Development of an elastoplastic constitutive model for expansive soil under drying-wetting and freezing-thawing cycles
摘要
The complex drying-wetting and freezing-thawing cycles in cold and arid regions are key factors leading to the deterioration of expansive soil canal slopes and ultimately triggering slope failures. To investigate the failure mechanism of expansive soil canal slopes, triaxial tests, fissure characteristics tests, and microstructural analyses were conducted on expansive soil under drying-wetting and freezing-thawing cycles, with deterioration mechanisms analyzed from macro-, meso-, and micro-scale perspectives. The experimental results demonstrated that the stress-strain curves of the expansive soil exhibited strain-hardening behavior, while the volumetric strain curves showed compressive dilation characteristics. The cohesion decreased exponentially with the increasing number of cycles, with a reduction of 10.2% after the first cycle. It stabilized in the later stages of cycling, resulting in a total reduction of 26.2%. The internal friction angle remained largely unaffected by the cycling process. Longitudinal and inclined cracks developed in the expansive soil due to cyclic effects, eventually connecting to form a crack network that led to structural failure. At the micro-scale, as cycling progressed, some larger soil aggregates gradually separated into smaller particles, resulting in a total increase in the number of particles by 102.8%. In contrast, the total particle area, average particle size, area proportion, and average perimeter decreased by 27.9%, 46.9%, 31.6%, and 34%, respectively. Microscopic pores continuously connected and gradually formed new cracks. The relationship between cohesion and the crack connectivity parameter Q followed an exponential function, with cohesion decreasing as Q increased. Under cyclic conditions, microscopic pores continually evolved and interconnected, eventually forming meso-cracks. The formation of these pores reduced the interparticle forces, leading to a decrease in cohesion. Based on the modified Cam-clay model, an effective bonding stress parameter was introduced. The predicted curves showed good agreement with the experimental data, and the model parameters exhibited an exponential relationship with the number of cycles, with correlation coefficients R2 all exceeding 0.94, indicating strong reliability. The proposed model effectively captured the stress-strain and volumetric strain behaviors of expansive soil under cyclic conditions.