In view of geologic origin

the span of saturated degree and matric suction of the gassy sand in Hangzhou metro(MTR) project are analyzed. The shear strength characteristics within the span of matric suction of the gassy sand are determined by GDS unsaturated triaxial system

and the shear strength index of the unsaturated gassy sand is obtained. The results show that the shear strength increases with the increase of matric suction of the gassy sand; and the influence on the shear strength is significant when the moisture content is greater than residual moisture content. The contribution of matric suction to the shear strength is not obvious when the moisture content is less than residual moisture content. The values from shear strength test and from predictive formula are compared and analyzed. Results show that the shear strength formula can be used to describe the strength characteristics of Hangzhou MTR gassy sand reasonably.