Bearing effect of prestressed bolt-anchored structures and mechanical analysis of surrounding rock

Because of complicated interaction mechanism between bolt and surrounding rock in tunnels, the design is mostly based on the analogy method and experience. Starting from the anchorage structure formed by the bolt in continuously uniform strata, a formula for bearing strength is established, and the parameters in the formula are determined. By analyzing the bearing characteristics of anchorage structure, the influence degree of different factors on the bearing strength can be obtained. On this basis, the definitions of "amplification factor of supporting force " and "strength of anchor circumscription" are put forward. Besides, the anchorage structure can be equivalent to the support stress so as to resolve the stress distribution of tunnel surrounding rock, plastic zone and displacement, which is verified by the numerical simulation and numerical example. The results show that anchorage structure has an amplification effect on bolting force and provides a strong supporting force in the surrounding rock of deep tunnel. The influence degree structure for the strength of anchorage is followed by mechanical parameters, anchoring thickness and supporting strength from large to small, among which the mechanical parameters play a crucial role in the bearing strength of anchorage, and the reasonable anchoring thickness is 0.4~0.8 times the diameter of the tunnel. Furthermore, the stability control principle of surrounding rock is proposed. By comparing the theoretical results with the bolt support and equal effectiveness support in the numerical simulation, the plastic zone, stress distribution and displacement around the tunnel are basically the same. The proposed theories may provide a scientific analysis method for the stability control of the tunnel with bolt support.