Face stability analysis of shallow underwater tunnels in fractured zones

Abstract

When an underwater tunnel constructed via the mining method crosses a fault fracture zone, one of the most important issues to consider is ensuring the stability of its face. Several auxiliary techniques have been adopted in construction; however, the design parameters of these auxiliary measures are mainly determined by experience. In this study, a stability analysis model of the working face of an underwater tunnel constructed via mining method in a fractured zone was established by considering the effect of groundwater seepage force. Afterward, the corresponding formula was determined. By considering a pre-support pipe roof and an advanced grouting ring as a beam on the elastic foundation, the corresponding stability analysis model and computing method under pre-reinforced condition were built. In addition, an engineering example was analyzed. Results show that the stability coefficient of the tunnel face is only 0.77 without the pipe roof and advanced grouting. Meanwhile, the stability coefficient increases to 2.47 under pre-reinforced condition. This finding indicates that a tunnel must be reinforced in advance in a fractured zone to ensure safe construction. The influences of pre-reinforcement parameters (i.e., thickness, cohesion, and internal friction angle of the grouting circle) on the stability of the tunnel face are discussed at the end of the article.