Kinematic Stability of Tunnel Face in Non-uniform Soils

Abstract

In the paper, the kinematic analysis is carried out to evaluate the face stability of shallow tunnel in the framework of plasticity theory. In view of the non-uniformity of soil strength parameters, a discretization technique is introduced to generate possible failure mechanisms which respect the associative flow rule and requirement of the non-uniformity of soil strength parameters. As an earthquake situation is considered, a pseudo-dynamic method is adopted to portray the distribution of seismic acceleration. Some comparisons are made to the conventional analysis, including discretization-based pseudo-static analysis and log-spiral-based pseudo-static analysis, to prove the validity of the programming code and accuracy of the proposed method. The soil strength parameters are considered varying in the vertical direction. The effect of distribution of strength parameters is discussed, and distribution form is initially assumed to be linear profile and, then, to be other nonlinear functional profile, including power profile, constant profile and quadratic profile. The results derived from further parametric study show that although the influence of horizontal seismic coefficient is more significant than the vertical one, the vertical effect cannot be ignored in most circumstances, and some factors affect the stability cyclically. In addition, in the linear profile of soil strength parameters, the influence of gradient on supporting pressure is rather small comparing to the average. The influence of non-uniformity of soil strength parameters and seismic parameters on the shape and collapsed area of the failure mechanism is successively studied in this paper. All the optimized solutions are presented in the figures and tables for practical application.