Effect of Initial Consolidation Condition on Postcyclic Undrained Monotonic Shear Behavior of Mississippi River Valley Silt

The postcyclic undrained monotonic shear behavior of Mississippi River Valley (MRV) silt is investigated by carrying out triaxial tests under various initial consolidation conditions. Results show that the variation of cyclic shear strength of MRV silt against initial overconsolidation ratio (OCR) and mean effective consolidation pressure (${\sigma }_c^{\prime }$) was consistent with previous studies, i.e., it increased with both increase in OCR and decrease in ${\sigma }_c^{\prime }$. The cyclic stress ratio (CSR) had no apparent effect on postcyclic shear behavior for MRV silt. At higher OCRs, the postcyclic reconsolidation behavior was more similar to recompression. Unlike the specimens not previously subjected to cyclic loading, the initial OCR did not influence effective stress path of the postcyclic reconsolidated specimens at the early stages of shearing. The normalized undrained shear strength ($S_{u,OC}/S_{u,NC}$) of MRV silt reconsolidated after cyclic loading increased with OCR. Stress-strain curves of MRV silt reconsolidated after cyclic loading can be normalized by ${\sigma }_c^{\prime }$ as those of the specimens not previously subjected to cyclic loading. Without reconsolidation, the liquefied specimens tend to dilate at the early stage of postcyclic undrained monotonic shearing phase. The undrained shear strength of the specimens not reconsolidated after cyclic loading did not approach to zero, and it increased with an increase in OCR. The undrained shear strength of postcyclic MRV silt can be predicted based on the equation $S_u=M/2\times p_0^{\prime }\times {10}^{-\psi /\lambda }$. However, cyclic loading changes the critical state line (CSL) of MRV silt, and the prediction will be better if the state parameter is computed based on the postcyclic CSL.