A dynamic constitutive model of unsaturated frozen soil with coupled frictional sliding and damage evolution of local cracks

The mechanical behavior and damage mechanisms of unsaturated frozen soil under impact loading were investigated based on impact compression experiments done at various temperatures (−5, −15, and − 25 °C) and strain rates (200–800 s−1) using a split Hopkinson pressure bar (SHPB). Our experimental results showed that the peak stress of unsaturated frozen soil increases linearly with strain rate, and strain–rate sensitivity and strain–hardening behavior are closely dependent on temperature. As the temperature decreases, both characteristics increase significantly. The nonlinear hardening and softening behavior of unsaturated frozen soil under impact loading can be attributed to the interaction between local crack frictional sliding and propagation. This study used a mixture theory to derive the relationship between microstructure and the elastic constants of unsaturated frozen soil. Drucker–Prager–type friction sliding criterion and damage criterion based on energy release rate were also employed to describe plastic deformation and damage evolution behavior when considering the strain–rate effects of cohesion and the degradation mechanism of local crack surface roughness caused by transient–temperature–rise–induced ice melting. Finally, a dynamic microscopic constitutive model of unsaturated frozen soil with coupled frictional sliding and damage evolution was developed. Its validity was verified by comparison with our experimental results.