Research on the swelling characteristics of rich-water layer slate in tunnels and catastrophic instability prediction under blasting

Purpose This paper aims to address the instability issue of water-rich layered rock mass tunnels under blasting and swelling effects, lateral confinement swelling tests on water-rich slate are conducted to reveal the argillization and swelling characteristics as well as the variation laws of slate. Based on the surrounding rock instability characteristics of water-rich layered rock, a tunnel mechanical model is established. Design/methodology/approach In this paper, the swelling characteristics of water-rich slate are studied by laterally constrained swelling test. Based on the mechanical model of layered rock, the instability criterion of tunnel blasting is established, and the reliability of the criterion is verified by engineering application. Findings The smaller the layer inclination angle, the larger the contact area between clay minerals in the slate and water, and the stronger the water absorption capacity of the rock sample, which leads to greater swelling pressure and swelling deformation. Based on the mechanical model of layered rock, the instability criterion of tunnel blasting is established, and the reliability of the criterion is verified by engineering application. Originality/value Based on the layered rock mechanics model, considering the expansion effect of the rock mass and the deterioration effect of blasting, the criterion for tunnel blasting instability in water-rich layered rock masses was constructed using the point singularity theory. The influences of tunnel width, the expansion effect of slate, and the blasting deterioration effect on the stability of the tunnel were discussed.