Analysis on the Instability of Interlocking Arch Induced by Water–Sand Outburst in Tunnel Lining Cracks

The phenomenon of water–sand outburst often occurs when the tunnel passes through the sand texture layer. In the process of water–sand outburst, the sand bodies of large particles are accumulated above the cracks of the tunnel under the squeezing effect of each other, and the phenomenon of particle arching occurs, thereby forming a stable contact force arch. With the diameter of the tunnel cracks increases, stable contact force arches cannot be formed between the sand particles. In this paper, by analyzing the occurrence mechanism of water–sand outburst disasters, three arrangement models of particles were established when the interlocking arch was formed, and the critical ratio of cracks to particles when the force arch was destroyed was obtained by theoretical derivation. The results show that the critical ratio was only related to the internal friction angle of the sand body itself. When the ratio of cracks to particles does not exceed the critical ratio, a stable contact force arch will be formed, and the continuous water–sand surge will not be induced basically; once the ratio of cracks to particles exceeds the critical ratio, stable contact arches will not be formed. Unstable contact force arch can easily induce water–sand outburst disasters. As the ratio of cracks to particles increased, the damage degree of water–sand outburst disaster increased.