Abstract: Affected by global warming, the subglacial debris on the Qinghai-Xizang Plateau in China is transforming from a frozen state into a thawing state, seriously affecting the glacier shear strength and glacier stability. In order to study the influence of thawing on the shear properties of subglacial debris, this paper introduced a new variable, the thawing rate, to quantitatively evaluate the amount of melted ice, and direct shear tests were carried out on thawing samples. Subsequently, a numerical model was established based on the finite-discrete element method to study the effects of thawing rate and gravel content on the shear behavior of subglacial debris. The results show that the thawing process significantly reduces the peak shear stress, cohesion, and inner friction angle. The relationship between shear strength parameters and thawing rate can be expressed using a linear relationship. The analysis of the factors affecting the shear strength parameters of thawing subglacial debris suggests that the reduction in the contribution of cementitious force can be responsible for strength degeneration. As the thawing rate increases from 2% to 4%, the deformation mode transitions from strain-softening to strain-hardening, and the failure mode shifts from rough serrated mode to smooth circular arc mode. Additionally, an increase in gravel content leads to a significant decrease in the shear strength of subglacial debris. However, the reduction range decreases as the thawing rate increases. This study provides valuable insights for evaluating the stability of glaciers by considering the effects of thawing on the shear properties of subglacial debris.

Key words: subglacial debris, thawing, direct shear test, shear behavior, finite-discrete element