Progressive Damage Process and Failure Characteristics of Coal under Uniaxial Compression with Different Loading Rates

Abstract

To study the effect of loading rate on the progressive damage and failure characteristics of coal, an ultrasonic detector and a camera were used to measure the P-wave velocity and record the failure process of cuboid coal samples in uniaxial compression tests with five loading rates. The mechanical properties, damage process, and failure characteristics of the samples were analysed, and the mechanism of the advancing velocity of the working face in coal failure was discussed. The results show that, as the loading rate increases, the peak strength of the sample generally shows an increasing trend, but the elastic modulus changes irregularly. The sample is more prone to local failure before the peak strength. An increase in the loading rate rapidly promotes damage in the sample and accelerates the transition from internal damage to macroscopic failure, with no obvious effect on the ratio of damage threshold to corresponding peak strength. At low loading rates, the samples mainly experienced static failure; the failure form was spalling, and the failure range was wide. At high loading rates, the samples were prone to dynamic failure in the local area, manifested as the ejection of slabs and debris. A greater loading rate produced smaller and thinner slabs and a greater ejection velocity. Properly increasing the advancing velocity of the working face is conducive to reducing spalling to prevent large-area roof fall, but it may increase the possibility of coal burst in local areas. The results of this study provide a reference for roof control and coal burst disaster prevention on the working face in deep coal mining.

A Study on the Influence of Mining Depth on the Stress Distribution Characteristics of Stope Surrounding Rock

“…Loading Pressure of Overlying Rock and Layout of Measuring Points. The similar materials selected for this similar simulation test include fine sand, gypsum, lime, and water to simulate the rock and coal seams, and the similar material proportioning scheme is determined according to the strength law of the coal body at different mining depths [11]. The joints between adjacent rock layers are simulated by scattering mica powder with uniform thickness.…”

“…As one of the main structural parameters of stope, mining depth directly affects the magnitude of mine pressure. With the increase of mining depth, the probability of coal wall spalling and floor heave increases, and the pressure of deep mine appears violently [8][9][10][11].…”