Characteristic Analysis of Crack Initiation and Crack Damage Stress of Sandstone and Mudstone under Low-Temperature Condition

Abstract

The artificial freezing technology is one of the most effective methods during the excavation on the water-rich strata in western China. This study on crack initiation and damage stresses of rock at low-temperature conditions has an important guiding role in understanding the failure process of frozen rocks. This paper investigated variations of the crack initiation and crack damage stresses of the sandstone and mudstone samples with decreasing temperature. The results showed that, for the sandstone sample, the crack initiation stress, crack damage stress, peak stress, crack initiation stress ratio (i.e., the ratio of crack initiation stress to peak stress), and crack damage stress ratio (i.e., the ratio of crack damage stress to peak stress) increased linearly with the decreased freezing temperature; for the mudstone sample, the peak stress increased linearly with the decrease of the freezing temperature, but the crack initiation stress, crack damage stress, crack initiation stress ratio, and crack damage stress ratio increased first with the decrease of the temperature then decreased with temperature once it was lower than −10°C. This was because the mudstone sample experienced more severe frost heave damage than sandstone during the freezing process, which caused significant inhomogeneity of the mudstone sample. For the sandstone, the crack initiation stress and crack damage stress increased linearly with the increase of peak stress. Based on the discovered relationships, the peak stress of the sandstone can be predetermined according to the crack initiation stress or crack damage stress of the sandstone. However, for the mudstone, the crack initiation stress and crack damage stress did not show an obvious trend of change with the increase of peak stress. These experimental results were useful for understanding the failure process of frozen rocks in cold regions and artificial freezing engineering.