Undrained heating effects on monotonic shear behaviors and critical cyclic stress ratios of deep-sea sediment

A series of temperature-controlled triaxial tests are conducted on the deep-sea sediment from the Western trough of the South China Sea. The undrained heating effects on undrained shear strength, pore pressure and critical cyclic stress ratio are discussed. Based on the Yao's theoretical framework, the expression for temperature-induced excess pore pressure is given, and then the relationship between the undrained shear strength and the critical cyclic stress ratio is discussed. The test results indicate that the temperature-induced excess pore pressure leads to the decrease of the effective stress, weakens the undrained shear strength, and results in quasi-overconsolidated mechanical properties. The development rate of accumulated strain increases noticeably under cyclic shear conditions as the temperature rises, but at the initial shear stage, the high temperature prevents the development of excess pore pressure, even leads to a negative value. The approach for calculating the threshold cycle stress ratio based on the production of the normalized excess pore pressure is inapplicable. It is proposed that the development trend of the accumulative strain and excess pore pressure should be fully considered when determining the limiting cycle stress ratio of quasi-over consolidated samples. The shear strength and critical cyclic stress ratio decrease with the increasing temperature which should be fully considered in engineering.