Effect of Overconsolidation on Cyclic Resistance of Soils

The effect of overconsolidation on the cyclic resistance ratio (CRR) for both non-plastic and plastic soils is examined using a laboratory test database, including cyclic triaxial, cyclic torsional, and cyclic direct simple shear (DSS) tests compiled from the literature. Based on the plasticity index ($PI$) and the ratio between water content during testing and liquid limit ($w_o/LL$), soils were divided into three series to interpret the relationship between CRR and overconsolidation ratio (OCR) using the stress history and normalized soil engineering properties (SHANSEP) approach. The resulting SHANSEP exponent $m$ was examined relative to key index parameters for each soil series. For non-plastic soils (Series I) in the DSS mode of shear, $m\approx 0.55$ for $CR{R}_{M=7.5}$ and is relatively independent of selected key index properties. This value is consistent with the typical value of $m=0.52$ defined elsewhere to describe the increase in undrained critical state shear strength ratio in monotonic loading with OCR for non-plastic soils subject to a similar consolidation profile. For low- to moderate-plasticity soils susceptible or moderately susceptible to liquefaction (Series II), $w_o/LL$ and liquidity index ($LI$) appear to roughly capture the trend of $m$ for $CR{R}_{M=7.5}$. For a limited number of higher-plasticity soils that are susceptible to cyclic softening (Series III), the range of $m$ for $CR{R}_{M=7.5}$ is relatively broad. Furthermore, the limited data suggested that Series III soils that are undisturbed (intact) or have low $w_o/LL$ and $LI$ may exhibit $m$ values that are significantly less than those measured for other reconstituted specimens over the same range of OCR.