Analysis of Interlayer Stress Transfer Mechanism of Bimetallic Composite Pipes

Addressing the ill-defined interlayer stress transfer mechanisms and the risk of stress exceeding material limits in bimetallic composite pipes under landslide hazards in high-steep mountainous regions, this study establishes a refined pipe–soil interaction finite element (FE) framework. Built upon a previously validated coupled model, interlayer interfacial contact formulations were enhanced, and valid operating regimes were systematically screened using the ultimate tensile strength (UTS) as the structural failure criterion. The regulatory impacts of soil displacement, internal operating pressure, and base pipe wall thickness on interlayer stress transfer efficiency were quantitatively mapped. The results demonstrate that within the valid service window, the interlayer stress transfer coefficient continuously escalates with soil displacement, identifying 3 m as the critical displacement threshold for base pipe yielding. Elevating internal pressure increases the stress transfer coefficient, which is mainly dominated by the high sensitivity of the thin liner’s membrane stress to internal pressure, and is secondarily promoted by the enhancement of interfacial shear capacity caused by increased contact pressure. Crucially, increasing the base pipe wall thickness from 12 mm to 15 mm effectively reduces the peak stress of the base pipe from 440.5 MPa to 310.2 MPa within the safe operational regime (1 m displacement) while systematically lowering the interlayer stress transfer coefficient η from 0.84 to 0.78 at the 3 m critical yielding threshold. This structural shielding effect is fundamentally driven by the enhanced structural stiffness (flexural rigidity) of the outer base pipe, which directly absorbs the primary geotechnical bending load and consequently lowers the deformation demand transmitted across the interface. Ultimately, this work unveils the core interlayer transfer mechanism characterized by “base-pipe stiffness dominance, interfacial shear transmission, elastic modulus mismatch governing stress allocation, and deformation compatibility steering load pathways,” providing a robust theoretical foundation for the interfacial integrity design of bimetallic composite pipelines in landslide-prone mountainous environments.