Study on the deformation and failure modes of rock mass containing concentrated parallel joints with different spacing and number based on smooth joint model in PFC

Abstract

Engineering mechanical properties of rock mass are largely influenced by the characteristics of weak joints. Concentrated parallel joints are well developed in a large hydropower station in southwest China, and the deformation behavior of these joint belts is a key factor affecting slope stability. Therefore, this paper performed a simulation by particle flow code (PFC) and smooth joint model (SJM) to study the deformation and failure modes of rock mass containing concentrated parallel joints with different spacing and number. The following findings were obtained. (1) Four deformation phenomena of rock mass with concentrated joints were identified by field investigation: shearing along a single joint, shearing along multiple parallel joints, shearing across joints, and shearing through multiple joints and shaping as step-path deformation. (2) With the increase of joint number, peak strength and elastic modulus of rock mass decreased and the stair-shaped phenomenon of fracture became obvious. (3) The distance between tensile cracks, which are developed between joints during deformation process, has something to do with the joint spacing. Large spacing formed large distance, and small spacing formed small distance. (4) Although the elastic modulus decreased with the increase of smooth joint (SJ) number, no matter how big or small spacing is, for the rock mass with the same number of smooth joint, the elastic moduli are very close to each other. This may be the result of behavior of hard rock material and SJM assumption. The results of this paper illustrated that fracture developed along concentrated parallel joints should consider the interaction between joints. But how to consider and deal with the concentrated parallel joints for the slope stability calculation still needs more discussion.