Stability of Tunnel Roof in Nonhomogeneous Soils

Abstract

The stability of tunnel roof is investigated in nonhomogeneous soils using the theory of plasticity. Based on the nonlinear failure criterion, the expressions of tunnel roof in nonhomogeneous soils are deduced, and the influence of pore pressure is taken into account. The soils are nonhomogeneous in the vertical direction only. Due to the complexity of the differential expressions obtained, a multilayer method is proposed that divides the soil mass into finite layers. Numerical results for tunnel roof stability are obtained through iterated calculation. The results show that the height of the collapsing block increases with increases in the variation of cohesion with depth, while its length increases with increases in the cohesion of the soil mass at the tunnel roof. The rate of increase of cohesion with depth plays an important role in the stability of tunnel roof.