Hydro-splitting off analysis on underground water in deep-lying tunnels and its effect on water gushing out

Abstract

The mechanism of water gushing in jointed surrounding rocks of deep-lying tunnels is studied. The results show that a hydro-splitting course under high water pressure is involved just before water gushing out, which can be described by a fracture model with a joint and type II failure. According to the criterion of fracture instability, a formula of critical water pressure resulting in hydro-splitting is derived. Also, the spacing variation of a joint under high pore water pressure during water gushing is especially regarded. An equation is put forward to describe the joint spacing variation (Δb) based on the deformation of joint walls. As an example, the case of Jinping deep-lying tunnel is discussed. It gives a reasonable explanation to the high pressure water gushing encountered in this project.