Study On The Action Mechanism And Supporting Effect Of Yielding Bolt In Deep Buried Soft Rock Tunnel

Coal mine roadway, diversion tunnel and other large buried underground caverns often go through the weak rock. As the most commonly used technical means used in geotechnical and mine engineering, Bolt support can effectively improve the soft rock stability.The deformation of the traditional bolt is small and can not adapt to the large deformation of the soft rock around the tunnel, however the emergence of the yielding bolt effectively solves this problem.Based on the previously developed yielding bolt, this paper uses FLAC3D to simulate the pull-out test of both the yielding bolt and the ordinary. The study shows that when the bolt is pulled, The axial force of the bolt is the largest at the end of the anchor, and gradually decreases along the shaft, and the amplitude of the yielding bolt is larger than that of the ordinary ones. With the increase of drawing force, the axial force of the bolt increases, and the increasing speed of the axial force of the yielding bolt is fast than ordinary ones. The study shows that the FLAC3D simulation of the pull-out test matchs the indoor and field tests by comparing previous studies and proves the feasibility of simulating the shear resistance of the anchor.The supporting effect of the common bolt and the bolt in the soft rock tunnel is compared and analyzed. Compared with the common bolt,the speed to reach the yield strength of the yielding bolt is slower and will maintain a longer time. The largest bearing capacity of middle of common bolt is easy to be pulled off,and the axial force distributs like an"hourglass". The yielding bolt can be maintained for a long time after the yield strength, and the axial force distributs like an "spindle". The elastic distance of 6 m theyielding bolt is 70.54 mm and the plastic pressure distance is 130.65 mm.Based on the engineering background of Qinling deep-buried soft rock tunnel in Hanjiang-to-Weihe river diversion project, in order to resolve the problem of TBM being stucked, FLAC3D is used to simulate the supporting of Qinling deep tunnel. Based on the field rock mechanics test, the parameters of the rock mass are estimated. According to the measured results, the parameters of the surrounding rock are determined by back analysis. It is found that the common bolt is prone to break failure, and the yielding boltr can adapt to the deformation of the surrounding rock because of the large extension of the pressure component. It will play a supporting role for a long time, so as to achieve the effect of controlling the deformation of the surrounding rock. In order to solve the problem of TBM stucking in the Qinling deep tunnel,The yielding bolts are supported in the broken section and the common bolts are supported in the normal section. The numerical simulation results of this scheme are basically consistent with the measured results.The subsequent engineering practice proved that the implementation of this program can effectively solve the problem of TBM stucking, and successfully out of the trouble.