Research On Prestressed Anchor Cable Support Technique For The Tunnel With Large Deformation

With the traffic construction having the higher requirement of road line features and the quantity of the long tunnel has the continuous increasing; the effective support for the tunnel with large deformation is one of the issues which underground engineering must face. With the tunnel with large deformation, if the supporting method is normal bolt supporting, it will make the project cost rising, the bad supporting effect, and even bolt supporting system is failure. While, the prestressed anchor cable support is the active support method, because it has lots of advantages, such as high anchorage force, long anchorage length, and low dependence to surrounding rock. Therefore, it is urgent to seek the prestressed anchor cable support methods of the tunnel with large deformation, which can effectively control the displacement of the tunnel and ensure long-term security and stability of tunnel, which has important practical significance.Base on the related researches, the prestressed anchor cable support technique for the tunnel with large deformation is studied in this paper. The concrete research contents and main achievements are as follows:(1)Deeply analyze the deformation features of surrounding rock mass of the tunnel with large deformation, obtain the results as follows: The most important factors of forming the tunnel with large deformation are the expressing and expanding of the surrounding rock mass, and the expressing of the surrounding rock mass often leads the tunnel to form the large deformation; The most important features of the destroying of the surrounding rock mass of the tunnel with large deformation are the large radial deformation is formed after the excavation of tunnel, the steady period of tunnel is short when the supporting of the tunnel is finished just recently and the plastic region of the rock mass is large; The most important factors which affect the large deformation tunnel to form are geological structure, ground stress and mechanical properties of rock mass.(2)Deeply analyze the support mechanism of prestressed anchor cable, the result is prestressed anchor cable can effectively control the large deformation of the tunnel and improve the stress status of surrounding rock mass. Then basing on elastic-plastic theory of rock mechanics, put forward the calculation equations of the supporting parameters of prestressed anchor cable by considering the prestressing loss of the prestressed anchor cable, the non-uniform distribution of the shearing stress of anchorage segment of the cable and the influence caused by the internal friction angle of anchor agent to the anchorage effectiveness. Then proving these calculation- equation correctness by the calculation example.(3)By using the software FLAC^3D, the influences caused by changing the parameters of prestressed anchor cable such as interpretable spacing, diameter and prestressing force to the displacement of the tunnel with large deformation which depth is 750m,diameter is 6m,surrounding rock mass intensity degree is five are analyzed. Then determine the interpretable spacing and prestressing force are the parameters of the prestressed anchor cable which mainly control the displacement of the tunnel. Finally, optimize the parameters of prestressed anchor cable which mainly control the displacement of the tunnel with large deformation by orthogonally combine them. Then optimize the parameters of shotcrete, which are the strength grade and thickness, by orthogonally combine them. Finally, basing on the tunnel with large deformation, obtain the optimal prestressed anchor cable and shotcrete parameters. The optimal prestressed anchor cable parameters are interpretable spacing is 1.1m, the number of roots of teel strand which the diameter is 15.24mm and strength 1860MPa is four, the length is 20m, the prestressing force is 369kN. The the optimal shotcrete parameters are the strength grade is C25, the thickness is 25cm.