Laboratory investigation of the pre- and post-cyclic volume change properties of Sherman Island peat

We investigate through laboratory testing the volume change characteristics of peaty organic soil from Sherman Island, California under static conditions (consolidation, secondary compression) and post-cyclic conditions. Incremental consolidation tests indicate the material to be highly compressible (Cc = 3.9, Cr = 0.4) and prone to substantial ageing from secondary compression (Ca/Cc = 0.05 following virgin compression). Strain-controlled cyclic triaxial testing of the peat finds the generation of cyclic pore pressures for cyclic shear strain levels beyond approximately 0.5-1.0%, with the largest residual pore pressure ratios rur (cyclic residual pore pressure normalized by pre-cyclic consolidation stress) being approximately 0.2-0.4. Post cyclic volume change occurs from pore pressure dissipation and secondary compression. The level of post-cyclic secondary compression increases with rur. Many of these phenomena have not been documented previously and suggest the potential for seismic freeboard loss in levees due to mechanisms other than shear failure