Analysis of interaction between tunnel support system and surrounding rock for underwater mined tunnels considering the combined effect of blasting damage and seepage pressure

When an underwater tunnel is constructed using the drill-and-blast method, the rock mass around the tunnel undergoes significant blasting damage. Quantifying the combined effect of blasting damage and seepage pressure on the support–surrounding rock interaction is critical for an underwater mined tunnel. An analytical model is proposed to analyze the entire process of support-surrounding rock interaction in an underwater mined tunnel considering the combined effect of blasting damage and seepage pressure. First, the ground reaction curves are derived considering the combined effect of blasting damage and seepage pressure. Four configurations according to the distribution of plastic zone in the damaged and undamaged zones are distinguished and solved. Subsequently, the fictitious pressure, which is introduced to quantify the spatial effect of tunnel face, is also solved. Thereafter, combining Hoek’s longitudinal displacement profile expression and the proposed ground reaction curve solution, an analytical algorithm for the support–surrounding rock interaction is proposed. The tunnel displacement and support pressure during the entire process of support–surrounding rock interaction are obtained, which are in agreement with the 3D numerical simulations and field monitoring results. Compared with the conventional convergence-confinement method, the performance and advantages of the proposed method are demonstrated. The proposed method is feasible with higher confidence for the preliminary design of underwater mined tunnel, particularly for tunnels excavated in weak zones.