Analysis of working face stability of longitudinally inclined shield driven tunnels in frictional soils

Abstract

The shield machine has the advantage of reaching the predetermined depth more quickly with an inclination angle α, compared to conventional horizontal excavation. This paper aims to investigate the working face stability of shield tunnel driven with an inclination angle. An improved model is proposed by incorporating α into the traditional silo-wedge model. In this model, the contribution of the pressure of the cuttings in the excavation chamber on the working face stability is considered for both cases of α > 0 and α < 0. The optimization result is derived by applying limit equilibrium theory. A series of analyses reveal that the proposed model is predominantly influenced by the frictional angle and cover depth than by cohesion. The working face pressure increases linearly with the increase of α. In order to access the validity of the proposed model, the working face pressure and failure zone calculated by the proposed model are verified with numerical solutions and existing theoretical solutions. The current solution presents a more conservative result than other solutions in the case of α > 0, while predicts a smaller yet more reliable in the case of α < 0. Finally, two previous 1-g model tests with α = 15° and α = -15° are chosen to verify the proposed solution, where demonstrate a great consistence in limit working face pressure and the corresponding failure pattern.