Abstract：Back pressure saturation method was commonly adopted to improve the saturation of samples, but specific provisions haven’t been given for the magnitude of back pressure in current Chinese standards. By employing the vertical-torsional coupling shear apparatus and the automatic true triaxial apparatus, the monotonic drained and undrained shear tests were carried out under different back pressures for the Fujian standard sands (with relative density as 30%, 58% and 70%, respectively) and fine sand, so that the stress-strain relationships for sandy soil and the development law for excess pore water pressure under different back pressures can be analyzed. The test results show that the back pressure has an obvious effect on the shear strength of dilatant sand in consolidated-undrained condition, and with the increase of dilatancy, the effect tends to be more evident; back pressure has no significant influence on both the undrained shear strength of shear shrinkage sand and the shear strength of sand in consolidated-drained condition, while it almost has no influence on the effective shear strength indexes of sand. According to this study, the obvious effect of back pressure on the shear strength of dilatant sand in consolidated-undrained condition may be attributed to the fact that with different back pressures, the bulk modulus of gas-liquid mixture in soil shall be different so that in the same volumetric expansion or in the same volumetric rebound, the induced excess pore water pressures shall be different, which may further directly affect the confining pressure and shear strength of sand. During the shear shrinkage process of soil, the closer the gas-liquid mixture approaches to a rigid body, the less the bulk modulus depends on the back pressure, so that in the shear shrinkage condition, the back pressure has no obvious effect on the stress-strain relationship and shear strength of sand. In the consolidated-drained tests, no matter how large the back pressure is, there is no excess pore water pressure, and the effective confining pressure is irrelevant to the back pressure so that the back pressure has no significant effect on the shear strength of sand in drained condition.
许成顺 耿 琳 杜修力 张 敏. 反压对土体强度特性的影响试验研究及其影响机理分析[J]. 土木工程学报, 2016, 49(3): 105-111.
Xu Chengshun Geng Lin Du Xiuli Zhang Min. Effect of back pressure on shear strength of sand: experimental study and mechanism analysis. 土木工程学报, 2016, 49(3): 105-111.
