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 (C_c = 3.9, C_r = 0.4) and prone to substantial ageing from secondary compression (C_a/C_c = 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 r_ur (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 r_ur. 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.

When the direct shear test is performed in accordance with ASTM guidelines, the measured shear stresses at failure estimate drained strength parameters.  We investigate the possibility of estimating undrained strength using direct shear testing at variable shear displacement rates on specimens composed of various combinations of kaolinite and bentonite. Even at fast displacement rates, constant volume conditions are not achieved in the direct shear device because of changes in specimen height that are large relative to allowable ASTM thresholds for constant volume simple shear testing. However, undrained strengths established by constant volume simple shear testing at slow strain rates are well approximated by direct shear tests conducted at fast shear displacement rates (time to failure < t₅₀/8, where t₅₀=time to 50% consolidation in a conventional oedometer test). Because of the simplicity of direct shear testing, such estimates of undrained strength may be useful in engineering practice when access to a simple shear device is limited. Nevertheless, fast direct shear tests have shortcomings, including lack of control of rate effects, and constant volume testing is recommended for critical projects.

Remote data monitoring was performed to measure settlement and pore pressure in soft peat beneath a model levee constructed in the Sacramento / San Joaquin Delta. Consolidation and secondary compression behavior was monitored following construction and dynamic testing of the model levee using piezometers embedded in the peat and an in-place horizontal inclinometer at the base of the model levee. A solar powered data acquisition system was used to gather the data, and a modem transmitted the data to a web-based interface. This system enabled us to (i) know when primary consolidation had finished prior to testing, (ii) observe the large influence of secondary compression on observed settlements, and (iii) observe a lack of any significant post-cyclic settlement. The initial change in pore pressure was predicted well using Skempton's pore pressure parameters.