Experimental study on asymptotic behaviour of anisotropic sand

Asymptotic behavior is one of the important mechanical characteristics of sand. Anisotropy and its effect on the asymptotic behavior of sand are investigated by use of a series of triaxial drained shear tests and strain paths tests. Studies show that when the ratio of lateral to axial strain increment is one, the axial stress isn’t equal to the lateral one, which can be called anisotropy of compression deformation. And anisotropic shear strength due to anisotropic alignment of particles can be seen clearly in the strain paths tests where the strain increment ratio is small enough to cause the soil failure. When the sand is loaded along the constant strain increment ratio paths, the ratio of lateral to axial stress will eventually approach a constant value, i.e. the asymptotic stress ratio. And the asymptotic stress ratio is a little larger for the specimens with vertical bedding plane than that with horizontal one. When the shear deformation of soil is small, the difference between the measured asymptotic stress ratio and that predicted by the isotropic asymptotic state criterion is large, but it gradually decreases with the increase of the shear deformation. The effect of anisotropy on the asymptotic stress ratio is investigated on the basis of strain paths tests on different anisotropic materials. Furthermore, the asymptotic behavior of anisotropic sand is discussed and an equation is formulated to quantitively determine the relationship between the asymptotic stress ratio and the strain increment ratio for anisotropic sand.