Inverse reliability-based design of limit support pressure for tunnel face stability

The possibility of reliability-based design (RBD) for shallow circular tunnels is explored using the simplified inverse first-order reliability method (FORM). The inverse reliability analysis can directly offer some design information that meets the targeted reliability index, and the calculation procedure can be easily implemented in the original space of random variables. In the tunnel face stability analysis, the deterministic results of the support pressures are obtained through the three-dimensional finite element limit analysis (FELA), and the limit state functions are established for the collapse and blow-out failure modes of the excavated face, respectively. In the probabilistic study, the inverse reliability method shows adequate accuracy by comparing with Monte Carlo simulations. On this basis, a series of probability analysis and RBD of the limit support pressures for maintaining the tunnel face stability in cohesive soil and sandy soil strata are carried out. Some insightful RBD results are obtained with respect to different scenarios of shear strength uncertainties. Finally, the effects of spatial variability of shear strength parameters of soils on the required support pressures of tunnel face are discussed.