Experimental research on behaviors of saturated sand subject to drained shear strength under complex stress conditions

The experimental tests of Fujian standard sand with relative density of 30 % are performed by using soil static and dynamic universal triaxial and torsional shear apparatus.A series of stress-controlled drained monotonic shear tests are conducted under complex stress conditions with constant mean principal stress.The coefficient of intermediate principal stress and orientation of principal stress are varied so that their coupled influences on shear behaviors of saturated sand are explored.Based on the comparative experimental results,under the same initial condition,coefficient of intermediate principal stress influences the stress-strain relationship of saturated sand,but does not make obvious effect on volumetric strain features.It is shown that the drained shear behaviors of sand are not dependant on consolidation stress ratio and considerably depend on coefficient of intermediate principal stress as well as orientation of principal stress.Furthermore,both coefficients of intermediate principal stress and orientation of principal stress affect friction angles at phase-transformation state(PTS) and at peak state.Finally,introducing a factor for weighing the influence of orientation of principal stress,and combining with the test results,an expression for strength indices taking coupled effect of coefficient of intermediate principal stress and orientation of principal stress into account is obtained by using generalized twinshear stress criterion.