A Comparative Study on Monotonic Shear Behaviors of Granular Soils Under Different Drainage Conditions

Abstract

Various stress-controlled drained and undrained monotonic shear tests on the Chinese Fujian standard sand of relative density 30% under complex initial consolidation conditions with different stress paths are conducted by using the soil static and dynamic universal triaxial and torsional shear apparatus. The mean principal stress is controlled unchanged in the process of tests. The coefficient of intermediate principal stress and orientation of principal stress are varied so that their influences on shear behavior and strength of saturated sand under different drainage conditions are respectively explored. It is shown through comparison that coefficient of intermediate principal stress influences the stress-strain normalization relationship, but does not make obvious effect on volumetric deformation as well as pore-water pressure. Under the same initial condition, the deviator stress ratio reduces with increase of coefficient of intermediate principal stress. The above-mentioned phenomena do not relate to the drainage condition. Orientation of principal stress also influences remarkably on monotonic shear features of sand. In drained tests, variation pattern of stress-strain relationship which is associated with the orientation of principal stress depends on shear stresses on horizontal plane and vertical plane. Furthermore, the deviator stress ratios (or the frictional angles) at phase transformation state and at peak state are all parabolically related with orientation of principal stress. In undrained tests, the effective deviator stress ratio attained at peak state reduces gradually with increase of orientation angle of principal stress. Meanwhile, for different orientation of principal stress, the shear strength indices obtained in the tests are affected by the variation of drainage conditions.