Calculation model of rock joint stiffness considering anisotropic morphology characteristics

To accurately and conveniently achieve the shear and normal stiffnesses of rock joint and analyze the deformation behavior characteristics of rock joint, the diorite joint from the Guanshan Tunnel was scanned to obtain the digital information of morphology. According to the digitized joint surface, the replicate joint samples were made by the 3D printing technology. The uniaxial compression tests and anisotropic shear tests were performed for the joint replicas. The new shear and normal stiffness models were established based on the new anisotropic morphology parameter. Research results show that the proposed new morphology parameter takes into account the climbing angles and heights of positive asperities, which is helpful for expressing the anisotropic roughness of joint surface. The morphology parameter of joint profile in the same direction follows a lognormal probability distribution. On the basis of mechanical tests on the physical models, the new shear stiffness calculation model of rock joint established by considering the morphology parameter, joint compressive strength, and normal stress can lower the difficulty in obtaining the shear stiffness, and better reflect the anisotropy of tangent deformation as well. In consideration of the quantitative relationships of joint compressive strength with the initial normal stiffness and joint maximum closure, the improved hyperbolic-function normal stiffness model can simplify the calculation of normal stiffness by avoiding complex mechanical experiments. Compared with the classical calculation models and the mechanical test results, the stiffnesses calculated by the new models are closer to the test values. The average relative error between the calculated and experimental values of shear stiffness is 2.09%-27.88%, and the average relative error between the calculated and experimental values of normal stiffness is 3.25%-17.25%, which demonstrates that the new models can obtain the deformation parameters of the joint more precisely and conveniently. © 2022, Editorial Department of Journal of Traffic and Transportation Engineering. All right reserved.