Study On Shear Strength Of Frozen And Ice-containing Straight Rock Joint

With the global climate warming,the instability and failure of rock slopes in cold regions are becoming increasingly prominent.To investigate the shear mechanical properties and failure mechanisms of frozen fractured rock mass,a new type of THMC(Thermodynamics,Hydraulics,Mechanics,Chemistry)multi-field coupled shear test system was independently developed.The brittle shear failure characteristics of ice-rock interfaces under different normal stresses and ice layer thicknesses were systematically studied,and the microscopic mechanisms of rock shear fracture at different temperatures were investigated using numerical simulation methods.The main research contents and achievements are as follows:(1)The aperture of joints and normal stress have a significant impact on the shear strength of ice-filled joint.As the normal stress increases,the ability of ice-filled joint to resist shear significantly increases.During the process of increasing the thickness of the ice layer from 1mm to 5 mm,the peak shear strength and residual strength show a pattern of first increasing and then decreasing,and reach a peak at 2 and 3 mm.(2)During the shear failure process of ice-filled joint,normal stress and ice layer thickness affect the shear deformation characteristics.As the normal stress increases,the shear stiffness of ice-filled joint with the same aperture increases approximately linearly.The shear stiffness shows a trend of first increasing and then decreasing with increasing ice layer thickness,and reaches a maximum at ice layer thicknesses of 2 and 3 mm.Compared to sandstone,the shear stiffness of ice-filled joint in granite specimens is more significantly affected by joint aperture.(3)Freezing can significantly increase the cohesive strength of structural surfaces while greatly reducing their friction angle.As the thickness of the ice layer increases,the bonding effect of the ice layer on the joint increases,reaching a peak at a thickness of 2-3 mm,and showing a pattern of first increasing and then decreasing.The friction angle shows a non-linear deterioration trend with increasing ice layer thickness,and gradually stabilizes after the thickness approaches 5 mm.(4)Frozen rock is a system composed of ice layers and rock joints,and the failure of the system is mainly controlled by the cohesive and frictional forces between ice and joint surfaces,as well as the shear resistance of the ice layer,occurring at the weakest part of the system.The shear failure modes of ice-filled planar joints with different ice layer thicknesses mainly include four forms: wear slip of the ice film,shear failure of the ice layer,detachment failure of the icerock interface,and composite failure.The evolution of the mechanical behaviors,such as stressstrain characteristics and strength properties,are influenced by these forms.(5)As the normal stress increases,the shear failure ratio of ice-filled joint increases continuously,and the input energy,elastic strain energy,and dissipated energy at the failure point show a linear growth pattern.With the decrease of temperature,the total number of cracks in the jointed ice specimen increases significantly during failure.Compared to the-5℃condition,at temperatures of-10℃ to-20℃,the crack growth amplitude reaches 18.7% to74.1%.In addition,the required driving energy increases by 10.2% to 57.1%,indicating that the decrease in temperature enhances the resistance of joints containing ice to failure,and more driving energy is required for the specimen to undergo unstable failure.