Characteristics of stress evolution of "roof-coal" structure body lose stability process under force and rock burst preparation is analyzed by comparative test. Catastrophe theory is used to analysis instability mechanism and the multi-field stress control for rock burst prevention is established. It's shown that the rock burst tendency of "roof-coal" structure body is better for dangerous estimate. Initial stress and mining-induced stress superposition is the base of structure instability, the high increment of mining-induced stress induces to rock burst. When the "roof-coal" structure body meet the conditions of K/k1≤ 1 and 2u0K-KS-F/K1 +2u0<0 rock burst occurs. Both the High hydraulic fracturing and the coal stress discharging blasting in deep hole are able to change the state of stress, either makes the concentration stress release or transfer to deep coal seam, damage the conditions of high stress or energy for rock burst, the rock burst is prevented and controlled.

1 Instruction

With increasing mining depth and mining intensity, complex geology and stress environment cause many kinds of dynamic disaster during deep coal seam mining, especially rock burst. By the end of 2011, rock bursts occurred in more than 120 mines in China and caused huge economic losses and casualties. Monitoring and prediction on rock burst has become the prime problem for safety and high efficiency in deep mining (Jiang 2012). From the aspects of strength, stiffness and energy are adopted to study the mechanism and prediction technology by many scholars and some progresses have been achieved, for instance, the coal or rock burst has association with its outburst proneness, which is the most popular index for rock burst prediction and evaluation used all over the world. The coal or rock outburst proneness can be predicted or estimated well in shallow coal mining, while the underestimation often occurs in deep mining, especially there is a thick and strong roof above the coal. As dynamic instability, rock burst is the result of discontinuous displacement for stress or energy discrete transfer in coal and its roof and floor under loading superposed by the in-situ rock stress and mining induced stress. So the rock burst not only depends on coal or rock outburst proneness, but also depends on the coal rock structure, the occurrence characteristics and surrounding rock properties. This is why rock burst often occurs in coal seam with changing thickness and faults. The dynamic instability mechanism of combination of coal rock was studied by the stickslip theory (Qi 1996). The characteristics of roof are important to the rock burst, especially the roof is thick sandstone (Wang 1991;Wan 1999). The difference of outburst proneness between coal and coal-rock combination was studied in numerical simulation and the outburst proneness of coal-rock combination higher than coal (Liu et al., 2004; Li et al., 2005). The outburst proneness have a relationship with its material composition (Pan et al., 2005). The evolution of rock burst tendency and its acoustoelectric effect about coal-rock combination was studied by laboratory tests (Lu et al., 2007). Through the contrast test on coal and coal-rock combination sample in depth, the failure mechanism and mechanical properties were analyzed (Zuo et al., 2011). These researches focused too much on the portfolio ratio and the macro failure process of coal-rock combination, the internal factors which lead to the structure instability were neglected and failed to reveal the law of rock burst evolution, the prediction and prevention on rock burst becomes impossible. From the actual situation of coal occurrence, the roof-coal structure body is established. According to laboratory contrast tests on coal, rock and roof-coal structure body, the evolution characteristic of outburst proneness and the rules of instability were studied. The theory of multi-field stress control for rock burst prevention was advanced, including the regional stress coordination to local stress control, the high hydraulic fracturing and coal stress discharging blasting in deep hole were tested in field, both of the technology are effect.

This content is only available via PDF.
You can access this article if you purchase or spend a download.