电磁辐射在煤矿冲击地压预测中的应用外文文献翻译

Calculation of Electromagnetic Radiation Criterionfor Rockburst Hazard Forecast in Coal MinesV. FRIDAbstractIntensive micro-fracturing of rock close to mining operations accompanies an increase in the likelihood of rockbursting. This fracturing causes an increase of the electromagnetic radiation (EMR) level by up two orders of magnitude, depending on the mining environment. Several examples of this enhanced EMR are presented in this paper. We first treat the EMR theoretical criterion of rockburst hazard in coal mines and compare it with the empirical criterion of EMR activity that was revealed on the basis of more than 400 dilTerent hazardous and non-hazardous situations in underground coal mines. Only the following parameters are needed to estimate the EMR criterion of rockburst hazard: limiting value of gum volume, mine working width, coal seam thickness, and coal elastic properties.Key words: Rockburst, electromagnetic radiation, fracture, coal mines1. IntroductionThe phenomenon of rockbursting has long been known in mining. The rockburst hazard increases if the load on a given part of a coal seam exceeds some critical level,while the distance to the stress maximum in the zone of influence of a mine working is lower than the critical value (PETUKHOV and LINKOV, 1983). The rockburst hazard is usually determined by some standard geomechanical method, for example, gum volume measurement, measurement of hole diameter or number of disks that are created due to core fracturing as a result of drilling in a highly stressed zone, etc. (PETUKHOV, 1972). The method of gum volume measurement is generally used in coal mines of the former USSR. All of these methods are very time-consuming and sometimes dangerous becausedrilling is required. For these reasons, rockburst hazard forecasting at a mineworking face must be made short-term and safe. Geophysical methods can help toreduce the risks (FALLON et al., 1997).As noted by LOCKNER (1993, 1996), there is a strong parallel between the well-known Gutenberg-Richter relation for seismic events (from macro (earthquake) to micro (rock burst) and power-law frequency magnitude relationship for acoustic emission (AE) events. This analogy suggests that micro shocks (high frequency and small magnitude) are precursors of macro failure (large magnitude and small frequency) and is the theoretical basis for rockburst forecasting by the AE method (KuKSENKO et al., 1982; MANSUROV, 1994). The EMR frequency range is close enough to the AE band. Therefore, both types of emissions are associated with rock fracture YAMADA et Cll., 1989; OKEEFE and THIEL, 1995; RABINOVITCH et Cll., 1995.Hence, it would be correct to assume that electromagnetic radiation (EMR) could beuseful for rockburst hazard forecasting along with AE. Moreover, being non-contact, the EMR method has advantages over AE. For example, when a rapid and comprehensive prognosis of a short-term mine working region (for example, in a drift face) is needed, the roughness of the mine walls becomes a marked problem for the AE method for rapid data acquisition due to inferior contact between the AE transducer and the mine wall.Numerous investigations have examined different aspects of the EMR (CRESS et Cll., 1987; FUJINAWA et Cll., 1992; NITSAN, 1977; OGAWA et Cll., 1985; WARWICK et al., 1982; YAMADA et al., 1989; YOSHINO et al., 1993). The EMR amplitude is a function of the crack area (RABINOVITCH et al., 1998, 1999). Moreover, an increase of elasticity, strength, and loading rate enhances the EMR amplitude (GoLD et al., 1975; NITSAN, 1977; KHATIASHVILI, 1984; FRID et Cll., 1999).Since the eighties, the interest in EMR has increased in connection with the problem of rockburst forecasting. KHATIASHVILLI et al. (1984) carried out an investigation of EMR in the Tkibulli deep shaft (Georgia) prior to an earthquake of 5.4 magnitude. The registration point (at the shaft position) was located 250 km from the earthquake epicenter. Prior to the earthquake itself, an increase of intensity of the lower part of the spectrum (1100 kHz) and a corresponding decrease of intensity of higher frequencies (100-1000 kHz) were observed. An increase of the number and the sizes of cracks during the earthquake approach could, perhaps, explain this phenomenon. NESBITT and AUSTIN (1988) registered EMR in a gold mine (2.5 km depth). An EMR signal (1.2 mA/m amplitude) was generated seconds prior to the micro-seismic event (magnitude of -0.4). Registra-tion of EMR activity in Ural bauxite mines showed (ScITOVICH and LAZAREVICH, 1985) that its values sharply increased with rockburst hazard increase. Analogous works in Norilsk polymetal deposit (Krasnoyarsk region) revealed an increase of EMR amplitude (up to 150-200 mV/m) and activity in the rockburst hazardous zones (REDSKIN et al., 1985). MARKOV and IPATOV(1986) investigated EMR activity changes in an apatite underground mine (Khibin deposit, Kola peninsula) and ascertained that EMR amplitude in rockburst hazardous zones was in therange of 8-25 mV/m and EMR activity here was significantly higher than the regular noise level. This very limited overview demonstrates that the EMR is a multi-scale phenomenon that is currently investigated in laboratories and in .situ (before earthquake and rockburst). However, all EMR mine investigations have usually been empirical, and the degree of their theoretical generalization is not enough to be useful for rockburst forecasting. This paper first considers a development of the theoretical EMR criterion for rockburst forecasting.2. Comparison of EMR and Gum Methods The promotion of a new method for rockburst forecasting is a very responsible undertaking. Hence, the new method must be comprehensively compared with the method which is currently being used. In this section of the paper we consider the methodological foundation of the gum method that has been used for rockburst forecasting before discussing EMR and the EMR methodology. Finally, several examples of EMR and gum investigations are presented.2.1. Methodology of Gum MeasurementDrilling of a highly stressed coal seam leads to an intensive fracturing process in the zone, influenced by the drill hole. The volume of this highly cracked zone depends on the hole diameter, the drilling rate and, especially, the stress level. Hence, if the first two parameters remain invariant for a given coal seam, the stress value in the coal seam (Fig. 1) is responsible for the volume of drilled coal rubble that is recovered from the hole (i.e., from the highly stressed zone drilled by the hole). If the drilling is dry, the drilled coal rubble is calledgum. The non-dimensional diameter，of the highly stressed zone (ratio of the non-elastic deformation zone, diameter D, to the hole diameter d=0.043 m, Fig. 2) can be calculated from the following formula (PETUKHOV, 1972):where n,. is the coefficient of coal loosening on borehole wall that is generally equal to 1.3-1.4, Mo is the gum volume of a borehole (MD=d2/4A, A is the borehole length), and M,S. is the gum volume induced by drilling in a stressed zone) TUKHOv et al., 1976). The vertical stress in the coal seam can be determined as follows (PETUKHOv et al., 1976)where is the coal shear strength. Forecast boreholes are usually drilled in intervals (the length of each interval is 1 m). Hence, if we determine the gum volume for each meter of the hole, we can predict the vertical stress distribution in the coal seam near the mine working face.where k is the coal shear strength. Forecast boreholes are usually drilled in intervals (the length of each interval is 1 m). Hence, if we determine the gum volume for each meter of the hole, we can predict the vertical stress distribution in the coal seam near the mine working face.After the drilling of each interval, the gum volume is measured and if it exceeds a definite limiting value (experience at the mining works in North Kuzbass shows that the limiting values are 5 to 8 liters per meter at the fourth and the seventh drilling meter from the drift face, respectively (Table 1), drilling is stopped, and that part of the mine working, is considered rockburst hazardous.2.2. EMR Methodology for Mine MeasurementFigure 3 explains the EMR activity definition. The EMR activity is defined by the number of intersections of the EMR voltage signal (per unit time) with a given volt 100 age level (of a special counter). The EMR activity was measured by a resonance 士1 kHz antenna. Our preliminary mine estimation of electromagnetic patibility conditions showed that the given resonance frequency would allow com-us to accurately extract the useful signal from the industrial background noise.Table 1 Calculation of rockburst hazardous zone parameteFigure 1The vertical stress distribution in the zone of influence of the mine working (all parameters are discussed in the text). Figure 2The zone of non-elastic deformation excited by drilling in the high stressed zone (b is the non-dimensioned diameter of this zone:the ratio of the non-elastic deformation zone diameter n to the hole diameter d=0.043 m)Figure 3The EMR signal that intersects counter voltage level.电磁辐射在煤矿冲击地压预测中的应用韦.弗瑞德摘要采矿活动引起的强烈岩石破碎导致冲击矿压发生的可能性增加。这些采矿环境导致的岩石破碎引起电磁放射(EMR)的水平增加。本文阐述了电磁辐射规律显现的几个例子。我们首先对煤矿在开采期基于400多个采动和非采动环境下矿压显现状况引起的电磁辐射显现现象作了统计。其中只需以下参数来对矿压显现导致的电磁辐射作评价：声发射、工作面长度、煤厚、煤层硬度关键词： 冲击矿压 电磁辐射 破碎 煤矿1.简介人们在采矿方面认识冲击矿压现象已经很久了。在部分煤体上的负荷超过一定的水平，冲击矿压发生的可能性就大大增加(PETUKHOV和LINKOV, 1983)。对于冲击矿压发生的预测常常考虑地质因素：生发射的测量、裂隙大小的测量、高应力区域开采导致的岩石破碎度等(PETUKHOV, 1972)。在应用方面，声发射法经常用于前苏联的煤矿。所有的这些方法都非常耗时而且有时很危险，因为需要在开采区域打钻孔，这将导致岩石的应力释放。因为这些原因，工作面冲击矿压危险性预测必须耗时少并且安全。地质方法可以并不能帮助降低这些工作的风险(FALLON等, 1997)。据LOCKNER (1993, 1996)记载, 因为地震原因，著名的古登宝界面和理查德界面有很大的平行面而且有巨大能量的声发射。这个相似点意味着微震 (高频率、小振幅) 是大震 (大振幅、小频率) 的前兆，并且意味着这是声发射法预测冲击矿压的理论基础 (KuKSENKO等，1982; MANSUROV, 1994)。电磁辐射的频率范围与声发射的关系极为密切。因此，两种类型的辐射与岩石破碎有关(YAMADA等, 1989; OKEEFE和THIEL, 1995; RABINOVITCH 等, 1995) 。因此,电磁辐射可以和声发射一起应用于冲击矿压预测。而且，遥控操作使电磁辐射法比声发射法占优势。 举例来说，如果在一个快速推进的工作区域 ( 例如,在一个无人工作面) 矿井巷道的粗糙影响声发射的传输和声发射所需要的各种精确数据构成了矛盾。很多的研究成果已经测试了电磁辐射的不同方面的性能(CRESS等., 1987; FUJINAWA 等., 1992; NITSAN, 1977; OGAWA 等, 1985; WARWICK等, 1982; YAMADA , 1989; YOSHINO , 1993) 。电磁辐射振幅是裂隙区域运动的一个函数(RABINOVITCH et al., 1998, 1999) 。而且，弹力，压力以及它们作用的频率增加会增大电磁辐射的振幅 (GoLD, 1975; NITSAN, 1977; KHATIASHVILI, 1984; FRID, 1999) 。自80年代以来, 对电磁辐射预测冲击矿压问题的研究热度一直在增加。KHATIASHVILLI . (1984)做了一个在深井下预测出5.4级地震的研究。他在井底的观测点距离震源足足有250千米。伴随地震的发生，1-100千赫的低频波急剧增加，而100-1000千赫的高频波在减少。在地震过程种岩石破碎的数量和大小可以，或者大概可以解释这些现象。NESBITT 和 AUSTIN（1988）再次在地表2.5千米下的一个金矿对电磁辐射作了研究。有记载一次微震前一串电磁辐射信号提前发射出来(ScITOVICH 和 LAZAREVICH,1985)。研究还发现乌拉山脉的铁矾土矿的电磁辐射活动显示它的辐射程度迅速地以冲击地压增加而增加(REDSKIN 等, 1985)。类似的情况也在多金属沉淀地层发生，电磁辐射随着岩块破断产生了巨大能量。MARKOV 和IPATOV(1986)在井工矿调查一个磷灰石的电磁辐射活动变化是，确定岩石破断导致的电磁辐射范围在 8-25 mV/ m之间，而且电磁辐射活动在这里也比一般辐射要强。这个非常有限的观点表示，电磁辐射现在是一种普遍在实验室和现场(在地震和冲击矿压之前)被研究的现象。然而, 所有的关于电磁辐射的研究通常是基于经验的，而且理论上的不足对冲击矿压预测是有限的。本文首次拓展基于电磁辐射理论的冲击矿压预测标准。2. 电磁辐射和声发射方法的比较为冲击矿压预测的方法升级是一个非常有意义的事业。因此，新的方法一定要在各个方面与现在目前使用的方法进行比较。在论文的这一部分中我们在讨论电磁辐射法和电磁辐射应用之前，首先讨论目前使用的声发射法，最后将列举电磁辐射和声发射法应用的一些例子。2.1声发射法对高应力煤层打钻的过程导致了一个受钻孔影响的岩石破碎过程。这个高度破碎区域的体积受钻孔直径，打钻速度，尤其是应力大小的影响。 因此，如果前面两个叁数在给定的开采煤层中保持不变，如图1 压力值会对声发射大小有影响。如果干法打钻, 被打的煤岩被叫做 “箱体”(PETUKHOV, 1972)。高应力下的钻孔直径， (强力毁坏区域的直径D,洞直径 d=0.043 m (见图2) 可以由下式求得：其中nr是煤的松散系数，大致为1.3-1.4。Mo是钻孔的声发射值。（TUKHOv et al, 1976). Ms是在高应力区域打钻时的声发射值，煤层应力可由下式确定(PETUKHO等,1976)： 其中k*为作用在煤壁上的剪切力。常常把探测钻孔间隔打(间隔距离1 m)。因此，如果我们为声发射探测每公尺布置一个钻孔,我们能预测工作面煤壁的垂直压力分配。在每打钻之后，就获得一次声发射值，而且到达一定值就停止钻孔。试验工作面被衡量为有冲击矿压发生危险。声发射被测得，而且如果它超过明确的极限(在North Kuzbass的采矿经验声发射限值是每公尺 5 到 8 个单位，出现在第四个和第七个钻孔, (见表 1)。2.2 电磁辐射法在矿井中的应用图3 显示了电磁辐射活动规律。电磁辐射活动规律是由给定(用特殊计算器)的电磁辐射电压信号(每隔单位时间发射)决定的。电磁辐射活动规律由一个士1 kHz测量仪器测量。 表1冲击矿压危险区叁数计算图1工作面矿压影响范围内的垂直应力分布图(所有的叁数在本文中都已定义)图2在高应力区打钻将会对岩体造成塑性破坏 (b 是该区域直径于塑性破坏区直径的比 d=0.043 m)图 3不同电压信号下的电磁辐射显现