Master of Engineering Science
Civil and Environmental Engineering
In this series of studies, the capability of Discrete Element Method (DEM) to simulate the behavior of granular materials has been examined. In the first study, various boundary conditions are simulated through a series of DEM-based miniature calibration chamber tests to investigate the influence of boundary conditions on cone tip (qc) and sleeve frictional (fs) resistances. The second study focuses on the influence of microparameters such as state, modulus, rolling resistance, inter-particle friction, and probe properties on CPT measurements in a centrifuge setting. DEM has been used in the last study to investigate the instability of granular materials under drained and undrained failure conditions. 3D assemblies of the stacked-ring simple shear device were modeled to simulate monotonic constant volume, constant stress, and drained constant shear stress paths. Overall, DEM can successfully capture the instability and large deformation behavior of granular materials.
Summary for Lay Audience
The mechanical behavior of granular materials is predominantly dominated by the forces transmitted through contacts between grains. Simulation of the distinct behavior of soils using continuum approximations has always faced challenges, specifically in modeling large deformation failures. Discrete Element Method (DEM) with a distinct nature can perfectly capture the behavior of granular systems and assemblies by modeling contacts between rigid spheres or disks. Within the confines of this study, DEM has been used to model the behavior of compressible sandy soils. In the first series of this study, a penetration test commonly known as the Cone Penetration Test (CPT) has been simulated. Despite the versatility and simplicity of this test, the application of CPT in remote areas is expensive and requires extensive knowledge of the effect of various parameters in measurements. For this reason, miniature calibration chamber tests have been proposed in the laboratory settings to replicate the penetration tests in a smaller volume of soils. This has led to significant boundary condition problems in the measurements; therefore, various boundary conditions in a miniature cone penetration test has been simulated to capture the actual penetration resistance representing the free-field condition. To illuminate the governing factors in CPT measurements, a series of sensitivity tests have been carried out to investigate the effect of micro and macro parameters on CPT measurements. In the last series of simulations, Direct simple shear test has been simulated as an invaluable test in replicating the static or dynamic liquefaction behavior of sand. Liquefaction is a catastrophic phenomenon occurring in saturated sandy materials, that leads to loss of strength in the medium with the soil behaving as a liquid. This form of instability in granular soils has been fully investigated in the last chapter to understand the failure mechanism in undrained and drained conditions.
Hashemi, Seyedshayan, "Towards Realistic Simulation of Penetration Tests and Instability Analysis of Sand: A Micromechanical Perspective" (2021). Electronic Thesis and Dissertation Repository. 7691.