1、翻译部分英文原文Formation of fractured zones in overburden due to longwall miningV. PalchikDepartment of Geological and Environmental Sciences,Ben-Gurion University of the Negev,P.O. Box. 653, 84105 Beer-Sheva,IsraelAbstractThe fractured zones caused by mining were studied in the overburden of the Torezko-S
2、nezhnyanskaya area, Ukraine, through the change in natural gas emission from these zones during longwall coal excavation. Zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings. The maxi
3、mum heights of the zone of interconnected fractures and separate horizontal fractures may reach 1941 and 5392 times the thickness of the coal seam respectively. It was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam
4、 increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof. It is shown that the growth of the zone of interconnected fractures occurred during 1739 days at an average rate of 0.941.97 m day)1 and it was accompanied by increasing meth
5、ane emission from overburden. Observation shows that the formation of separate horizontal fractures began only 1149.5 days after the height of the zone of interconnected fractures reached its maximum value. Formation of separate horizontal fractures in overburden over the longwall excavation occurre
6、d as a stepped process from lower to upper sandstone sandy shale layer interfaces in the direction of the ground surface.Keywords:Fractured zones;Longwall coal mining; Interconnected fractures ; Natural gasemission1 IntroductionMany investigators (Turchaninov and others 1977; Karmis and others 1983;
7、 Kratzsch 1983; Hasenfus and others 1988; Palchik 1989; Whittaker and Reddish 1989; Bai and Elsworth 1990; Peng 1992; Kendorski 1993; Chekan and Listak 1993) have found that there are three distinct zones (caved zone, fracture zone and continuous deformation zone) of movement in the overburden rock
8、mass above longwall coal mines (Fig. 1). Turchaninov and others (1977), Peng (1992), and Chekan and Listak (1993) have suggested that the caved zone is highly rubbleised, and extends upwards three to six times the underlying coal seam thickness. In this zone, the overburden rock layers fall to the m
9、ine floor and are broken into irregular shapes of various sizes. Palchik (2002a) has found that the height of the caved zone could reach 4 to 11 times the thickness of the underlying coal seam where overburden rocks are weak and porous. Kratzsch (1983) and Karmis and others (1983) have indicated tha
10、t the height of the caved zone can be 12 times the underlying coal seam thickness.Above the caved zone is the fracture zone which can be divided into three parts: rock blocks, through-going vertical fractures, and horizontal fractures caused by bedding layer separation (Fig. 1). In the lower part of
11、 the fracture zone, rock layers are broken into blocks by vertical fractures and horizontal fractures due to bed separation. The adjacent blocks in each broken rock layer are contacted either fully or partially across the vertical fractures. In the middle part of the fractured zone, there are also h
12、orizontal fractures due to bed separation, whereas the number of through-going vertical fractures is less than in the lower part of the fractured zone. In the upper part of the fractured zone, formation of vertical fractures through thickness of rock layers does not occur and there are only separate
13、 horizontal fractures along weakstrong rock layer interfaces. Palchik (1989) has suggested that the thickness of horizontal fractures at weakstrong rock interfaces in overburden can achieve about 0.4 m. The thickness of thenFig. 1 Zones of overburden movement caused by longwall miningfractured zone
14、varies greatly from 20 to 100 times the seam thickness. The zone above the fractured zone is the continuous deformation zone where there are no major fractures. The extent of the zones of rock movement over longwall mining may vary significantly.In the caved zone, fractures (voids) between irregular
15、 shapes of the collapsed immediate roof are interconnected. Horizontal and vertical through-going fractures in the lower and middle parts of the fractured zone are also interconnected. Therefore, the combined thickness of the caved zone, and the lower and middle parts of the fractured zone is the he
16、ight of the zone of interconnected fractures (Fig. 1). Here interconnected fractures form a system of through channels which are connected with mine workings and, therefore, can be used for drainage of methane. Separate fractures (upper part of fractured zone) are also of interest since methane can be produced from them. In the Torezko-Snezhnyanskaya area, Ukraine, Iofis and Palchik (1984), Ayruni and others (1985) and Palchik (1985, 2002b) have sh
