Rotational failure mechanisms for the face stability analysis of tunnels driven by a pressurized shield

TLDR

The study aims to determine collapse and blow‑out face pressures for a circular tunnel driven by a pressurized shield and to extend the collapse mechanism to include a tension cut‑off in the Mohr–Coulomb criterion. The authors use a kinematical limit‑analysis framework, proposing two rotational failure mechanisms for active and passive cases, generating a 3‑D failure surface point‑by‑point via spatial discretization, and extending the collapse mechanism to incorporate a tension cut‑off in the Mohr–Coulomb criterion. The proposed mechanisms better account for the entire circular tunnel face, align with experimental rotational rigid‑block movement, and yield significant performance gains over translational mechanisms in frictional soils. © 2010 John Wiley & Sons, Ltd.

Abstract

Abstract The aim of this paper is to determine the collapse and blow‐out face pressures of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of the limit analysis theory. Two rotational failure mechanisms are proposed for the active and passive cases. These mechanisms have two significant advantages with respect to the available ones: (i) they take into account the entire circular tunnel face instead of an inscribed ellipse to this circular area, and (ii) they are more consistent with the rotational rigid‐block movement observed in the experimental tests. For both the active and passive cases, the three‐dimensional failure surface was generated ‘point by point’ instead of simple use of the existing standard geometric shapes such as cones or cylinders. This was achieved by employing a spatial discretization technique. The numerical results have shown that the present rotational mechanisms provide, in the case of frictional soils (with or without cohesion), a significant improvement with respect to the translational mechanisms. Finally, an extension of the proposed collapse mechanism to include a tension cut‐off in the classical Mohr–Coulomb failure criterion is presented and discussed. Copyright © 2010 John Wiley & Sons, Ltd.