Effect of rock nonlinear mechanical behavior on plastic zone around deeply buried tunnel: An efficient semi-analytical solution

Adopting the novel proposed unified strain-hardening and strain-softening (UHS) model and finite difference method, an efficient semi-analytical solution is proposed to study the influence of the nonlinear behavior of rock on ground reaction. The proposed solution eliminates stress vibrations of the classical method that occurred in the strain-hardening zone, because it judges the elastic or plastic state of the calculation nodes before calculating the ground reaction; compared with the iterative solution, the proposed solution avoids iteratively solving for the plastic internal variables at each calculated node, resulting in that its computational efficiency is improved by more than 10 times. The proposed solution was verified by comparing it with the iterative solution, and numerical solution. Moreover, the effects of initial yield strength, peak strength, residual strength, and supporting pressure on ground reaction after tunnel excavation are studied. The results show that increasing the initial yield strength and residual strength will obviously decrease the plastic zone (PZ) and sub-zones. The peak strength of rock has limited influence on the radius of PZ, which mainly adjusts the ratio of each sub-zone in PZ. In addition, increasing the support pressure is an effective means to control the radius of PZ and sub-zones in deep buried tunnels.