The Thermo-mechanical Behaviour of Clay in Different Stress and Temperature Paths

During the service period of oil-gas pipelines, marine cables and energy pile, the surrounding soil will be strongly influenced by the high temperature, which changes the mechanical properties (strength and stiffness) of the surrounding soil and causes additional deformation, and ultimately leads to instability of the structure. As the submarine oil-gas pipeline are always shallow buried, where the seabed soil at the top of the surface is generally overconsolidated. Therefore, the undrained shear behaviour of overconsolidated clay is of great important in submarine pipeline design considering the global buckling. In this study, the undrained shearing behaviour of kaolin under different overconsolidation ratios (OCR = 1, 2, 4) and different heating paths are carried out based on the temperature-controlled triaxial system. For normally consolidated kaolin, the test results show that under drained heating, the undrained shear strength is increased approximately 20% with the increasing temperature from 20 °C to 55 °C; after a heating-cooling cycle (20 °C–55 °C–20 °C), the undrained shear strength is still 10% higher than the strength in room temperature 20 °C, which indicates that the soil strength is influenced by the temperature history. For overconsolidated kaolin, the undrained shear strength is weakly influenced by the temperature. The temperature has a weak effect on the final pore pressure in undrained shearing process, both for normally consolidated and overconsolidated kaolin. The slope M of the critical state line will be affected by the temperature, which increases from about M(20 °C) = 1.00–1.05 to M(55 °C) = 1.11–1.18. More interestingly, the M value for kaolin after heating-cooling cycle (20 °C–55 °C–20 °C) is consistent with the value in high temperature (55 °C), which means the slope M of the critical state line is dependent on the temperature history.