1、Prevention and forecasting of rock burst hazards in coal minesAbstract：Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the def
2、ormation and failure of coalrock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, which perfectly predict sudden and delayed rock bursts. Based on electromagnetic emission(EME), acoustic emission (AE) and microseism effects (MS) in t
3、he process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identification of premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classification for forecasting rock bursts in space and time was established.
4、 We have presented the intensity weakening theory for rock bursts and a strong-soft-strong (3S) structural model for controlling the impact on rock surrounding roadways, with the objective of laying a theoretical foundation and establishing references for parameters for the weakening control of rock
5、 bursts. For the purpose of prevention, key technical parameters of directional hydraulic fracturing are revealed. Based on these results, as well as those from deep-hole controlled blasting in coal seams and rock, integrated control techniques were established and anti-impact hydraulic props, suita
6、ble for roadways subject to hazards from rock bursts have also been developed. These technologies have been widely used in most coal mines in China, subject to these hazards and have achieved remarkable economic and social benefits.Keywords：rock bursts; elastic-plastic-brittle model; multi-parameter
7、 premonitory; intensity weakening; strong-soft-strong structure; directional hydraulic fracturing; anti-impact hydraulic prop1 IntroductionCoal resources are the main source of energy in China and 95 of the coal produced comes from underground mines. As the mining depth increases (about 20m per year
8、)and geologica1 conditions deteriorate, the mechanical environment and basic behavior in deep-leve1 mining is significantly different from that in shallow mining and shows obvious characteristics of nonlinear dynamic instability, which may easily lead to an increase in dynamic disasters, such as roc
9、k burst, roofs collapsing over large areas and other problems which pose serious threats to the safety of coal production in mines. The rock burst is one of the typical dynamic hazards in coal mining, which is caused by elastic energy emitted in a sudden, rapid and violent way in a coal-rock mass an
10、d even can increase the possibility of other dynamic accidents such as coal and gas outburst, explosions.etc. Rock burst hazards exist in over 100 coal mines in China, especially in Fushun, Fuxin, Xinwen, Yanzhou, Kailuan, Datong, Xuzhou and Huating. For example, a serious rock burst and gas explosi
11、on accident occurred in the Sunjiawan coal mine in Fuxin Liaoning province on Feb, 14, 2005. After the ML=2.5 rock burst occurred, a large amount of gas was emitted, which then induced a serious gas explosion and resulted in many injuries and loss of life. Thus, the safety and highly efficient produ
12、ction of the underground mine had been severely impacted by the rock burst.The rock burst mechanism is a quite complicated problem. Although much significant research has been carried out around the world, from rock burst mechanism studies to rock burst forecasting and hazard contro1, there are stil
13、l many key issues requiring further research. Our study mainly presents recent progress in research on the prevention and control of rock bursts conducted at the China University of Mining Technology.2 Tendencies in rock burst of compound coal-rock samplesFrom the analysis of roof and floor structur
14、es in previous rock bursts, it appears that a considerable number of rock bursts occur under conditions of hard roof and floor structures. Especially hard thick sandstone roofs overlying coal seams is the one of major factors affecting rock bursts. Under conditions of “two-hard” (hard roof and floor
15、), the strength and thickness of the coa1 seam also has certain effect on the distribution of secondary stress after the excavation of a coal-rock mass. Therefore, the research on the tendency of rock bursts in compound coal-rock samples in the system of “roof-coal seam-floor”, as well as the effect
16、s of the strength and thickness of coal seams on rock burst occurrences, will greatly benefit the prevention and control of rock burst hazards. From the laboratory research on compound coal-rock samples, our results indicate that the higher the proportion of the roof component in the compound coal-rock, the higher the modulus of elasticity and degree of breakage and the greater the tendency of rock bursts and unconfined compressive strength (UCS) in the samples. as seen in F
