Variations in dynamic shear modulus of loess exposed to dry-wet cycles from Xi'an area, China

Abstract

For undisturbed loess with water sensitivity and dynamic vulnerability, which is often in a state of damage accumulation due to the influence of natural factors (the fluctuation of groundwater level, rainfall infiltration/evaporation, and seismic load), the impact of relevant engineering problems is significant, and the disaster-causing process is complex. Cyclic simple tests were used to illustrate the behaviour of the dynamic shear modulus of loess exposed to various factors of dry-wet(D-W) cycles and stress conditions (D-W cycles times N, lower limit water content w1, and consolidation stress σv). Using scanning electron microscopy (SEM), we assessed the inherent damage mechanism under D-W cycles. The findings show that the D-W cycles considerably affect the dynamic shear modulus of undisturbed loess, with the strongest effect occurring during the first D-W cycles. Based on the Hardin hyperbolic model, the stress exponent n is a specific parameter of w1. In addition, the relationship between N and G0/Pa/(σv/Pa)n is a power function, and G0/Pa/(σv/Pa)n drops as w1 and N increase. The fitting parameters a of the dynamic shear modulus ratio normalization model are not sensitive to σv/Pa, D-W cycles times N, and lower limit water content w1. Based on the dynamic shear modulus, a damage degree prediction method considering N, w1, and σv is established. The results can provide a theoretical reference for earthquake disaster prediction in collapsible loess areas.