Geotechnical Evaluation of the Effects of Contact Parameters on the Mechanical Behaviour of Granular Soil Using the Discrete Element Method (DEM)

In geotechnical engineering, shear strength is a fundamental parameter for the design of structures such as dams, foundations, retaining walls, and tunnels. Traditionally, shear strength, which is a function of the internal friction angle and cohesion, is determined through laboratory and field tests. However, with advances in computing, the Discrete Element Method (DEM) has emerged as an effective alternative for modelling and defining these parameters. This study used DEM to model the shear strength of granular soil. The simulation replicated a cylindrical direct shear box test with a radius of 52 mm and a height of 75 mm, applying normal stresses of 12.5, 25, and 50 kPa. The results were then compared to corresponding laboratory tests. The research distinguished itself by focusing on three critical aspects of DEM modelling. First, it aimed to determine the optimum number of sand particles by examining how particle count interacts with density and shear strength. Second, it explored the influence of shear rate on shear strength parameters. Lastly, the study evaluated the impact of contact friction properties—specifically static friction, rolling friction, and restitution coefficients—on the overall shear behaviour.The findings demonstrate a clear relationship between the tested variables and the internal friction angle. Increasing the shear rate from 0.5 mm/sec to 1 mm/sec and then to 2 mm/sec raised the internal friction angle by 9% and 11%, respectively. Similarly, a rise in the number of particles from 40,000 to 42,500 and then to 45,000 resulted in a 3.2% and 4.67% increase in the internal friction angle, though this was found to affect the accuracy of the results. The study also concluded that optimal shear behaviour in granular soils is achieved with moderate values for static friction (0.5–0.75), rolling friction (0.5–0.6), and restitution (0.05–0.06) coefficients, underscoring the vital importance of accurately calibrating these parameters to reflect real-world conditions.