Three-Dimensional Face Stability Analysis of Deep and Shallow Tunnels in Rock Masses

Face stability is a critical issue in the stability analysis of tunnels, especially in soft soils and crushed rock masses. In this paper, considering two three-dimensional collapse mechanisms, upper-bound solutions are presented for determining the face pressure of deep and shallow tunnels excavated in rock masses. The Hoek-Brown failure criterion was considered for the rock mass surrounding the tunnel. The proposed upper-bound formulations were compared with three-dimensional finite-element simulations and also with centrifuge test results available in the literature. The obtained results showed that the face pressure decreases with increasing sigma(ci), m(i), and geological strength index. Besides, increasing the tunnel diameter and the rock mass density led to an increase in the face pressure, where for larger tunnels, the effect of the density became more pronounced. Finally, some charts were presented to specify the range of applicability of the concepts of deep and shallow tunnels. The results obtained from these charts demonstrated that the reduction in the Hoek-Brown parameters of the rock mass results in spreading the collapse mechanism from the tunnel face to the ground surface.

Automated summary

This paper discusses the issue of face stability in tunnel stability analysis, focusing on deep and shallow tunnels excavated in rock masses. The author presents upper-bound solutions for determining face pressure, taking into consideration different collapse mechanisms and the Hoek-Brown failure criterion. Results show that face pressure decreases with increasing certain rock mass parameters, and charts are provided to specify the range of applicability for deep and shallow tunnels. Additionally, it is demonstrated that reducing the Hoek-Brown parameters of the rock mass can lead to the spreading of collapse mechanisms from the tunnel face to the ground surface.