Abstract
Coal seam water injection (CSWI) is an effective technology that is widely used for preventing rock burst in coal mines. To deepen the understanding of the mechanism of CSWI to prevent rock burst, new equipment was designed to prepare forcedly saturated coal samples in this study and a series of mechanical experiments was conducted to investigate the mechanical properties, acoustic emission (AE), and energy dissipation characteristics of the coal samples in natural, naturally saturated, and forcedly saturated states. The experimental results show that the forced saturation treatment can significantly improve P-wave velocity and water content of coal samples, as water can penetrate more into micropores and fractures. The forced saturation method also significantly promotes the deformation capacity of the coal sample and reduces the strength by 83.37%. The main reason of the bearing capacity decrease for the forcedly saturated coal samples is plastic yielding rather than brittle crack propagation and slip. The derivative of the volumetric dissipation energy was proposed to evaluate the outburst proneness. The forced saturation method significantly reduces the risk of sudden release of energy and is more effective in preventing rock burst in coal seams than the natural saturation method.
Highlights
Coal mass is a natural multiphase composite material that contains fractures and pores [1]. e mineral composition and microstructure of coal mass can be affected by water soaking which induces natural fracture propagation and softens the organic materials [2], resulting in the degradation in the physical and mechanical properties [3]. erefore, CSWI is widely used in coal mines to prevent rock burst and coal wall caving in the longwall panel [4, 5]
It can be found that the water content for the forcedly saturated coal samples is significantly higher than the natural and naturally saturated coal samples, indicating that the forced saturation treatment can drive water into more micropores and fractures, and is more effective at changing the microstructure of coal samples than the natural saturation method
The increase rate of P-wave velocity is in the range of 3.1%–9.2% for the naturally saturated coal samples, whereas 42.1%–55.6% for the forcedly saturated coal samples. e results suggest that P-wave velocity increases significantly more by the forced saturation treatment than by the natural saturation treatment
Summary
Coal mass is a natural multiphase composite material that contains fractures and pores [1]. e mineral composition and microstructure of coal mass can be affected by water soaking which induces natural fracture propagation and softens the organic materials [2], resulting in the degradation in the physical and mechanical properties [3]. erefore, CSWI is widely used in coal mines to prevent rock burst and coal wall caving in the longwall panel [4, 5]. E mineral composition and microstructure of coal mass can be affected by water soaking which induces natural fracture propagation and softens the organic materials [2], resulting in the degradation in the physical and mechanical properties [3]. By injecting water into the coal pillar, its mechanical behavior and energy release characteristics would be changed to reduce the risk of coal burst. Many studies have been conducted to understand the fundamental mechanical behaviors of water-saturated coal and rock samples. Xiong et al [18] conducted a series of Brazilian tests, uniaxial and triaxial compression tests to investigate the changes of mechanical properties of naturally saturated mudstone samples and suggested that the strength of naturally saturated rock samples was more sensitive to the confining pressure than that of dry samples. Zhou et al [19] studied the influence of water content on mechanical properties of rock treated by both saturation and drying processes and demonstrated that the tensile strengths of the partially water-saturated rock samples with the same moisture content were different during saturation and drying processes due to different
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