Failure of Underwater Slope in San Francisco Bay

The failure of a 90-ft-high (27 m) underwater slope in San Francisco Bay is used to assess the accuracy of conventional laboratory and field vane shear tests for measuring the undrained strength of a normally consolidated clay. The net effect of systematic errors due to disturbance, anisotropy, cap and base restraint, and the use of triaxial rather than plane strain tests was apparently small in this case, but the reduction of undrained strength due to creep under continued loading was significant, and the effect of creep strength loss can explain the discrepancy between the strength measured in the laboratory and that modified at failure in the field. Empirical corrections for measured strength are recommended