Dynamic characteristics of coal specimens with varying static preloading levels under low-frequency disturbance load

Abstract

The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces. This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system, and studied the strength evolutions, surface deformations, acoustic emission (AE) characteristic parameters, and the failure modes of coal specimens with different static preloading levels were studied. The disturbance damage is positively correlated with the coal specimen static preload level. Specifically, the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60% and 70% of the uniaxial compressive strength (UCS) were 2.66 and 3.19 times that of the 50% UCS specimens, respectively. Macroscopically, this behaviour manifested as a decrease in the compressive strength, and the mean strengths of the disturbance-damaged coal specimens with 60% and 70% of UCS static preloading decreased by 8.53% and 9.32%, respectively, compared to those of the specimens under pure static loading. The crack sources, such as the primary fissures, strongly control the dynamic response of the coal specimen. The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.

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