit weight = 130 pcf saturated unit weight = 137 pcf <br />WEATHERED SHALE, this is an over - consolidated stiff - fissured clay, so the residual strength <br />values are appropriate to the analysis: <br />o' = 14 degrees c' = 0 psf moist unit weight = 125 pcf saturated unit weight = 142 pcf <br />c: \acs\My Documents\shear strength parameters.doc <br />l l <br />`PI NOV 3 0 REC'0 <br />