Mechanical Properties and Deformation Failure Characteristics of Anthracite Under the Conditions of Loading-Unloading

Based on the conventional triaxial and loading-unloading mechanical experiments, the strength characteristics, the deformation and failure characteristics and shear parameters of the anthracite under two kinds of stress path were analyzed. With the increase of initial confining pressure, anthracite peak strength increase under two kinds of stress path. Compared with the conventional triaxial experiment, internal friction angle increases, the cohesion decreases under loading-unloading conditions; under the same initial confining pressure, the compressive strength is reduced, thus easier to failure. In loading-unloading experiments, unloading confining pressure rate slower, the greater the degree of deformation and failure of coal specimen; the faster the rate of unloading confining pressure, the smaller the coal specimen fracture strength, and the shorter the time required, , the coal specimen more easy to failure. In the process of unloading confining pressure, the deformation modulus of coal increased first and then decreased, the Poisson's ratio continued to increase. Compared with the conventional three axis experiment, under the loading-unloading experimental conditions, the difference deformation modulus E₅₀-E_c and the difference Poisson's ratio μ_c-μ₅₀ have a larger increase, and it demonstrated a greater degree of deformation and failure in loading-unloading experiments.