SIMULATION OF SAMPLE TESTING UNDER COMPRESSION WITH THE HELP OF FINITE-ELEMENT MODEL OF ROCKS BEING BROKEN

Purpose of the paper is to develop mathematical model describing nature of argillous and salt samples under compression and to make available microdefects using finite-element method. Methods. To simulate behaviour of cylindrical rock samples under axial strain, finite-element model of rocks, being broken, is applied. In terms of the assumed model, components of medium with the disturbed continuity are calculated as those being continuous with anisotropic deformational and strength properties. Failure is considered as strength loss in terms of displacement and tensile on the anisotropy planes of the element. Within each point of the medium (if finite-element method is applied, then each element is meant) the limited number of planes of possible failure with 45 degrees pitch is considered; they are used within each stage to evaluate potential failure resulting from displacement stresses or tensile ones. Coulomb-Mohr criteria as well as tensile strength are applied to determine potential failure on sites. Findings. It has been determined that mathematical modeling enables observing the process of disturbances within the sample. Stress-deformation diagrams, being a result of the modeling, demonstrate features of the sample behaviour during different loading stages (i.e. nonlinear nature up to the peak load; decrease while breaking; residual strength; and hysteresis loops in terms of cyclic loading). It has been proved that if the model parameters are selected adequately, acceptable coincidence of both calculated and laboratory curves describing connections of axial strains and side strains with pressure on the samples of clay, sylvinite, and rock salt can be achieved. Originality. Finite-element has been developed. The model makes it possible to describe processes of strain and failure of rock samples in the context of laboratory tests; moreover, the model differs in the fact that it is added by the description of deformation processes taking place in microfissures and pores. Practical implications. Modeling with the use of finite-element method for rocks under breaking helps reach sufficient coincidence of the calculated diagrams of sample tests with graphs of stresses-deformations connection resulting from the laboratory studies. The obtained positive results confirm applicability of finite-element model of rock deformation and failure in terms of rock pressure problems.