Large-Scale Discrete Element Modelling of in-situ Direct Shear and Plate Load Tests on Granular Soils

This study unveils a novel and potentially economical particulate discrete element modeling (DEM) technique for large-scale simulation of in-situ direct shear tests (DST) and plate load tests, aimed at accurately determining the shear strength and bearing capacity of granular soil foundations, and exploring the key factors influencing these properties. To overcome the limitations associated with the oversimplification of particle shapes, this work introduces an innovative contact model based on the Hertz contact mechanism that incorporates rolling resistance, enhancing the model's ability to simulate realistic particle interactions. Guided by Prandtl's foundation bearing-capacity theory, the dimensions of the foundation model for the DST and plate load tests were meticulously calculated to reflect realistic conditions. DEM simulations showed the peak friction angle from in-situ DST to be consistently lower than laboratory DST, due to a smaller dilatation angle, while proposed loading methods for plate load tests established linear relationships between the foundation's ultimate bearing capacity and its dimensions, also defining the capacity envelope. Crucially, this study highlights a crucial finding: in-situ direct shear tests (DST) conducted under high normal stress may lead to foundation failure, indicating that excessive normal stress should be avoided to ensure the accuracy of in-situ shear test data and its subsequent applicability in engineering design.