Damage mechanism and dynamic constitutive model of frozen soil under uniaxial impact loading

Abstract

The dynamic mechanical properties of frozen soil at different temperatures and high strain rates were tested using a split Hopkinson pressure bar (SHPB), and the variation of the wave impedance of the frozen soil was analyzed. Viscoelastic theory confirmed that an increase in the wave impedance in frozen soil over short times is the result of unfrozen water relaxation. Unfrozen water is an important factor that increases the peak stress of frozen soil under impact loading. Based on the compression failure mechanism of frozen soil, the internal microcracks were classified as random or vertical microcracks. The mesoscopic parameter (microcrack density) and the macroscopic physical quantity (wave velocity) were connected by the effective medium theory, and the longitudinal wave velocity was selected as the damage variable. The effects of the low-frequency parameters in the ZWT (Zhu–Wang–Tang) model (Wang, 2003) when applied to frozen soil were evaluated. Under impact-loading conditions, with the initiation and expansion of the internal microcracks in the frozen soil, the Maxwell element represented by the low-frequency parameters lost its function rather than degenerating into a simple spring, and thus, it continued to contribute to the macroscopic mechanical properties of the frozen soil. Finally, damage was introduced into the improved ZWT model to establish a dynamic constitutive model of the frozen soil. The predicted and experimental results agreed well, which verified the applicability of the model.