Effect of Cyclic Freezing and Thawing on Permeability and Mechanical Properties of Red Sandstone Under Triaxial Compression Condition

ABSTRACT: During the construction of coal mines in western China, many boreholes are drilled through artificially frozen Cretaceous and Jurassic formations. After experiencing one freeze-thaw cycle, these water-rich and weakly cemented rocks generally demonstrate significant changes in permeability and mechanical properties, leading to frequent occurrences of water intrusion and flooding accidents. In this study, triaxial compression test and permeability test were conducted on red sandstone under conditions of both no freeze-thaw cycle and one freeze-thaw cycle. The variation of permeability and mechanical characteristics of red sandstone induced by one freeze-thaw cycle was investigated for different confining pressures. The results indicated that, after one freeze-thaw cycle, the peak strength and elastic modulus of the red sandstone decreased but the Poisson's ratio increased. Under low confining pressures (4 and 6 MPa), the permeability of red sandstone exhibited staging characteristics. Enhanced by the freezing-thawing cycle, the permeability of red sandstone significantly increased before the onset of crack initiation. Under high confining pressures (8 and 10 MPa), the permeability showed a continuous decreasing trend, as the expansion of vertical fractures was suppressed by the high confining pressure. The test results from this work are helpful to stability analysis of the mine shaft and pre-control of seepage damage after the thawing treatment of the frozen coal mines. 1. INTRODUCTION During the construction of coal mines using artificial freezing method in western China, the frozen boreholes often pass through the Cretaceous and Jurassic formations. These water-rich and weakly cemented rocks are characterized as late diagenesis, poor cementation, low strength, and easy to become mud when encountering water (Zheng et al., 2011; Ma et al. 2018; Weng et al.2021). After experiencing artificial freezing and natural melting process, the permeability and mechanical properties of the rock further weaken, leading to frequent occurrences of water intrusion and flooding accidents (Deng et al. 2010; Huang et al. 2022; Xiong et al. 2023). Ultimately, it can cause significant losses of economy and threaten the safety of lives and property of humans.