Abstract: Understanding the mechanical changes of marine soft soil under temperature is crucial for the construction and long-term operation of submarine pipelines. A series of basic physical and mechanical properties tests was carried out on the marine soft soil in Shanwei, Guangdong province. X-ray diffraction, X-ray fluorescence spectrometry, and scanning electron microscopy were employed to achieve the marine soft soil’s mineral composition, element composition and microstructure. The consolidated undrained laboratory tests under isotropic consolidation and biaxial consolidation conditions were carried out using a temperature-controlled triaxial apparatus. The test results revealed significant findings. Firstly, when the axial strain is small, the undrained shear characteristics of saturated marine soft soil are influenced by the ambient temperature and the consolidation stress ratio. Specifically, a higher ambient temperature or a smaller consolidation stress ratio results in a greater secant modulus. The secant modulus exhibits an inverse relationship with the consolidation stress ratio and demonstrates a power function relationship with the ambient temperature. As the axial strain increases, the peak strength of the soil is affected by both ambient temperature and consolidation stress ratio, while the peak pore pressure is less affected by ambient temperature. Furthermore, the initial dry density of the sample was found to impact the undrained shear characteristics of the isotropic consolidated soil (K_c=1.00). A greater initial dry density resulted in a smaller peak pore pressure, a greater peak strength, and a more significant decrease in peak strength with rising temperature. Additionally, the consolidation stress ratio was observed to affect the peak strength and effective stress path of saturated marine soft soil under different ambient temperatures. Specifically, when K_c=1.00 or 0.67, an increase in the ambient temperature softened the saturated marine soft soil; whereas when K_c=0.50 or 0.40, the rise in ambient temperature hardened the soil.

Key words: marine soft soil, physical and mechanical parameters, microstructure, triaxial test, temperature effect