This paper discusses the results of a numerical study which examines the influence of the choice of joint constitutive model on the stability of jointed masses. The modeling methods and procedures presented here demonstrate a new approach to the simulation of a rock mass and the stability analysis of excavations. With this new approach, study of the stability of excavations can be carried out in such a way that the development and movement of the rock mass and failure process can be visualized. With the understanding of where the failure will start, how it develops and what the final failure can be studied and appropriate measures can be taken. In order to further study the damage mechanism of jointed and fractured rock mass, Burgers Model of joint rock model has been built by discrete element program (Particle Flow Code) to carry out numerical simulation. It adopts particle contact constitutive relationship, changes the properties of particle unit in calculation model and proposes macroscopic properties of samples in different parameters of particle unit to simulate damage process of granite sample with hole. The comparison of stress-strain curves obtained by the two-dimensional code of the Particle Flow Code (PFC) and by the test results has been made to further verify Burgers Model feasibility in the field of rock damage, and has certain application value to perfect rock constitutive relationship. At the same time, Particle contact constitutive relationship has been adopted to build the model of joint rock sample to carry out numerical simulation. It can describe non-linear behavior and localization with accuracy that cannot be matched by typical finite element programs. The consistency of stress-strain curves obtained by PFC2D and by the test results shows that PFC2D is a practical tool to produce AE events of jointed rock mass, and the Burgers Model is feasible in the field of rock failure, which provides an analysis of the microcracking activity inside the rock volume to predict jointed rock fracture patterns. The modeling of rock opening stability and failure reveals that the failure scale and failure mode of a tunnel of heavily joint rock are dominated by the joint quantity and quality in addition to the intact rock properties. The examples demonstrate the representational capability of the PFC code, this assessment will have very general application in jointed rock mass.
With the development of national economic and defense construction, people gradually recognize that the uses of underground space play an important role in the improvement of ground environment, such as subway, tunnels and underground caverns. Take the collapse of Hangzhou Metro in China (Zhou, et al 2009), for example, the safety of the excavation disturbed or damaged zone (EDZ) around underground rock attracts more attentions. The study of damage formation in jointed or bulk rock under stress has been a subject of widespread interest, the results of which have led to a number of comprehensive texts (Chang, et al, 2004;Eberhardt, 1998,1999; Stephen, et al 1998; Golshani, et al 2007).
