Experimental Research And Application Of Rock Dynamic Mechanical Properties For Coal Mine Deep Part

Coal is the main energy in China. As coal demand and mining intensity increasing, resources in shallow decrease gradually and will be exhaustion someday, then deep mining will be the inevitable trend in coalmine. For the complex "three highs" mechanical environment deep rock mass in, its mechanical responses for excavation disturbance are obviously different with shallow rock mass. When coalmine tends to deep, potential safety hazards increase which becomes a great threat to safe and efficient mining of deep resource, especially fatal accidents occurred in recent years when first entering deep mining. Thus, in order to ensure supply of reserve coal energy in China, it is extremely urgent to carry out basic theory research of deep mining in coalmine.Based on deep mining in Huainan and Huaibei coalmines, sandstone, the most common rock in coalmine roadway, was selected to research. Rock specimens were collected from different covered depths in various coalmines, e.g. Qidong coalmine(-466m), Wolonghu coalmine(-527m) and Zhujixi coalmine(-962m). Basic physical properties were investigated, and scanning electron microscope test (SEM) and X-ray diffraction (XRD) test were also conducted. RMT rock mechanics test system was also adopted to carry out static mechanical tests. The key issue is using variable cross-secion spilt Hopkinson pressure bar (SHPB) apparatus researching dynamic mechanical properitie. Main research contents and results are as follows:(1) Design and manufacture a fixture in grinding short cylinder rock specimens to ensure its parallelism and axial alignment tolerance. Splitting tensile test and uniaxial compression test were conducted by RMT rock mechanics test system to analyze failure modes and characteristics of stress-strain curve.(2) Propagation of elastic stress wave in split Hopkinson pressure bar (SHPB) test was analyzed. And Rectangular wave, trapezoidal wave, and sloping wave were expressed as trapezoidal wave with different rising times to derivate related calculation formulas for stress distribution along loading direction. Several factors affecting time for stress equilibrium and stress uniformity were studied.(3) Uniaxial compressive mechanical performance of coalmine sandstone under impact loads was studied, and time for stress equilibrium and stress uniformity for three kinds of sandstone were also investigated by smoothed test incident wave and theoretical trapezoidal wave with same rising time. Stress equilibrium could achieved before stress peak by variable cross-section incident bar which met conditions in assumption of stress uniformity.(4) Different loading rates were implemented by adjusting impact pressure to investigate the dynamic tensile performance of coalmine sandstone under high strain rate. Four impact pressure,0.3,0.6,0.9and1.2MPa, were loaded in radial direction. Both actual measured waves and strain rate effect were analyzed and tensile stress and strain rate of sandstone under high strain rate were obtained.(5) Energy composition and energy dissipation characteristics of sandstone in SHPB test were investigated. Failure modes, strain rate effect and dynamic tensile stress were analyzed from energy point. And it is found that energy absorbed by rock specimens almost dissipated in damage evolution and deformation failure, and tensile performance of sandstone under dynamic loads was also reflected.(6)14sizes of sieves,0,0.15,0.3,0.6,1.18,2.36,4.75,9.5,13.2,16,19,26.5,31.5and37mm were employed to conduct broken fragments test. Relationship between broken size and absorbed energy was established by broken fragments analyses and energy analyses. According to the self-similarity of broken rock, fractal characteristics of broken fragments were studied by fractal theory.(7) Combined with characteristics of hard rock in different depth coalmine roadway, parameters in blasting design were optimized by medium-length hole differential blasting in different orders and smooth blasting test. By filed test and engineering application, utilization rate of perforation was more than90%, and average footage per month is improved over20%. So the blasting effect is good.