Influence mechanism of initial mechanical damage on concrete permeability and tunnel lining leakage

The stress state is not effectively considered in existing studies when researching the permeability evolution of concrete with initial mechanical damages, causing ambiguity in the influence mechanism of initial mechanical damage on tunnel lining leakage. This deficiency can lead to significant uncertainty in predicting the probability and evaluating the consequences of tunnel leakage diseases, further affecting the formulation of relevant prevention strategies. Therefore, mechanical damage is induced to concrete specimens by subjecting them to certain stress levels, and triaxial compression seepage tests are subsequently conducted to study the influence of initial mechanical damage on permeability evolution and macrocracks. Furthermore, the relationship between microcrack characteristics and concrete permeability is studied, ultimately revealing the influence mechanism of initial mechanical damage on tunnel lining leakage. Research results indicate that the concrete permeability decreases first, becomes stable, and then continuously increases during testing, and is positively related to changes in horizontal deformation ratio. When the damage-inducing stress reaches 80% of the uniaxial compressive strength (UCS), the impact of initial mechanical damage on concrete permeability increases significantly. The increase in initial mechanical damage can lead to a significant rise in permeability, even when the crack volume is in a compacted state. Additionally, cracks on the surface of the specimen become clearly visible when the test terminates, once the damage-inducing stress reaches 85% UCS. Two factors contribute to the gradual increase in concrete permeability with the rise in initial damage-inducing stress. Firstly, microcracks inside the concrete gradually widen and propagate. Secondly, the microcracks resulting from the initial damage progressively enlarge due to water pressure during the triaxial compression seepage test. Influenced by the blockage of seepage channels, concrete permeability can occasionally decrease during testing. The accidental load induces the gradual propagation of microcracks inside the mechanically damaged concrete. Then, the rebound deformation of concrete after the removal of the accidental load causes the closed microcracks to reopen significantly, leading to an increase in permeability and subsequent tunnel lining water leakage.