Contribution to the Micromechanical Analysis of Oedometric Modulus and Damping Ratio in Granular Compression Wave Propagation in Granular Medium

Objective This study investigates the micromechanical behaviour of compression wave propagation in granular media using the Discrete Element Method (DEM), with a focus on the evolution and degradation of the oedometric modulus and the damping ratio under harmonic excitation. Methods A C++ DEM model was developed to simulate wave propagation in a granular deposit subjected to base excitation. The formulation explicitly incorporates nonlinear contact mechanics, interparticle friction, and energy dissipation under rigid-base, free-surface, and horizontal periodic boundary conditions. A three-phase loading protocol, comprising a 4.5-second amplitude ramp-up, a 6-second steady-state harmonic phase, and a 1.5-second ramp-down phase, was used to distinguish transient and steady-state responses across varying deformation amplitudes and confining pressures. Results The results demonstrate significant degradation of the oedometric modulus and a progressive increase in the damping ratio with increasing deformation amplitude, whereas higher confining pressures enhance the overall stiffness of the granular deposit. Compression waves exhibit lower damping and less degradation of the oedometric modulus than shear waves. Quantitatively, the free-vibration analysis provides an upper-bound estimate of stiffness with a fundamental frequency of 59.62 rad/s , a wave velocity of 20.49 m/s , and a maximum quasi-elastic modulus of 83.8×10 4 Pa . Conversely, the secant modulus derived from low-amplitude stress-strain hysteresis loops yields lower values of 82.7×10 4 Pa , inherently accounting for interparticle sliding and frictional dissipation, thus indicating that stiffness degradation initiates at sub-yield strain levels. Discussion In contrast to continuum-based approaches, this discrete framework elucidates the grain-scale mechanisms underlying the macroscopic dynamic behaviour of granular materials, highlighting the critical influence of the evaluation procedure on the determination of nonlinear soil parameters. Conclusion The DEM model provides a micromechanical interpretation of compression wave propagation in granular soil. Free-vibration analysis provides an estimate of elastic stiffness, whereas hysteresis loops capture dissipative mechanisms and consequently yield lower stiffness estimates. This distinction is important for geotechnical and seismic response analyses.