Study On Stability Of Tunnel In Jointed Fractured Rock Mass And Effect Of Bolt Support

In the progress of the rock initial formation and millions of years of evolution, the rock mass has undergone various complex geological process. So there are plenty of faults, joints and cracks other structural surfaces in rock mass. These types of structural surfaces are the weak part of the rock mass. Their stiffness and strength are much smaller than the rock matrix material. In the jointed fractured rock mass, the instability of tunnel is always because the blocks slip along the joint surface. In the past, most of the researches are based on continuous mechanics which idealize the jointed fractured rock mass as simplified continuous media. And simulate the joint surface by weaken the parameters of the rock mass. Although this approach has some Scientifics, but it ignores the differences between the joint surface and the rock mass, so it has some contrasts with the engineering practice.The paper simulates the tunnel build in jointed fractured rock mass by using the Universal Distinct Element Code program, and combining with the orthogonal design, separately analysis the tunnel environmental factors, the parameters of the rock, and the parameters of the joint affect on the stability of the tunnel. Then study the control of the tunnel stability of the bolt combined with the project of Lanzhou-Chongqing Passenger Dedicated Line to evaluate the effect of anchorage in jointed fractured rock mass by investigating the disturbed zone, the displacement around the tunnel, and the force of the bolt. At the same time introduce a bar element which considered the transverse shear effect. Compared the two bar elements to see the improvement of the tunnel stability after considering the transverse shear effect of the bolt. The main conclusions of this study are as follow:(1) The burial depth and the joint space are the main reasons of tunnel stability in the tunnel environmental factors. The shear zone expanded significantly with the increasing of burial depth and reducing of joint space;(2) The parameters of the joint surface is the main factors of tunnel stability. The slip between joints is mostly because the deformation and shear failure of the joint. For the layered rock mass, the slip between joints due to the deformation of the joint, so the parameters normal stiffness and shear stiffness of the joint are the main factors for the tunnel stability. For the block and fragmentation-like rock mass, the slip between joints due to the shear failure of the joint, so the parameters angle of internal friction and cohesion of the joint are the main factors for the tunnel stability;(3) In the layered rock mass, the bolt can increase the stiffness of the joint, thus the slip of the joint because joint deformation is cut down, so that the tunnel stability is enhanced. In the block and fragmentation-like rock mass, the bolt can increase the shear strength of the joint, thus the slip of the joint because joint shear failure is cut down, so that the tunnel stability is enhanced. The bar element which considered the transverse shear effect has significantly improvement on tunnel stability.