Influence of confining pressure-dependent Young's modulus on the convergence of underground excavation

The actual convergence of an excavation located in fractured rock mass or the soft rock is largely different with the theoretical result in many cases. Experimental results showed that the influence of confining pressure on Young's modulus is very significant. This paper attempted to illustrate the influence of the confining pressure-dependent Young's modulus in the ground reaction analyses of mountain tunnel. Firstly, the relationship between Young's modulus and confining pressure was described as a non-linear function according to the test results. Based on the plane strain axial symmetry assumption and the incremental theory of plasticity, equilibrium equations and compatibility equations of rock mass around a circular tunnel were deduced theoretically. Based on fourth Runge-Kutta method, a semi-analytical solution was achieved. Considering the effect of confining pressure on Young's modulus, the stress and deformation of rock mass around tunnel was calculated by both analytical and numerical methods. The influence of confining pressure-dependent Young's modulus in surrounding rock was estimated quantitatively. Finally, Tawara saka Tunnel in Japan was taken as an example to explain the influence of confining pressure-dependent Young's modulus. The results showed that the error with respect to the monitoring data was largely reduced with the confining pressure-dependent Young's modulus model, which indicated the necessity of considering the non-uniform distribution of Young's modulus.