Discrete Element Method Simulation Of Shear Band’s Development And Characteristic In Sand

Landslide is one of the worst geological disasters, thus analysis of the formation and development of landslide is always a focus of civil engineering. As the slope failure which cause the landside is closely related to the formation of shear band, it is very important to understand the formation and development of shear band.First, this thesis analyzes the formation and development of shear band in sand from several aspects such as velocity, displacement, rotation and force chain network by using PFC2 D to perform DEM simulation of biaxial compression test on sand. It also discuss briefly about the shear band’s inclination angle and thickness. By analyzing the strain localization through comparing the difference of porosity, coordination number and stress level between the granular system in shear band and that out of shear band, the inner mechanism of a shear band’s formation and development is revealed. Jamming and unjamming are employed in the analysis of shear band’s development and the quasi-solidliquid phase transition as a significant characteristic of a shear band’s development is verified.Then this thesis analyzes the influence of shear rate, friction coefficient and restitution coefficient in quasi-solid-liquid phase transition from several aspects such as stress, effective friction coefficient, coordination number, net contact time number, inertial number and volume change by using PFC3 D to perform DEM simulation of simple shear flow of sand under periodic boundary conditions. As a result, one can discover void ratio and shear rate will produce a noticeable effect while friction coefficient and restitution coefficient won’t. However, granular systems with larger friction coefficient or smaller restitution coefficient tend to consolidate while those with smaller friction coefficient or larger restitution coefficient tend to flow. What’s more, one can also find dense sand in simple shear flow under periodic boundary conditions will expand in volume accompanying by strain hardening while loose sand will shrink in volume accompanying by strain softening. Thus the periodic boundary conditions should be further examined, and one should use those boundary conditions cautiously.Finally, the - ?- phase transition diagram with void ratio e, shear stress , shear rate ? and the - - phase transition diagram with void ratio e, shear stress , smoothness coefficient are established. One can tell the state of a granular system under shear flow intuitively with these phase transition diagrams. The application of - ?- phase transition diagram in analyzing the development of shear band is also discussed.