Abstract:

In the seismic exploration, effective medium theories based on Hertz-Mindlin equivalent medium model were often used to predict the seismic elastic properties of unconsolidated sands. But those theories often give relative larger shear modulus comparing to measured data. By using 3D discrete element simulation, a series of uniaxial compression and pure shear test were carried out on granular material for the sake to study the insufficiencies of those effective medium theories from the level of microscale of particle size and mesoscale of force chain. The simulation result indicates that stress relaxation getting from the rotation and rearrangements of particles has neglect influences on the calculation of bulk modulus. But the stress relaxation has significant influences on the calculation of shear modulus under the shear stress perturbation. Shear stiffness calibration factor (C) and combined parameter R/R were advocated to calibration those effective medium theories based on Hertz-Mindlin equivalent medium model to accounting for the influence of relaxation in contact area and grain angularity.

Key words: sand, relaxation, discrete element, Hertz-Mindlin equivalent medium model, elastic moduli