A numerical study on mechanical behavior of jointed rock masses after tunnel excavation

Abstract

The tunnel in jointed rock masses is prone to be overbroken and then gives rise to collapse, yet the failure modes of jointed rock masses are still poorly understood. This paper investigates anisotropic deformations and failure modes of tunnels in jointed rock masses. For this purpose, five series of numerical models are modeled for a severe tunnel overbreak occurring on the Panlongshan tunnel. The ubiquitous joint model is used to consider the shearing and tensioning effects of the bedding and joint structures. The factors affecting anisotropic deformation and failure of rock masses, such as bedding spacing (s), joint dip angles (θ), and joint spacing (d), are discussed. The results demonstrate that for the stratified rock masses (without joint), the maximum settlement around the tunnel is located at the roof, and the separation of “virtual blocks” along the bedding planes is a basic failure mode; for stratified rock masses containing joints, the maximum deformation surrounding the tunnel appears in the joint position, and failure happens through a combined rotation, sliding, and falling mechanism. Our study can also reveal that with the increase of the number of joints, the plastic zone at the joint positions has a developing tendency towards the deep part. The more complex the joint structures in jointed rock masses are, the more unstable rock masses are formed.