Dynamic response characteristics, load-bearing efficiency in multimaterial tunnel assemblies subjected to recurrent intense fluid loading

A multilayer lining concept is proposed to mitigate hydraulic leakage risk and loss of load-carrying capacity after cracking in reinforced-concrete tunnels, while also reducing instability concerns typical of metal liners under elevated external pressures. The configuration comprises an inner reinforced-concrete ring, an intermediate steel plate, and an outer concrete ring, forming a cooperative load-resisting assembly. Physical model tests were carried out under alternating external and internal pressurization to quantify circumferential stress evolution and the associated load-transfer path. Under external pressurization, the inner concrete, steel plate, and outer concrete sustained approximately 40%-42%, 13%-16%, and 43%-45% of the resultant hoop action, respectively, and the steel plate remained substantially below the buckling demand, indicating a stable compression regime within the tested range. Under internal pressurization, progressive cracking of the concrete rings triggered a marked redistribution of hoop force toward the steel plate; its load fraction increased from 15% to 25% following inner-ring cracking and from 14% to 26% following outer-ring cracking. Across the two pressurization cycles tested, the steel plate maintained the capacity to carry alternating tensile-compressive demands, thereby preserving global integrity after concrete damage. Overall, the proposed multilayer lining exhibits improved resistance to limited-cycle hydraulic loading and enhanced structural robustness relative to conventional lining schemes, supporting its applicability to high-head conveyance tunnels.