STUDY ON SHEAR BEHAVIOR OF WAVY ROCK JOINTS FROM WAVELET ANALYSIS

In rock engineering,the shear behavior of jointed rocks mainly depends on the surface characteristics of joints. It has been found that rock joint surfaces can be decomposed into a first-order waviness and a second-order unevenness,which play different roles in the shear behavior. To quantitatively estimate their influences,we first used wavelet analysis to decompose granite joints and red sandstone joints,then counted the wavelength and undulation angle of the waviness and unevenness. A reasonable parameter research scheme was designed to investigate the shear characteristics of the two types of joints. Based on the 3D printing technology,rock-like samples were prepared,and laboratory direct shear tests and two-dimensional particle flow code(PFC^2D)numerical simulations were conducted. To reliably replicate the mechanical behavior of jointed rocks,the parallel bond contact model was used to mimic the rock sample. The smooth-joint contact model was used to reproduce the rock joints with undulation angles of 4°,8°,12°,16°,and 20°. The meso-failure mode and shear mechanical properties of jointed rocks during the shear process were analyzed. The influence of the undulation angle and normal stress was revealed. The specific results and conclusions are as follows.(1)The unevenness model is less likely to crack under low normal stress. Under high stress,for the waviness and unevenness models with a larger undulation angle,the cracks gradually propagate to the deep part of the sample. For the waviness model under low normal stress and unevenness model under high stress,the cracks are mainly parallel to the shear direction. For the waviness model under high normal stress,the cracks far from the undulation toe are almost perpendicular to the uphill slope,while the cracks near the toe are almost parallel to the shear direction.(2)The tensile cracks dominate,accompanied by a small amount of shear cracks,the amount of cracks increases with the increasing normal stress. Fewer cracks were identified under low normal stresses. In the case of high normal stress,the number of cracks increases sharply. In addition,the shear strength of the waviness is higher than that of the unevenness with the same undulation angle and under the same normal stress.(3)The undulation angle and normal stress are the key factors determining the shear strength,and the influence of wavelength is negligible. The predicted empirical formula for shear strength of joints was established,which considers the undulation angle θ, the normal stress σ_n, and the uniaxial compressive strength J C S: \tau=\sigma_\mathrmn \tan \lefta+b \ln \left(\fracJ C S\sigma_\mathrmn\right)+c\left(\theta \cdot \fracl_bl\right)+\phi_b\right . The model has been preliminarily verified through direct shear tests on jointed granite and red sandstone.(4)The relationship between the undulation angle and the friction angle of the waviness is y=0.7727x+12.88, and for the unevenness is y=0.706x+12.808.These findings provide theoretical support for predicting the strength of jointed rock masses,and are of significance for ensuring the safety and stability of rock engineering(e.g.,slope and tunnel).