Experimental study on stress path of sand based on digital image processing technique

The triaxial equipment of GDS is improved based on the digital image processing technique, and the failure process and shear band mode of medium sand under different stress paths are studied. Thirteen monotonic shearing tests are performed, including isotropic stress consolidation and anisotropic stress consolidation. Deformation characters and strain fields of sample surface at different time during triaxial compression progress are recorded, and the failure progress of samples is presented. The results show that, under different stress paths, the failure progress of samples is closely related to the stress path. Different realizing ways of increasing pore pressure and decreasing the total stress for the same stress path may lead to different results. The final failure mode can be divided into three kinds, namely uniform bulging, single shear band and cross shear band. The effective stress ratio regularity shows that the higher stress ratio of consolidation, the lower value of effective stress ratio and the bigger value of reduction after peak value. The failure mode is initially determined before the peak value of effective stress ratio, macro stability is reached after the peak value.