Abstract:

At present, there is a wrong understanding of the deformation of the initial support of the soft rock tunnel, which results in the waste of construction cost, the increase of safety risk, and the adverse effect of the progress being seriously restricted. Therefore, it is very necessary to study, analyze and control the deformation of the initial support of the tunnel. In this paper, the engineering practice of "mining method" proves that the reserved deformation of soft rock tunnel does not need to be set. Then, through various authoritative documents, it is explained that the concept of realizing the self bearing of surrounding rock with allowable deformation is a misinterpretation of " New Austrian Tunneling Method", which is wrong. Therefore, it is necessary to find out the real cause of support deformation and control it. Based on the analysis of six common displacements and their combinations of tunnel support, it is concluded that two problems need to be solved, i. e. the bearing capacity of the foundation and the strength of the support structure, in order to control the deformation of the initial support. Therefore, a structural mechanical model of chain link bearing with normal and tangential forces is established by" distributed anchor + steel frame + shotcrete and systematic distributed anchor simulation", which can calculate the stress of the support structure foot and the maximum stress of the support structure section, so as to obtain a clear standard for the bearing capacity of the ground base and the strength of the support structure, or provide a basis for improving the resistance of the support foot. Numerical basis. The results show that the systematic distribution of bolts can greatly reduce the bending moment, the axial force and the foot stress of the supporting structure, so as to enhance the bearing capacity of the supporting structure and reduce the stress of the base, and effectively control the deformation and settlement.

Key words: soft rock tunnel, initial support, mining method, NATM, support settlement, supporting deformation, two hinged arch, distributed anchor rod, steel pipe pile foundation