A Semi-analytical Solution of Face Extrusion Deformation Considering Nonlivnear Changes of Rock Mass Mechanical Parameters

摘要

The stress state of rock mass is redistributed after the tunnel excavation, resulting in different confining stress at different radial distances. Relevant studies demonstrate that the mechanical characteristics of rock are related with the confining stress, causing various the mechanical parameters of rock mass at different radial distances. This paper aims to take these kinds of mechanical properties of rock mass into the analytical solutions of stress and deformation around the tunnel face. Firstly, the calculation formulas of the rock mass mechanical parameters changing with the confining stress is determined based on the existing rock triaxial test data. Then, a new model considering the influence of confining stress is proposed based on Mohr-Coulomb (M-C) failure critical. At the same time, an given radial length increment divides the plastic zone into a series of concentric annuli. The finite difference approach may be used to compute consecutive stress and strain increases for each annulus. A comparative analysis of the Pierpaolo Oreste's model and the proposed model is carried out through calculation examples, and the results show that: ignoring the effect of the confining stress on the mechanical parameters of rock mass, the plastic radius of the tunnel face will be smaller than the actual value, and the face extrusion deformation value will be larger. It is emphasized that the influence of confining stress on the mechanical parameters of rock mass should be considered in actual engineering calculations, especially the high initial stress rock mass. Finally, combined with the numerical calculation model, the rationality of the application of the circular tunnel elastoplastic model in the non-circular tunnel is verified.