Design Strengths for an Offshore Clay

Stability analyses for stage construction of a breakwater located offshore New Jersey required a detailed evaluation of the undrained stress‐strain‐strength properties of a plastic marine clay. One set of analyses, representing “conventional” practice, used UU triaxial compression tests to obtain the initial undrained strength $\left(c_u\right)$ and CIU triaxial compression tests to predict strength increases with consolidation. The second approach employed the Stress History And Normalized Soil Engineering Properties (SHANSEP) design procedure. This involved extensive consolidation testing to measure the in‐situ preconsolidation pressure and a comprehensive program of ${\mathrm{CK}}_{o}U$ tests sheared in compression, extension and direct simple shear modes of failure at varying overconsolidation ratios. A strain compatibility technique was applied to the SHANSEP data to account for the effects of anisotropy and progressive failure in circular arc‐ and wedge‐type stability analyses. The SHANSEP approach yielded design strengths significantly smaller than conventional practice. In terms of both the initial $c_u$ profile and the rate‐of‐strength gain with consolidation.