Experimental investigation and modeling of the mechanical behaviour of Yanji swelling mudstone subjected to wetting-drying-freezing-thawing cycles

Abstract

Rocks and soils in seasonally frozen regions are subjected to cyclic wetting–drying-freezing-thawing (WDFT) process. The influence mechanism of WDFT process on their mechanical behaviour is not fully understood and the existing constitutive models are not capable of capturing the strain-softening behaviour under WDFT cycles. In the present study, a series of consolidated drained triaxial compression and mercury intrusion porosimetry tests were performed on Yanji mudstone subjected to WDFT cycles. Results indicated that the WDFT cycles could induce a large amount of cracks and large pores between aggregates and compress the aggregates with a decrease of the intra-aggregate pores. After cyclic WDFT process, the specimens exhibited more significant strain-softening and dilative behaviour. The elastic modulus, peak and residual shear strengths of the mudstone decreased significantly with increasing WDFT cycles, especially in the case of low confining pressures. These decreases were more pronounced in the first four cycles and became negligible after 4 cycles. As the cyclic number increased, the cohesion of specimens decreased remarkably owing to the presence of cracks and the destruction of bonds between aggregates. By contrast, the effective friction angle, Poisson’s ratio and dilatancy angle increased with the WDFT cycles due to the more compact aggregates induced by the high suction during drying process. A nonlinear elastic constitutive model was developed for describing the strain-softening behaviour of Yanji mudstone subjected to WDFT cycles. The deviator stress-axial strain relationship predicted by the proposed model agreed well with the measured one, indicating the relevance of the predictive model.