Abstract: In order to solve the failure of support structure of tunnel in high stress soft rock, based on the principle of reasonably releasing the stress in surrounding rocks and reducing the stress of support structure, a hydraulic tunnel graded yielding support structure is proposed. Considering the spatial effect of the excavation surface and the strain softening condition of the surrounding rocks, by analyzing the attenuation law of the virtual supporting force, the static balance equation of stress in the surrounding rocks, the virtual support force and the support reaction force is established. The synergy between the supporting structure and the surrounding rocks at each stage is studied to generate the relationship between the displacement and stress of the surrounding rocks in the whole deformation process of the support structure. The supporting effect of the proposed graded yielding support structure is revealed. The results show that the stress of surrounding rocks is significantly released at the two yielding stages and the deformation characteristics of surrounding rocks are consistent with the yielding characteristics of structure. The simulation results show the consistent variation trend with that of the theoretical values, which verifies the rationality of the theoretical analysis. The proposed yielding support structure can effectively release the stress in the surrounding rocks and reduce the stress of the supporting structure. It can avoid the yield failure of the support structure, solving the support problem of the tunnel in the soft rock with high stress, which can provide theoretical support for the application and development of the support structure.

Key words: tunnel engineering, stress relief, whole process analysis, virtual support force, strain softening