Effect of Stress Paths on Shear Strength Response of Unsaturated Gassy Sand from Hangzhou Metro Project

To study the effects of stress paths on shear strength characteristics of unsaturated sand, a series of conventional triaxial compression (CTC), reduced triaxial compression (RTC), and reduced triaxial extension (RTE) tests were conducted on shallow gassy sand from the Hangzhou Metro project, China. Tests were carried out by using a stress path unsaturated triaxial test system, capable of reproducing stress paths that are normally induced on soils in subway construction projects. Results show that the stress-strain relationship of unsaturated sand under various stress paths has different characteristics and the strength parameters are closely related to the particular stress path followed. Effective cohesion and apparent cohesion are affected significantly by the stress path, but effects on the internal friction angle are not important. Relationships between apparent cohesion and matric suction from various stress paths induced on unsaturated sand can be described via power functions. A unified shear strength model was then devised for gassy sand along different triaxial stress paths.