Numerical Simulation Of Failure And Stability Analysis Of Rock Tunnels In Jointed Rock Masses Using Strength Reduction Method

There are all kinds of defects in rock masses which form a variety of weak discontinuity structure planes,such as joints,flows and faults etc..The different kinds of structure planes lead to inhomogeneity of engineering rock mass.The structural planes often play critical role resulting in instability and failure of the rock mass.After excavation in the jointed rock mass,stress release sometimes resulting in the destruction of the tunnel engineering.Due to the obvious randomness,discontinuity and multi-scale complex features of the jointed large distributed in the rock mass,the stability study of tunnels in jointed rock masses becomes even more complicated.Nowadays,the common way to study the stability study of tunnels in jointed rock masses is the combination of monitoring,physical experiment,and numerical simulation.In most studies,physical model test or numerical simulation research on the stability of joint rock tunnels,are usually conducted by the way of loading step by step until the damage state is achieved.This is not consistent with the cavity of the boundary conditions and the actual situation.In this paper,the method called Strength Reduction Method is applied to the study of stability of tunnel in jointed rock masses using a numerical code called RFPA(Realistic Failure Process Analysis).In the numerical simulation,the mechanical parameters of surrounding rock is gradually weakened and the in-situ stress is unchanged,and this is more consistent with the actual situation.The maximal damage number of the elements is used to be the failure criterion of the tunnel models.The content includes the following aspects:(1)The effect of cavity section shape on the stability of the tunnels.The results show that cavity section shape has a great influence on the stability of the tunnels.Usually the circular cavity stability is best,straight wall arch cavity stability is in the middle and square cavity stability is the worst.(2)The effect of joint angles on the stability of the tunnels.The results show that joint angle has a great influence on the stability of the tunnels.The models with a low dip angle or with a high dip angle go against the stability of tunnel,while a moderate joint dip angle is beneficial to the stability of tunnel.(3)The effect of lateral pressure coefficient on the stability of the tunnels.The results show that lateral pressure coefficient has a great influence on the stability of the tunnels.Within a certain range,the improvement of lateral pressure is helpful to the safety stability of the tunnel,beyond a certain range,the improvement of lateral pressure promotes the destruction of the cavity.(4)Using the confining loading method to simulate the gradual damage instability process of different cross section shape of cavity,and comparison with the result by strength reduction method.The results show that under different loading method,the safety rule of different cross section shape of cavity is the same,but the destruction process and destruction form are different.Under the confining load method,three kinds of cross section shape of the cavity all have a certain width of obvious damage zone and fissure zone.