外文翻译-冲击矿压的防治措施

Prevention and forecasting of rock burst hazards in coal mines DOU Lin-ming, LU Cai-ping, MU Zong-long, GAO Ming-shiState Key Laboratory for Coal Resource and Mine Safety, China University of Mining & Technology,Xuzhou, Jiangsu 221008, China Abstract: Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well asthe effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the deformation and failure ofcoal/rock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, whichperfectly predict sudden and delayed rock bursts. Based on electromagnetic emission (EME), acoustic emission (AE) and microseism(MS) effects in the process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identificationof premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classificationfor forecasting rock bursts in space and time was established. 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 layinga theoretical foundation and establishing references for parameters for the weakening control of rock 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, suitable for roadways subject to hazards from rockbursts 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 premonitory; intensity weakening; strong-soft-strong (3S) structure; directional hydraulic fracturing; anti-impact hydraulic prop.1 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 20 m per year) and geological conditions deteriorate,the mechanical environment and basic behaviorin deep-level mining is significantly different from that in shallow mining and shows obvious characteristics of nonlinear dynamic instability13,which may easily lead to an increase in dynamic disa sters,such as rock 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 and even can increase the possibility of other dynamic accidents such as coal and gas outburst, explosions,etc4. Rock burst hazards exist in over 100 coal mines in China, especially in Fushun, Fuxin, Xinwen,Yanzhou, Kairuan, Datong, Xuzhou and Huating. For example, a serious rock burst and gas explosion accident occurred in the Sunjiawan coal mine in Fuxin, Liaoning province on Feb, 14, 2005. After the ML=2.5 rock burst had 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 production of the underground mine had been severely impactedby 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 control, there are still many key issues requiring further research524. 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 structures 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 sand-stone roofs overlying coal seams is the one of major factors affecting rock bursts. Under conditions of“two-hard” (hard roof and floor), the strength and thickness of the coal 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 effects 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 rocksamples, 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 Fig. 1. Additionally, the index of bursting energy decreases gradually, followed by an increase in the proportion of coal components in compound coal-rock. In contrast, the index of elastic energy increases gradually as the proportion of coal components increases, i.e., the higher the coal height in the compound coal-rock, the larger the index of elastic energy. The larger the hardness of the roof, the higher the degree of stress concentration and vertical stress around the working face. Fig. 2 shows the simulated distribution of vertical stress around a workface when the mining depth is 700 m, the thickness of the roof 6, 20 and 10 m, the bulk modulus 16, 27 and 16 Gpa and 4, 3 and 4 GPa, respectively. As shown in the figure, the vertical stress in the coal-rock mass is much higher under conditions of hard roof than under soft roof conditions. The difference in maximum vertical stress under the two conditions is nearly 44 MPa. The maximum vertical stress in soft roofs decreases approximately 45%. The concentration of local stress appears in the goaf roof near the coal mass side under hard roof conditions.In addition, the variations of hardness and thickness of coal seams also have a large effect on vertical stress distribution of a coal-rock mass under the “twohard” condition, as seen in Fig. 3. The vertical stress in the coal body decreases, with a decrease in the hardness of coal seams, with the difference between hard and soft coal conditions approaching 44.8 MPa. The maximum vertical stress decreases as the thickness of the coal seam increases. From the data of our numerical simulation, a regression analysis shows that the relationship between the maximum vertical stress F and the thickness of coal seam h can be expressed as a quadratic function, i.e., F = ah2 bh + c .Therefore, in the system of “roof-coal seam-floor”,the smaller the thickness of the coal seam, the larger the maximum vertical stress of the coal body. In other words, the smaller the proportion of the coal seam thickness, the easier a rock burst can be induced under the “two-hard” condition.Fig. 3 Relationship between vertical stress distribution on the coal mass side and stiffness of the coal seam3 Technique of multi-parameter classificationforecasting of rock bursts3.1 Effects of AE, EME & MS in the deformation and failure of a coal-rock massThe electromagnetic emission (EME), acoustic emission (AE) and microseism (MS) effects in the process of rock burst failures of a compound coal-rock mass were tested in the State Key Laboratory of Coal Resource and Mine Safety, China University of Mining & Technology. For the compound coal-rock samples, the count rates (or pulse numbers) of the AE & EME include both the deformation and failure of roof and coal. When the applied load approaches the ultimate strength of the coal samples, the roof begins to yield and unload. For the roof part, this will not cause a burst failure in the roof because of its high compressive strength and the deformation and failure of the coal mass will result in an elastic resilience of the roof. In the period of deformation resilience, the count rates of the AE & EME signals decrease. Meanwhile, before the burst failure of the coal mass,much energy is released because the roof starts tounload and springs back, which will accelerate the deformation and failure of the coal mass and the count rates of the AE & EME signals will reach their maximum values. Therefore, the rules for the relations of AE & EME in the premonitory information of rock burst can be written as:t u1 1 u2 2 n = n u + n u (1)t u2 2 n = n u (2)where t n is the time series of the accumulated count rates of the AE & EME signals, 1 u , 2 u are the variations in velocity of the deformation of roof and coal mass, respectively, u1 n , u2 n are the parameters which are closely correlated with the brittleness and UCS of roof and coal body, respectively. Fig. 4 shows the distribution of the count rates (or pulse numbers) of the AE & EME signals by the deformation and failure of the compound samples. As shown in Fig. 4, the count rates of AE and pulse numbers of EME have distinct, two-stage failure features in the process of repeated loading and unloading until impact rock burst failure occurs. The count rates or pulse numbers of AE & EME reach their extreme points before the burst failure of the Fig.3 Time series of AE & EME signalssamples, after which the intensity of the signals decreases suddenly. The signals in the second stage are mainly the results of the deformation and failure in the post-peak phase, with poor and steady signals.As a consequence of these results, the risk of rock bursts in mining and extraction processes of working faces can be monitored and predicted in real-time, Fig. 4 Time series of AE & EME signalsaccording to the multi-parameter premonitory features of AE & EME in the process of burst failures in the compound coal-rock.3.2 Technique of classification forecasting of rock burstsBased on a theoretical analysis, laboratory testing and extensive field trials, the zero, weak, middle and strong risk of rock bursts can be classified quantitatively by a risk index of rock bursts26. According to the various danger levels of rock bursts, correspondingly controlling measures can be taken, as shown inTable 1.For mines and mining districts with a danger of rock bursts, the geology and mining conditions are, in first instance, analyzed by a comprehensive index method and then the danger zone of rock bursts and key monitoring regions are marked off. Thus early rock burst forecasting can be achieved. Based on early forecasting, microseismic monitoring is used for regional monitoring in real-time. For regions with abnormal microseismicity, an electromagnetic emission (EME) method is adopted for further local monitoring. Again, a drilling method can be used for forecasting and effort verification in dangerous local regions. Therefore, the danger level of rock bursts can be determined comprehensively by this classification forecasting technique, where dangerous areas and spots can be controlled using intensity weakening technology.Fig. 5 shows the method of classification forecasts of rock bursts and steps of implementation during field practice. Fig. 5 Method of classification forecasting rock burst and steps of implementation 4 Strong-soft-strong structure effort of rock surrounding roadwaysThe stress within a rock mass surrounding a roadway will be redistributed by the excavation of the roadway. When the superimposition of an in situ stress field and the stress shockwave from the external hypocenter exceeds the limited bearing capacity of the rock surrounding the roadway, the state of balance of the rock mass is broken and the surrounding rock will suffer transient fracturing or cumulative damage from the iterative effort of tension and compression of the stress wave. On the other hand, although the shockwave from the external hypocenter is, at times, not strong enough, rock burst hazards continue to exist if the superimposed stress field exceeds the limited bearing capacity of the rock surrounding the roadway. Therefore, the transmission and disturbance of shockwaves induced by underground mining is a key factor which may be related to impending rock burst hazards in roadways; that is to say, as long as the total superimposed stress intensity is beyond the utmost carrying capacity of the roadway supporting system, rock bursts may happen around the roadway. Based on the disturbance of external shockwaves, a strong-soft-strong structure model for controlling rock surrounding roadways is established. In the strong-soft-strong structure model shown in Fig. 7, the relative, intact status of the external strong structure, causes the attenuation index of the seismic waves to be relatively small. When the seismic waves are transmitted in this structure, there is no significant attenuation of the seismic energy and only a small part of the energy is absorbed. Therefore, the external strong structure is presented as a weak characteristic in its ability to dissipate energy. Because of its poor integrity, continuity and high porosity, the seismic waves can be scattered and absorbed largely in the middle soft structure. Therefore, the middle soft structure is presented as a strong characteristic in its ability of energy dissipation. The stronger the characteristic, the more favorable the protective effect on the surrounding rock. Because of the compact and intact status of internally strong structures, the entire structure just moves following the distortion of the middle soft structure and its own deformation is relatively small. For the capacity of limited energy dissipation, the strong internal structure is also presented as a weak characteristic of energy consumption. Hence, from the point of energy dissipation of shockwaves, a strong-soft-strong structure can be presented as a soft-strong-soft characteristic.Fig. 7 Strong-soft-strong structure model for controlling surrounding roadwaysTherefore, the prevention of rock bursts in roadwayscan be achieved by reducing the external load of the seismic source, by properly setting a soft structure, by improving support reinforcements and by other measures.5 ConclusionsWe have investigated the tendency for rock bursts in compound coal-rock samples and a multi-parameter identification of premonitory technology that mainly depends on MS, EME and AE was formed. Thus a system of classification forecasting rock bursts in space and time was established. As well, we established the intensity weakening theory for rock bursts and a strong-soft-strong structural impact model of controlling rock surrounding roadways, which lays a solid theoretical foundation for the weakening control of rock bursts. In addition, an active control technique based largely on directional hydraulic fracturing and deep hole relieve shots incoal seams and rock has been formed. An anti-impact hydraulic prop, suitable for roadways, subject to rock burst hazards, has been also developed. So far, these research results have been widely used in more than ten burst-prone mining areas, specifically in mines such as the Sanhejian coal mine in Xuzhou, the Jisan coal mine in Yanhzou, the Muchengjian coal mine in Beijing, the Huating and Yanbei coal mines in Gansu and others, where practical and effective results have been obtained.中文译文 冲击矿压的防治措施摘要： 岩爆意味煤矿地层的极端行为，严重威胁着矿工的生命安全，以及包括简矿工的有效性和效率。在我们的研究，为的变形和破坏的弹塑脆性模型煤/岩成立通过理论分析，实验室试验和现场测试，模拟和其他手段。预测和延迟岩石突然爆裂。基于电磁辐射（EME），声发射（AE）和微震（MS）的效果在变形过程，直到从影响煤岩组合样本，多参数识别问题的前兆技术破裂形成，主要取决于以下三种形式的排放。因此我们已经提出了强度弱化控制对周围岩巷道岩石撞击爆裂和强大的软强（3）的结构模型理论，在基于客观的理论基础和建立的岩石破裂削弱控制参数的引用。为了预防的目的，定向水力压裂关键技术参数显示。根据这些结果，以及从深洞控制在煤层和岩石，爆破的综合防治技术，建立和抗冲击液压支柱，从岩爆巷道受危害还制定了合适的。这些技术已被广泛使用于中国大多数煤矿，受这些危害，并已取得了显着的经济和社会利益.关键词：岩石破裂;弹塑脆性模型;多参数前兆，强度减弱;强软强的结构;定向水力压裂;抗冲击液压支柱。 1简介煤炭资源是中国的能源和95的煤源产生主要来自于地下的地雷。随着开采深度的增加（每年约20米）和恶化，力学环境地质条件和基本行为。在深层次的挖掘是显着的差别，显示了浅层开采和非线性动力学不稳定显着的特征1-3，这很容易导致在动态岩爆等，增加了屋顶和大面积塌陷在地雷构成严重威胁的煤炭生产安全的其他问题。岩石爆破是一个典型的动态危害煤矿，这是在一个突然的，快速和暴力的方式排放在煤岩体弹性能量，甚至可以增加，如煤和天然气的其他动态意外造成的可能性突出，爆炸等4。岩爆的危险存在于中国100多个煤矿，特别是在抚顺，阜新，新汶，兖州，开滦，大同，徐州，华亭。例如，一个严重的冲击地压和瓦斯爆炸事故发生在阜新孙家湾煤矿，辽宁2月14日，2005年省。之后的ML = 2.5岩爆的发生，大量的气体排放量，然后引发了严重的瓦斯爆炸和多人受伤，并造成生命损失。因此，安全和高效的矿井生产受到严重影响 由岩石burst.The岩爆机制是一个相当复杂的问题。尽管还有许多重要的研究已经进行了世界各地，从岩爆 岩爆机理研究和灾害预测控制，但仍有许多需要进一步研究的关键问题5-24。我们的研究主要是提出关于预防和在XX大学进行的岩爆防治研究的最新进展。 2. 混合煤岩冲击倾向性从顶板和以前的岩爆楼结构的分析，似乎有相当数量的扫射下岩石坚硬顶板和地板的结构条件发生。特别是硬厚砂，石屋顶上覆煤层是影响岩爆的主要因素之一。根据条件，硬金（坚硬顶板，地板），强度和煤层厚度也有过了煤岩体开挖对二次应力分布有一定影响。因此，对岩爆复方煤岩样品在系统的趋势，煤层层，非盟，以及对岩石的强度和发生爆裂煤层厚度影响的研究，将大大有利于预防和岩爆灾害防治。从混合煤岩样品实验室研究，我们的结果表明，在较高的复合煤顶板组成比例，较高的弹性和破损程度和更大的岩爆倾向模量和无侧限抗压强度（无侧限抗压强度）的样品，如