Abstract
Coal mining under hard roofs is jeopardized by rock burst‐induced hazards. In this paper, mechanisms of hard roof rock burst events and key techniques for their prevention are analyzed from the standpoint of energy evolution within geological conditions typical of the hard roofs found in Chinese coal mines. Equations used to calculate the total strain energy densities of the coal‐rock mass and hard roof working face are derived. Moreover, several failure‐causing energy evolution rules are analyzed under various conditions. Various rock roof and coal mass thicknesses and strengths are considered, and a method of preventing hard roof rock burst events is proposed. The results obtained show that rock burst events can be facilitated by high stress concentrations, significant accumulation of strain energy in the coal‐rock mass, and rapid energy release during roof breakage. The above conditions are subdivided into two classes: energy accumulation and energy release. The total strain energies of the coal mass and working faces in the roof are positively correlated with the roof thickness, roof strength, and coal mass strength. The coal mass strength primarily influences the overall accumulation of energy in the working face, and it also has the largest effect on the total energy release (i.e., the earthquake magnitude).
Highlights
Hard roof conditions in Chinese coal mines vary significantly. eir thicknesses can vary from several dozen to several hundred meters. e coal resources under hard roofs occupy about one-third of their total volume
When the area of the suspended roof reaches a certain value, the load carried by hard roof exceeds its ultimate strength, and caving occurs across a large area. is leads to a fast release of the energy accumulated inside the roof and coal seams and causes mining disasters such as rock burst events, severe damage to equipment, and significant casualties and injuries
There are few results on energy evolution during hard roof deformation, energy accumulation laws, hard roof energy conversion and release caused by exposure to breakage, and relationships between rock burst events and coal-rock strength, burial depth, and roof thickness. is paper considers the aforementioned issues in detail and proposes hard roof rock burst control and prevention strategies
Summary
Hard roof conditions in Chinese coal mines vary significantly. eir thicknesses can vary from several dozen to several hundred meters. e coal resources under hard roofs occupy about one-third of their total volume. A hard roof is the rock stratum located above a coal seam or a relatively thin immediate roof It is relatively thick, contains poorly developed joints, and is made up of strong rock with a large bearing capacity. Nawrocki simulated the roof using a shear beam and obtained the stress distribution of the deformed region in the coal seam His results implied that dynamic failure occurs when destabilization in the static equilibrium state exceeds the stress limit of the coal-rock mass, resulting in a rock burst event [5]. There are few results on energy evolution during hard roof deformation, energy accumulation laws, hard roof energy conversion and release caused by exposure to breakage, and relationships between rock burst events and coal-rock strength, burial depth, and roof thickness. There are few results on energy evolution during hard roof deformation, energy accumulation laws, hard roof energy conversion and release caused by exposure to breakage, and relationships between rock burst events and coal-rock strength, burial depth, and roof thickness. is paper considers the aforementioned issues in detail and proposes hard roof rock burst control and prevention strategies
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