Rock bursts induced by thick-hard roof with compound key strata: Mechanisms and technical modes for prevention

Authors

ZHENG Kaige, CCTEG Xi’an Research Institute (Group) Co., Ltd., Xi’an 710077, China; School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, ChinaFollow
YUAN Liang, School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, China
ZHANG Pingsong, School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, China
WANG Lintao, CCTEG Xi’an Research Institute (Group) Co., Ltd., Xi’an 710077, China

Abstract

Objective Thick-hard roofs serve as the key factor inducing disasters such as rock bursts and mining-induced earthquakes in coal mines. These disasters are especially serious in the case of coal seam roofs with compound key strata. Hence, there is an urgent need to reveal the mechanisms behind the rock bursts induced by thick-hard roofs with compound key strata and to develop technical modes for the prevention and control of these rock bursts. Methods Using methods including physical simulation experiments on similar materials and mechanical analysis, this study developed methods for identifying roofs with compound key strata and for non-synergistic breaking of the compound key strata. Furthermore, this study revealed the mechanism behind the rock bursts induced by the roof and selected the optimal technical mode for prevention. [Results and Conclusions] Key findings are as follows: (1) Thick-hard roof with compound key strata exhibited large and small periodic weighting, with acoustic emission frequency and microseismic energy during weighting being 5.3 and 7.3 times those in the absence of weighting. The synergistic breaking of the upper and lower compound key strata led to disturbance superimposition, with superimposed periodic effects and weighing effects at square locations inducting large-scale rock bursts. (2) An identification model of compound key strata based the neutral axis was established, revealing that the prerequisite for the phenomenon that two or more key strata in the thick-hard roof form compound key strata is that the shear stress on the cross-section does not exceed the corresponding shear strength in the beam model. (3) A method for quantitatively determining the distances of the breaking lines under the cantilever-beam and masonry-beam models was developed. Furthermore, three hydraulic fracturing and pressure relief technical modes were proposed: the fracturing of the upper key stratum, the fracturing of the lower key stratum, and the synergistic fracturing of both strata. (4) The results indicate that the fracturing of the lower key stratum primary, despite changing the integrity and strength of the lower key stratum and shortening the step distance in periodic weighting, failed to control the energetic rock bursts caused by the arched shells of the upper key stratum. The fracturing of the upper key stratum, the predominant layer influenced by rock bursts, controlled the loads induced by breaking disturbance in large weighing cycles, weakened the coupling effects between the compound key strata, and greatly reduced the dangerousness of rock bursts. In contrast, the synergistic fracturing of both strata was identified as the optimal mode for pressure relief and rock burst prevention. The results of this study will provide an important basis for the precise prevention and control of areas potentially struck by disasters such as rock bursts induced by thick-hard roofs with compound key strata and mining-induced earthquakes.

Keywords

thick-hard rock layer, rock burst, composite key layer, synergy, staged hydraulic fracturing

DOI

10.12363/issn.1001-1986.23.11.0788

Recommended Citation

ZHENG Kaige, YUAN Liang, ZHANG Pingsong, et al. (2024) "Rock bursts induced by thick-hard roof with compound key strata: Mechanisms and technical modes for prevention," Coal Geology & Exploration: Vol. 52: Iss. 10, Article 3.
DOI: 10.12363/issn.1001-1986.23.11.0788
Available at: https://cge.researchcommons.org/journal/vol52/iss10/3

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