The concept of quasi-brittle rock fracture as applied to extraction and processing operations

Abstract

Research objective is to substantiate the method for calculating the value of specific surface energy as the work irreversibly expended on fracture surfaces formation in the course of rock fracture in mining flow processes. Methods of research. The scheme of a uniformly expanded thin brittle plate with an embedded crack perpendicular to the load (Griffith plate) was taken as the basis for analytical calculations. The statement of the problem was based on building the energy balance of the work irreversibly expended on fracture surfaces formation through crack creation and propagation. The general solution analysis revealed that the well-known Griffith formula refers to a particular case of a perfectly brittle material fracture, when a sample in the form of a plate has specific dimensions with respect to the length of the embedded crack. Griffith theory postulates the presence of embedded structural cracks in a fractured body and does not explain the mechanism of crack creation and propagation up to the critical value. Therefore, it has not yet found practical application in analytical calculations of mining operations. Results. To extend application of the obtained design dependence of the specific surface energy for the tough fracture of rocks as well, a modified Irwin criterion has been proposed that determines the condition for the local fracture of crack-like flaws in the material’s structure. Therefore, by introducing a new constant in the form of an integrated structural-textural constant of the rock material, it has become possible to obtain the final answer to the question of what the value of specific energy consumption is in the flow processes of rock fracture by tensile cracks propagation. The theoretical novelty of the obtained regularity, along with its clear, understandable physical sense, is represented in the specific energy irreversibly spent for through tensile cracks creation by substantiated introduction of energy efficiency in the course of fracture, which substantially increases the value of the design energy consumption.