Interfacial constraint effects of waterproofing layers on temperature‐induced early cracking in high geothermal conditions

Abstract Early cracking in tunnel secondary lining concrete poses serious risks because of temperature stresses arising from hydration heat, geothermal energy, and interfacial constraints. The influence of waterproofing layer constraints on temperature‐induced cracking in high geothermal environments was evaluated. Contact properties of spray‐applied waterproofing membranes were determined via shear and tensile tests using a cohesive zone model and then incorporated into an ABAQUS simulation that couples thermal and stress fields. Results indicate that when primary and secondary linings are in direct contact, tensile stresses may reach 1.43 MPa at 25°C, exceeding the 3‐day concrete tensile strength of 0.98 MPa and triggering cracking. In contrast, the use of a sheet waterproofing membrane significantly reduces tensile stress. Sensitivity tests reveal that increasing spray‐applied membrane stiffness from 1 to 100 times raises tensile stress from 0.02 to 1.36 MPa at 25°C, with similar trends observed at 70°C, while the constraint effect nearly vanishes upon shear failure of the membrane. These quantitative findings provide practical guidance for optimizing waterproofing strategies to mitigate early‐age cracking in tunnel linings.