Abstract: Rock masses in cold regions are consistently subjected to a complex thermal-hydraulic-mechanical (THM) environment. The engineering behavior of these rock masses and associated geological disasters are closely linked to the coupled THM effects. A THM coupling creep test on freeze-thaw sandstone was conducted for rock slopes in open-pit mines in cold regions, simulating the complex freeze-thaw environment that the rock mass experiences. This study examined the time-dependent deformation and failure characteristics of freeze-thaw rock masses under THM coupling. The results indicate that: 1) Under the influence of THM coupling, a low-frequency periodic stress occurs in the sandstone, varying with the temperature cycle. This stress is the primary cause of creep damage accumulation and fatigue failure in the sandstone. 2) The creep process of freeze-thaw sandstone can be categorized into four stages: freezing stage, steady-state creep during freezing, thawing shrinkage stage, and steady-state creep post-thawing. During the freezing expansion stage, deformation primarily involves expansion strain, whereas in the thawing shrinkage stage, it predominantly involves compression strain. 3) An interaction exists between the freeze-thaw and seepage environments during the creep process of sandstone. Seepage replenishes water in the sandstone after thawing, intensifying freeze-thaw damage. Conversely, freeze-thaw conditions increase the porosity and pore connectivity of the rock, thereby enhancing the influence of seepage on the creep rupture of sandstone. This interaction creates a vicious cycle, exacerbating the creep failure of the sandstone. 4) During the creep process of freeze-thaw sandstone under THM coupling, a strong correlation exists between strain and seepage. The permeability of sandstone increases with cold shrinkage strain during the freezing process, while the phase change of pore water induces freeze swelling strain, subsequently reducing permeability. During thawing, permeability rises with thaw shrinkage strain due to the melting of pore ice. The permeability shows a gradually decreasing trend with the compression strain. This study reveals the creep and seepage characteristics of rock masses in cold regions under low-temperature THM coupling, providing a crucial scientific basis for the stability evaluation and disaster prevention and control of rock mass engineering in these areas.

Key words: sandstone, THM coupling, freeze-thaw cycles, creep characteristics, seepage