Abstract: Different from the typical stress path often used in triaxial or plane strain test, a stress path with decreasing confining pressure was applied to plane strain compression test on Toyoura sand. Influence of initial consolidation pressure and initial relative density of sand specimen was investigated. By using the 2D digital image correlation(DIC) method, shear band formation process was analyzed. Shear band thickness and inclination angle, as well as their influencing factors were analyzed quantitatively. Study results show that shear band in the Toyoura sand appeared before the peak shear strength. For dense Toyoura sand, with increasing confining pressure, shear strength(principal stress ratio) decreases and its peak value appears later; shear band thickness is smaller but shear band inclination angle change is not obvious. With increasing relative density, peak shear strength increases and appears at an earlier strain; shear band thickness becomes smaller while shear band inclination angle becomes higher. Moreover, the Coulomb’s equation based on the peak internal friction angle can relatively accurately predict the maximum shear band inclination angle of Toyoura sand under plane strain compression.

Key words: sand, plane strain compression, stress path, digital image correlation(DIC), shear band