Geotechnical Engineering

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Browsing Geotechnical Engineering by Author "Agegnehu, Gizaw"

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    A Discrete Element Model for the Numerical Simulation of Granular Geo-Materials
    (Addis Ababa University, 2021-11) Agegnehu, Gizaw; Tensaye, Gebremedhin (PhD)
    This work presents computer simulation tools that use a coupled discrete- nite element methods for the modeling of granular materials. The simulation provides a new insight (perspective) in understanding the behavior of granular media at a microscopic level.It introduces and implements prevailing methods of computer sim- ulation to examine the internal dynamics of granular material that are typically not amenable to direct observations in the laboratory and eld investigations. The sim- ulation techniques are implemented using an object-oriented programming approach via C++ and python in the open-source Linux package YADE. The fundamental formulation of DEM ,FEM and the coupling scheme of discrete- nite element methods is presented. Along with Discrete Element soil sample and packing generation algorithms are discussed. Among the proposed packing algo- rithms, Multi-layer under compaction packing process is adopted since it mimics the natural layer-by-layer depositing process of granular materials . Accordingly, an algorithm is presented and coded in the platform (YADE). Then the generated DE soil sample is used to simulate a series of direct shear tests. The microscopic view of Direct Shear Test (DST) is studied on the shear behavior of dense and loose sand. The output results of the numerical simulation is validated with laboratory DST. The deformation pattern, stress-strain relationship, and change are analyzed.The DEM assemblies with porosity =0.65 (dense sand) shows strain softening and volumetric dilation behavior. While strain hardening and volumetric contraction is observed for the assemblies with porosity =0.8 (loose sand) which is the typical shear behavior of Dense and loose sand in laboratory DST.Furthermore, the deformation pattern observed in the simulation is localized within the shear zone of the sample which is comparable to observations from the laboratory Direct Shear Test. when the shear stress arrives at a steady-state after large shear displacement, the soils inside the shear band reach a critical state while the entire sample doesn't. The critical properties of the sand in DST should be investigated from the shear band instead of the entire sample. This property is di cult to capture in laboratory DST however the simulations allow us to resolve the limitation.Finally, a technical manual for the development process of computer simulation tools to provide an e cient approach for solving coupled discrete- nite geotechnical problems is presented.