Study on dynamic shear deformation behaviors and test methodology of sawtooth-shaped rock joints under impact load

Shear slip of rock joints under dynamic disturbance is a major factor causing disasters such as landslides and cavern instability. To explore the dynamic shear deformation behaviors of rock joints, an impact-induced direct shear test applicable for jointed rock specimen is conducted. A biaxial Hopkinson pressure bar (BHPB) equipment is employed, which can simulate intensive disturbances encountered during engineering construction in rock masses. Tangential and normal dynamic stresses on rock joint can be measured simultaneously through stress wave acquisition. Dynamic displacements are obtained based on a two-dimensional digital image correlation (2D-DIC) technique. Firstly, the feasibility of the experimental method is verified by trial tests on metallic specimens. The measurement technique for obtaining the dynamic stress and displacement of joint is proposed. Then, a series of dynamic shear experiments are carried out on jointed and intact granite specimens, respectively. The dynamic shear deformation of the specimens is obtained, and the effects and mechanisms of undulating angle and initial normal stress on the dynamic shear deformation are discussed. The test results show that, due to the variable input force and normal stress, the shear rate varies. The dynamic slip of the joint can be divided into three sub-stages: slip initiation, secondary stress accumulation, and post-slip. The shearing process of intact rock includes two stages: shear stress accumulation and post-peak damage. Deformation rebounding is also observed in the jointed and intact granite specimens. The maximum shear displacement is negatively correlated with the normal stress and the undulating angle. Based on the distribution and evolution of displacement field in rock specimen, the effects of undulating angle and normal stress on the shear strength and the maximum shear displacement are revealed. Finally, the damage modes of rock joint under different conditions are discussed.