Discrete Element Analysis On Shear Tests And Cone Penetration Tests Of Cohesionless Granular Materials

DEM has proven to be a powerful and versatile method to analysis the mechanical behavior of granular materials during shear tests. But there are some problems still confusing researchers, for example, the influence of sample size, interparticle friction and strain rate on shear resistance.By performing a series of numerical triaxial compression tests, and analyzing the tests from a microscopic viewpoint such as the spatial distribution of contact vectors, the following conclusions can be obtained:â—‹1Due to the effects of boundary friction, shear resistance changes with increasing specimen size, and the effects of boundary friction can not be eliminated until the specimen is large enough: when the characteristic length ratio L/R>30, the variance of shear resistance results from changing specimen size is smaller than 10%;â—‹2 What's more, shear resistance of small size specimens scatters largely, for granular fabrics of these specimens differ a lot;By performing a series of numerical biaxial compression tests, and analyzing the tests from a microscopic viewpoint such as the spatial distribution of frictional works and rotational kinetic energy, it concludes: shear resistance increases non-proportionally as interparticle friction increases: shear resistance increases rapidly in the low interparticle friction regime and levels off in value when interparticle friction is large. This phenomenon is explained in this paper by considering the movement mechanisms of the particles;The results of another series of numerical biaxial compression tests indicates that, larger strain rate leads to larger average stress level in the particle assembly. And this can help us to understand why tests with larger strain rate result in larger shear resistance.A combined theoretical and numerical approach has been employed to investigate the feasibility of obtaining in-situ horizontal stress from cone penetration test.Based on the work of predecessors, an analytical solution for cavity limiting pressure and penetration resistance is obtained. Also a series of numerical penetration tests have been conducted to investigate the influence of in-situ horizontal stress on penetration resistance. At last, the evolution of main stress field, velocity field, void ratio field and particle rotation field are studied to illustrate the penetration mechanism.