Abstract
In this study, a 3D simple shear model using DEM is built based on the boundary condition of an NGI-type bidirectional simple shear apparatus. Stack of rings used as lateral constraints in a bidirectional simple shear test is modelled by layers of clumps which is possible to be moved by particles; different contact types and parameters are used to model the sand-loading caps, sand-latex membrane, and sand-sand contacts. A simple shear test using the bidirectional simple shear apparatus is performed for the calibration of the 3D DEM simple shear model. By analyzing the simulation results, the following can be concluded. (1) Rings generated by clumps can provide an accurate boundary condition, effective in computation since no contact force is needed for a clump. (2) In the simulation, the orientation of average contact force changed dramatically during shear. It is in the vertical direction (90°) before shear and changes to 45° at 40% shear strain. No shear band is observed which is consistent with the test, and particles move uniformly. (3) In the simulation, the degree of noncoaxiality is the greatest at the beginning of shear, and it is decreased during shear. However, the degree of noncoaxiality is still large at 20% shear strain where there is a 10° difference between the rotation angle of principal stress and principal strain increment.
Highlights
Introduction eNGI-type simple shear test is mostly used in geotechnical testing of soils, and its one characteristic is using a stack of rings as a lateral constraint for samples. e stack of rings is usually made of frictionless Teflon coated rings, and the rings have different lateral displacements during shear
A 3D simple shear model using discrete element method (DEM) is built based on the boundary condition of an NGI-type bidirectional simple shear apparatus
Stack of rings used as lateral constraints in a bidirectional simple shear test is modelled by layers of clumps which is possible to be moved by particles, and different contact types and parameters are used to model the sand-loading caps, sand-latex membrane, and sand-sand contacts
Summary
Introduction eNGI-type simple shear test is mostly used in geotechnical testing of soils, and its one characteristic is using a stack of rings as a lateral constraint for samples. e stack of rings is usually made of frictionless Teflon coated rings, and the rings have different lateral displacements during shear. NGI-type simple shear test is mostly used in geotechnical testing of soils, and its one characteristic is using a stack of rings as a lateral constraint for samples. When two neighboring rings have a large displacement, the sample will be shear to failure at this plane. The discrete element method (DEM) has been used by researchers to study the mechanical behaviors of granular materials from mesoscope. Different from the finite element method (FEM), DEM can be applied when large displacement occurs in the model. Knowing its advantages in enriching laboratory testing possibilities, many researchers used simulated laboratory tests to study the physical and mechanical behaviors of materials [1, 2]
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