Characteristics of mud and water inrush disasters in high water pressure filled karst tunnels and the evolution law of surrounding rock response

The filled karst cavity ahead of the tunnel face, under high water pressure, is prone to mud and water inrush, posing a threat to tunnel construction safety. It is imperative to investigate the disaster characteristics of mud and water inrush in high water pressure filled karst tunnels and the evolution law of surrounding rock response. Firstly, the model test design and working condition settings were carried out, and a three-dimensional model test system was constructed to explore the influence characteristics of the anti-outburst rock mass thickness on the seepage evolution at the tunnel face of high water pressure filled karst tunnels. On this basis, the stress redistribution of the anti-outburst rock mass and the deformation mechanism of the tunnel face were revealed. The results show that: For high water pressure filled karst tunnels, the instability characteristics of the surrounding rock can be divided into three stages: the expansion of seepage channels, local failure, and overall instability. The thickness of the anti-outburst rock mass constrains the deformation and failure characteristics of the surrounding rock. Thicker rock masses primarily undergo overall compressive deformation, whereas when approaching the critical safety thickness, the failure mechanism shifts to bending deformation and local tensile cracking. During tunnel excavation, the failure of the anti-outburst rock mass initiates at the bottom with stress concentration, progresses to cracking in the mid-section, and culminates in penetration at the top, ultimately leading to overall collapse. When the anti-outburst rock mass thickness is 6 cm and the karst cavity water pressure is in the range of 10.5 kPa to 13.5 kPa, the distribution patterns of earth pressure and water pressure within the rock mass reveal the transformation of preferential seepage paths as well as the initiation and development of cracks. When the anti-outburst rock mass thickness is 2 cm, the tunnel face undergoes sudden collapse after a brief period of stability.