Numerical Simulation of Undrained Triaxial Test Using 3D Discrete Element Modeling

A series of undrained triaxial tests were performed on coarse aggregate using discrete element model. In order to take the shape of grains, each particle is formed by clumping two equal-sized particles together. The distance between the centers of two particles is equal to 1.0 times the particle radius. The numerical model of coarse aggregate is generated, and the desired porosity is obtained by a radius expansion method. Using numerical undrained triaxial tests the micro-mechanical properties of the numerical material are calibrated in order to match the macroscopic response of the real material. Numerical simulations are carried out under the same conditions as the physical experiments (porosity, boundary conditions and loading). The peak stress and pore water pressure behavior of the numerical material is studied. The relationship between macroscopic mechanical properties and microscopic parameters such as contact orientation and contact forces can be achieved in this way. The calibration procedure reveals that the peak stress of the coarse aggregate sample depends not only on local friction parameters but also on the shear modulus and Poisson's ratio. The larger the value of the applied shear modulus, the higher the resulting stress peak. Furthermore, the pore water pressure response depends strongly on local friction. The numerical results are quantitatively in agreement with the laboratory test results.