Dynamic Shear Strength of Frozen Sandstone Using the Punch Shear Test

Impacting loads such as blasting generally induce shear failure of frozen rock mass during excavation of frozen rock layer in mining and other engineering activities in high-altitude and latitude regions. However, the dynamic shear properties of frozen rock are inadequately investigated, especially, the influence of freezing temperature and impact loading rate remain unclear. This study conducted a series of punch shear (PS) tests on frozen sandstone by changing freezing temperature and loading rate. The results show that: (1) the dynamic shear strength of sandstone samples increases with decreasing temperature at the same impact air pressure, and there is an obvious freezing-induced strengthening effect. (2) With increasing impact air pressure at the same temperature, the dynamic shear strength of low-temperature sandstone samples increases more than that of normal temperature sandstone samples, and there is obvious loading rate effect. (3) Distinct shear planes form in PS samples, and samples are punched into two parts: rock ring and rock plug. (4) Based on nuclear magnetic resonance experiments, it is concluded that there are three microstrengthening mechanisms of freezing action on the dynamic shear strength of rock: (a) low-temperature shrinkage effect of mineral particles, (b) strengthening effect of ice particles supporting filling, and (c) strengthening effect of unfrozen combined water film cementation. (5) With the strain rate being >10−1 s−1, the dynamic strength of rock and ice increase significantly with the increase of strain rate, which leads to the loading rate effect on the dynamic shear strength of frozen sandstone.