Modeling the effect of matric suction on a spherical particle mixture using discrete element method in PFC 3D

Unsaturated soils and granular materials play a pivotal role in geotechnical and environmental engineering, with water under tension markedly influencing their mechanical behavior, particularly strength and deformation. To elucidate the impact of matric suction on the macroscopic mechanical response, this study presents a modeling approach for capillary interactions between spherical particles in a partially saturated medium using the Discrete Element Method (DEM). The PFC3D software is employed to calibrate mesoscale interparticle contact parameters to replicate uniaxial compression tests performed on a reference material under saturated conditions. Suction effects are incorporated via an intergranular contact force based on the Hill contact model, which considers matric suction magnitude, particle radius, and interparticle spacing. Numerical results demonstrate that suction can be realistically represented by an adhesion force at particle contacts. The model is further extended to simulate triaxial tests, examining the evolution of cohesion and internal friction angle with increasing suction. Both parameters exhibit an upward trend with suction, reflecting the influence of capillary forces and suction-induced densification. Finally, a mathematical model using logarithmic functions is developed to describe the evolution of mechanical parameters as a function of suction, yielding high coefficients of determination (R² > 0.95) and providing reliable predictive capabilities.