Study on Variation Characteristics of Shear Strength of Deep-Sea Sediments in the South China Sea Under Thermo-Hydraulic Coupling

Abstract This study focuses on the unique physical-mechanical properties and special occurrence environment of deep-sea sediments in the South China Sea. Through gradient-controlled triaxial shear tests, it systematically reveals the mechanical response mechanisms of these sediments under the dual-field coupling effects of water content (15%-35%) and temperature (4°C-60°C). The research confirms that increased water content significantly reduces the undrained shear strength of sediments through water film lubrication and pore water pressure accumulation. Temperature rise leads to simultaneous weakening of cohesion and internal friction angle, attributed to low-temperature stabilization of cement crystallization and pore water viscosity enhancement, while high temperature induces cement phase softening and intensified particle thermal vibration. Although confining pressure elevation can enhance lateral constraint effects, it cannot fully counteract the dominant influence of combined water-thermal deterioration. The improved thermo-hydro-mechanical coupling model, established based on experiments, achieves accurate prediction of mechanical behavior under multi-field coupling conditions (R²>0.95) by quantifying the nonlinear relationship between temperature sensitivity coefficients and water content gradients. This provides quantitative theoretical support for submarine geological safety prediction, optimized design of marine resource development, and risk control for long-term service of offshore platforms.