Numerical study on the mechanism of shear performance degradation of thawing glacial debris

The sensitivity of the ice-water transition in glacial debris to temperature rise has become a significant concern. In recent years, there has been an increase in reports of ice avalanches caused by the thawing of glacial debris, which can be attributed to the impact of global warming. To study the temperature-dependent degradation of shear strength in glacial debris, a Finite Discrete Element Model (F-DEM) was developed. This model consists of solid permafrost and gravel elements and cohesive elements, as well as cohesive elements. The strength degradation law of the glacial debris, as observed in tests, is described as a strength degradation process of the cohesive elements. Initially, cohesive elements using the “traction-separation” criterion are set in between solid elements to represent interstitial ice. Subsequently, a strength degradation law governing the degradation law is implemented through the development of the VUSDFLD subroutine in Abaqus. The strength degradation of the cohesive elements is controlled by temperature field variables. The macroscopic numerical results obtained from the simulation were compared to experimental results. The simulated shear characteristics, including peak shear strength, deformation mode, and failure mode closely matched the experimental findings. The influence of three different factors, namely the thawing rate, gravel content, and stress magnitude on shear behavior was investigated. When the thawing rate is less than or equal to 2%, the failure mode exhibits a rough “serrated” pattern; as the thawing rate increases (> 2%), the shear surface gradually transitions to a smoother “circular arc” shape. The significant difference in strength at the permafrost-gravel interface can easily lead to stress concentration, resulting in cracks propagating along the interface. Increasing gravel content leads to a decrease in the shear strength of glacial debris, and the sensitivity of the shear strength to gravel content decreases with increasing thawing ratio. Under high shear loading, even a slight increase in temperature can cause sudden changes in shear strain. The deformation under constant load can be divided into three stages: the initial stage, the developmental stage, and the rapid deformation stage. In the initial stage, shear strain initially increases and then stabilizes; and during the developmental stage, there is a critical point in strain; during the rapid deformation stage, shear strain increases rapidly. The temperature of the critical point decreases with an increase in initial shear stress, and they are approximately linearly related. At higher shear stress levels, the shear strain of glacial debris is highly sensitive to temperature changes. Further studies should be conducted on model simplification, variation laws of parameters, phase transitions, and size effects to better simulate the shear strength degradation behavior under actual glaciers.