Stability of surrounding rock in karst formations and response mechanism of tunnel linings under high water pressure

Abstract

Under certain natural conditions, karst stratum tunnels may experience the buildup of water pressure behind their linings, which can jeopardize operational safety. Therefore, it is crucial to examine the distribution of water pressure and the structural response characteristics in karst strata tunnels under high water pressure environments. Firstly, a three-dimensional model test was constructed to reveal the influence mechanisms of cavity location and water pressure on the distribution characteristics of water pressure behind the tunnel lining, the stress state of the tunnel support structure, and the surrounding rock pressure. Building upon this, a numerical model was employed to further elucidate the characteristics of stress and deformation evolution in the lining under complex water pressure environments. The results indicate that: When cavities are located above or below the tunnel, the stress and deformation of the lining exhibit symmetry; cavities located directly above the tunnel pose the most unfavorable condition for the lining structure, with the safety coefficient at the vault being approximately 30 % of that for cavities located to the side or below under identical hydraulic head conditions. The eccentric stress state of lining cross-sections is closely related to the cavity location; sections distant from the cavity consistently experience eccentric tension and exhibit lower safety coefficients than other sections. The failure process of the lining under high water pressure can be divided into four stages: water seepage, crack initiation, crack propagation, and localized failure. The displacement of the lining presents a ‘cherry-shaped’ distribution with the concave side pointing towards the karst cavity. The closer the karst cavity is to the vault, the greater the deformation. For every 0.5 MPa increase in water pressure from 0.5 MPa to 3 MPa, the vault displacement increases from 0.85 mm to 18.12 mm, with growth rates of 158 %, 144 %, 72 %, 46 %, and 35 % respectively. The Mises stress within the lining forms a ‘maple leaf’ distribution, with a pronounced stress concentration in a 120° sector adjacent to the karst cavity.