Prediction of critical distance for tunneling with water-filled cavity ahead of tunnel face

In tunnel engineering, precise prediction of face stability can be challenging due to various influencing factors, particularly when tunnels are excavated under water-filled cavities. In this paper, a newly postulated failure mechanism composing of two logarithmic spirals truncated by the boundary of a water-filled cavity was adopted to determine the critical distance between tunnel face and the cavity. The upper bound solution of minimal safe distance, which plays an important role in the design and construction of deep tunnels, was obtained using upper bound theorem and optimization. A parametric study on the effect of corresponding parameters on face stability was also carried out. Limit analysis method was conducted to offer an alternative to investigate the incipient failure of tunnel face, so as to provide guidance to similar tunneling operations.