Abstract
Based on a new elastic clump model, a flexible membrane is proposed for the discrete element numerical simulations of triaxial tests. Conversional triaxial tests of sandstone under the confining pressures of 2 MPa and 8 MPa were carried out, in order to validate the effectiveness of the proposed numerical simulation method. The numerical model is validated by comparing the numerical results with the test results. The deformation and failure process of numerical model is analyzed by stress–strain curves, micro fractures, displacement fields, stress fields and energy fields. The model shows an X-shape shear failure zone, of which the angle is very close to that of the test; the dip angle of most shear fractures is close to the angle of the internal friction; and there is a large amount of slipping frictional heat generated on the failure surface. During the loading process, the stress chain and stress concentration appear in the middle of the model, which lead to displacement zoning in the model. The failure of the model is associated with the growth of the micro tensile- and shear fractures. This study provides an effective tool for the macro–micro investigation of rock failure processes.
Highlights
Based on a new elastic clump model, a flexible membrane is proposed for the discrete element numerical simulations of triaxial tests
Cil and Alshibli proposed a flexible membrane boundary model consisting of spherical elements in P FC3D,the hexagonal element arrangements were adopted for the flexible membrane; the flexible membrane can replicate the confining stress uniformly applied in real triaxial tests and predict the macroscopic stress–strain behavior and deformation characteristics of granular materials, small elements may leak out of the gap between the membrane elements, in particular, when under large compressive s trains[15]
Based on the elastic clump model, we propose a new flexible membrane principle that allows overlapping among elements
Summary
The test sample was Jurassic grey fine sandstone of Majiagou, Zigui County, China. The sample was cylindrical with a diameter of 50 mm and a height of 100 mm. Numerical simulations of triaxial tests The flexible membrane. In real conventional triaxial tests, the confining pressure applied on the membrane is always perpendicular to the surface of the membrane and towards the sample. In order to simulate the effect of the confining pressure, the flexible membrane is decomposed into many quadrilateral regions. The flexible membrane may be deformed during the simulation, the confining force will always perpendicular to the membrane surface, so as to simulate the effect of confining pressure in real experiments. In correspondence to the real experiments, the numerical model is consisted of a top boundary, a top pressure plate, a lateral flexible membrane, an internal sample, a bottom pressure plate and a bottom boundary. The force between the lateral flexible membrane and the pressure plates was neglected in numerical simulations. In the regular packing model, there are analytical solutions between the micro mechanical parameters of the elements and the macro mechanical properties of the model, i.e. the conversion formulas[31]:
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