Experimental Study on Triaxial Unloading Failure of Deep Composite Coal‐Rock

Abstract

With the deep mining of coal, the phenomenon of high ground stress is more likely to cause dynamic disaster. In view of the above problems, this paper takes the unloading process of coal mining as the background to study the effects of mining rates under different conditions on the mechanical properties and triaxial failure criterion of composite coal-rock, so as to provide a theoretical basis for the prevention and control of dynamic disasters in coal mines. The composite coal-rock models with a composite ratio of 1 : 1 : 1 were tested under different unloading rates or confining pressures. The results show that the triaxial unloading process of coal-rock can be divided into five stages: compaction, single elasticity, elastic-plastic unloading, partial fracture, and complete fracture. In this paper, the failure criterion of composite coal-rock triaxial unloading is derived. The unloading rate has an exponential relationship with the triaxial compressive strength, and the relationship between initial confining pressure and compressive strength is linear. The triaxial compressive strength is determined by both. The peak strains ε of all samples under different unloading conditions were around 0.01. And initial confining pressure had an influence on the strain variation trend during the unloading of composite coal-rock. The higher the initial confining pressure, the greater the elastic modulus. In addition, an increase of initial confining pressure led to the increase of the total energy converted into dissipated part in the process of fracture and caused the obvious increase of the rebound characteristics of the curve. However, the unloading rate had no influence on the strain trend.

Stress-Electromagnetic Radiation (EMR) Numerical Model and EMR Evolution Law of Composite Coal-Rock under Load

“…In addition, comparing the simulation results obtained in Figure with those in other studies, , it can be seen that their results have the same trend. At the same time, the curve in Figure is compared with the results of uniaxial experiments in other studies, ,− and the variation trend is consistent. To sum up, the simulation model established in this study has universality and credibility and can be used to further explore the variation law of EMR in the process of coal-rock loading.…”

“…The coal-rock model is a three-layer structure with a diameter of 50 mm and a height of 100 mm. According to the actual and previous results, ,,,, the materials of the coal-rock model from top to bottom are, respectively, set as “rock-coal-rock” and the volume ratio of each layer is 1:1:1. The outer air is spherical with a radius of 150 mm.…”

“…Coal-rock dynamic disaster is always accompanied by the deformation and failure of coal-rock under load, so the perception of coal-rock stress state will be beneficial to prevent disasters. At present, a large number of scholars in various countries have gradually explained the corresponding relationship between coal-rock stress state and its failure − and further established the mathematical model between external factors and fracture state at the same time . These results have theoretical significance for the prevention of coal and rock dynamic disaster and could further reveal the mechanical process and instability mechanism of composite coal-rock under load.…”

Coupling Mechanism of Dissipated Energy–Infrared Radiation Energy of the Deformation and Fracture of Composite Coal-Rock under Load

“…At present, most of the existing research results in this field are merely on the variation law or coupling relationship of observable physical parameters: Li X. et al . − used numerical simulation to study the coupling mechanism of the temperature, stress, and electromagnetic field of composite coal-rock in the process of loading; verified the simulation conclusion based on experiments; and established the multi-physical field coupling model of composite coal and rock and the triaxial failure criterion under different unloading conditions. Liu X. et al .…”

Investigation on the Properties of Gneiss under Different Ground Stresses

“…Liu [20] explored the fracture morphology caused by rock excavation under high geostress, and revealed the failure mechanism. Li et al [21] performed triaxial unloading tests on coal rocks under high ground stress at different unloading rates. Zhang [22] explored the deformation characteristics of roadway surrounding rocks under high ground stress through theoretical analysis, field test, and laboratory test.…”