Assessment of Hard Rock Tunnel Stability: A Note on the Influence of Post-peak Strength Degradation

Abstract

Tunnelling depth is increasing rapidly in Taiwan. The effect of brittle failure on hard rock tunnelling is, however, rarely studied. For this, in this paper, a study is carried out on the post-peak form of the Hoek-Brown failure criterion and the strength loss experiment, whereby a relationship between strength loss parameter and confining stress is established. Subsequently, a numerical analysis model, so-called strength degradation model, is proposed and applied to predict the impact of the post-peak strength degradation on an actual tunnel. The analysis shows that the effect of the post-peak strength degradation on excavation deformation is becoming more and more pronounced with increasing depth. Severe excavation deformation may endanger tunnel stability during construction in deep overburden. The strength degradation beyond brittle failure shall play an exceptionally important role in the stability of deep tunnelling.