Non-Local THM Dynamics of Fractional Viscoelastic Marine Sediments with Imperfect Thermal Contact

During the operation of high-temperature subsea pipelines, marine sediments are subjected to complex thermo–hydro–mechanical (THM) interactions and high-frequency dynamic loading. Conventional THM models often fail to capture the full generality required to characterize these seabed responses, as they overlook microstructural size effects and soft clay rheology and assume idealized interfacial thermal contact. To address these limitations, this study proposes a unified non-local THM coupled dynamic model integrating non-local elasticity, fractional derivative viscoelasticity, and four distinct imperfect thermal contact conditions. Analytical solutions for temperature increment, excess pore water pressure and displacement in layered saturated porous media are rigorously derived. The framework assumes a one-dimensional, linear small-strain, fully saturated, and steady-state harmonic regime within homogeneous soil layers, and its validity is verified against an established analytical solution. Systematic parametric studies are performed to investigate the influences of the fractional order ratio (α(1)/α(2)), constitutive parameters (τσ/τε), and interfacial thermal resistance. The results indicate that when τσ/τε < 1, the resonance frequency shifts toward lower frequencies as α(1)/α(2) increases. Conversely, when τσ/τε > 1, the resonance frequency gradually increases, while the peak amplitude decreases. Moreover, interfacial thermal resistance significantly impedes heat transfer and induces pronounced localized temperature gradients. Neglecting these coupled effects may result in inaccurate predictions of the dynamic behavior of marine sediments.