Frost heave failure of water-bearing fractured rock mass under the combined effect of freeze-thaw-compression-shear load

The instability of rock slopes in cold regions is closely linked to the development of dominant fractures，with the freeze-thaw environment and load conditions serving as direct triggers for the expansion of these fractures. Therefore，understanding the frost heave characteristics of water-bearing fractured rock masses under the combined effects of freeze-thaw and load is a crucial prerequisite for preventing and controlling slope disasters. Using a self-developed loading device，the freeze-thaw tests on fractured rock mass under compressive and shear forces were conducted to identify patterns in the temperature field，stress field，frost heave force，and end strain during the freeze-thaw process. The numerical model was established to simulate the freeze-thaw process in fractured rock masses under compressive-shear loads，systematically analyzing the frost heave expansion law of rock mass fractures under the coupled action of freeze-thaw and various combinations of compressive and shear loads. Finally，the three-dimensional schematic diagram illustrating the zoning of fracture rock mass failure types was summarized，and the key indicators such as loaded freeze-thaw failure surface and compression shear promotion zone were proposed. The results show that，the variation of temperature and frost heave force during a single freeze-thaw cycle exhibits similar characteristics，which can be divided into seven stages. In repeated freeze-thaw cycles，the peak frost heave force decreases with an increasing number of cycles，but it decreases rapidly in the early stages of the cycles，remains stable in the middle stage，and dissipates due to damage in the later stage. With the increase in the number of freeze-thaw cycles，the strain value at the crack tip of the rock mass under compression and compression-shear action gradually increases. Compression and shear loads exert inhibitory and promotive effects on the frost heave deformation of fractured rock，respectively. The application of shear load accelerates crack development，with a higher load resulting in faster crack propagation. After the application of compressive load，crack development accelerates in the early stages of freeze-thaw cycles but gradually slows down in the middle and later stages. However，the number of freeze-thaw cycles required for ultimate failure increases. The shear load in compression-shear load combination is the dominant load. The properties of the rock mass，freeze-thaw environmental conditions，and load magnitude not only affect the freeze-thaw failure law of loaded fractured rock masses but also alter their failure mechanisms.