Micro-Constitutive Relations Of Frozen Soil Under Impact Loadings

The essential characteristic between conventional melting soil and frozen soil is the existence of ice in frozen soil. The content of the unfrozen water and the ice in the frozen soil would change because they can transmute into each other constantly under different operating conditions, so the mechanical properties of frozen soil are complex. And researches in dynamic fields started later than researches in static fields, so it is difficult for frozen soil to build dynamic impacting constitutive models. Currently, researches about the dynamic impact constitutive relations of frozen soil mainly focus on macroscopic phenomenological aspects.In this research, the SHPB impact loading experiments with three high strain rates(700/s,900/s,1200/s) for four groups of frozen soil specimens composed of different particle size(rough, middle, tiny, mixed) under three frozen temperature(-5℃,-15℃,-25℃) were done.Under uniaxial dynamic impact, the stress-strain curves of frozen soil rapidly rise to the peak and then decrease slowly, which shows obvious brittleness characteristic. The curves experience four periods(elastic rising period, strain hardening period, strain softening period, destroying period).Frozen soil has the obvious strain rate effect:the peak stresses and final strains increase with increasing strain rate. Frozen soil has the obvious temperature effect:the peak stresses increase with decreasing freezing temperature. The peak stresses of frozen soil with different particle sizes at the same operating conditions are obvious disparities(in the order of largest to smallest:fine specimens, middle specimens, and rough specimens. The peak stresses of the mixed specimens reside between those of the fine and middle specimens). Strain convergence phenomenon only relates to strain rate.In this research, a dynamic impact micro-constitutive model for frozen soil based on ice particle reinforced aspect was proposed. The model regards frozen soil as the composite material composed of ice and soil. Then the strain rate item is brought in the dynamic elastic modulus of soil. Finally the dynamic impact micro-constitutive model containing strain rate item and temperature item adapt to engineering practice is obtained.In this research, a coupled damage-plasticity micro-constitutive model for frozen soil was proposed. Based on SHPB experimental results, adopting damage and failure principle of Druger-Prager, a dynamic micro-constitutive model with coupled damage-plasticity to describe mechanical behavior of frozen soil subjected to impact loading was proposed. Macroscopically, frozen soil is assumed to be homogeneous and consecutive, but a large amount of micro-cracks and micro-voids are distributed randomly throughout the frozen soil. When frozen soil specimen is shocked hard, The propagation of micro-cracks and the collapse of micro-voids can induce damage. Definition and evolution equation of the two damage were proposed.