DEM simulations of anisotropic structured sand with different deposit directions

In order to study the effects of deposit directions on the mechanical response of anisotropic structured sand, two anisotropic pure sand samples deposited in horizontal and vertical directions are prepared by using elliptical particles in NS2D first, and then a bond contact model considering the bond thickness is implemented into the pure anisotropic sand samples to prepare anisotropic structured sand samples. Biaxial compression tests are conducted on both samples, and the results of samples with horizontal deposit direction are compared with the laboratory test results to validate this model, then the results of two samples with different deposit directions are compared to study the effect of depositing direction. Test results show that strain softening and shear dilation occur in both samples. The peak deviator stress of the horizontal deposited sample is larger than that of the vertical deposited sample, while the residual shear forces are nearly the same. Besides, the critical void ratio of the horizontal deposited sample is larger than that of the vertical deposited sample. The changes of bond breakage percentage and bond breakage ratio of these two samples are of the same and are consistent with the stress-strain and volumetric mechanical responses. The number of bond contacts decreases in the two samples, and the bond contacts distribute in a vertical principal direction in the horizontal deposited sample and a horizontal principal direction in the vertical deposited sample during the tests. The principal direction of particle orientation is horizontal for the horizontal deposited sample throughout the tests, while the principal direction of particle orientation in the vertical deposited sample is firstly vertical and then develops towards an isotropy state.