Abstract: In permafrost region, rock joint as a mechanical weakness has great influence on the safety and durability of engineering projects. Studying the mechanical properties of frozen rock is of great significance for engineering construction in permafrost regions. To investigate the shear mechanical performance of frozen rock joints, four sets of natural joint surfaces of tuff collected from G214 National Highway in Qinghai Province were selected for direct shear test after being frozen at given temperature. Results show that the peak strength of the frozen rock joint is proportional to normal stress, and is inversely proportional to opening degree and roughness. When the opening of joint surface is greater than the maximum fluctuation of joint, the joint surface is dominated by disconnection failure mode, and the peak shear strength is controlled by adhesive force between ice and contact surface; when the opening of joint surface is smaller than the maximum fluctuation, ice shearing failure is the dominant failure mode under small normal stress; while under large normal stress, shearing failure of ice and rock both exist, and the peak shear strength is determined by the shear strength of both ice and rock joint. Furthermore, the peak shear strength criteria for frozen rock joints with various failure modes were derived.

Key words: Dangka hydropower station, local scour, dynamic mesh, VOF, shear stress, sediment transport rate, depth and topography