1、翻译部分英文原文In situ permeability measurements to establish the influence of slice mining on floor rocks.1. IntroductionBelow PermoCarboniferous coal-bearing formations in coal fields of North China, there is a stratum of Ordovician limestone containing an abundant supply of water, and aquicludes with di
2、fferent thicknesses exist between the coal seams and the Ordovician limestone. Recent laboratory and field investigations show that if there are faults or strata failures induced by mining, water flowing zones might be formed in these aquicludes. If a large amount of Ordovician confined water floods
3、 into the coal mine tunnels and working faces, mines may be threatened. In recent years, water inrushes frequently occurred on various scales in many mines of North China.The results of studies in this field have been offered in publications and may be classified into three aspects.1. Various conclu
4、sions were drawn from examples of water inrushes 1. 2. Using mechanical methods and similarity principles, the influence of mining on floor rocks was analyzed 2 and 3. 3. In situ experiments were performed to estimate the failure state of floor rocks 4. Despite these studies, all the mechanisms of w
5、ater inrushes are not known.At present, slicing methods are widely used to mine thick coal seams. For slice mining, a thick coal seam is divided into several thin seams along planes parallel to the seam (Fig. 1) and longwall face working is used for each slice. Slice mining is characterized by the m
6、ethod of roof control in working faces where metal meshes are suspended between roof and support (Fig. 2). After the first slicing ends, metal meshes are laid on the floor of the slice for the next stage of mining below. As a result, the combination is achieved of the roof of the first slicing being
7、 controlled and the artificial roof of the second being laid. In situ experiments show that the bearing pressure in coal pillars of the face for the first slicing is larger than that for the second and the pressure on supports at the face for the first slicing is smaller than that for the second. Th
8、is is because the roof of the second slice consists of blocks of different sizes and shapes which are formed in the first slicing. Based on these facts, it is presumed that the special roof states of the second slicing may induce a lesser influence on the floor rocks because the main perturbation to
9、 the rock stresses occurs during the first slice. However, relatively little is known about changes of floor permeability in slice mining and few experimental data are available.Fig. 1. Slice mining and the layout of boreholes for injecting water.Fig. 2. The roof control of slice mining.From the poi
10、nt of view of preventing water inrushes, changes of floor permeability associated with the mining should be understood. Therefore, it is necessary that new methods be used to develop understanding of the mechanisms of water inrushes and that in situ data be obtained to evaluate existing ideas for pr
11、eventing water inrushes. Bearing this in mind, we used a method of injecting water into floor strata through boreholes in order to study changes of floor permeability as a result of the slicing process. The site for the field tests is located in the Zhao Gezhuang MineHebei Province, China, where an
12、adverse water inrush from confined water in the Ordovician limestone occurred in 1972.This Note begins with a description of the experimental set-up designed to measure the floor permeability to water. We then present the data obtained in the in situ experiment. The results of the measurements are u
13、sed to try to identify the influence of slice mining on floor permeability and explain the different mechanisms of floor failure in slice mining.2. Testing methodologyThe Zhao Gezhuang mine is situated in the Kaiping downfall formed during the PermoCarboniferous period. The working face used for the
14、 in situ permeability measurements is located at a depth of 1000m, the coal seam is 10m thick and the dip angle is about 26. The roof rocks of the face are composed of claystone and siltstone and the floor rocks consist of siltstone, mudstone and gritstone. The coal seam is about 140m away from the
15、Ordovician limestone in which the pressure of confined water ranged from 7 to 9 MPa. An inclined slicing method was applied and the face was advanced along the strike direction of the coal seam. The coal thickness of each slice remained in the range of 2.02.2m.With the purpose of laying out borehole
16、s used to inject water, a tunnel was excavated in the floor rocks of the face (Fig. 1). Eight boreholes were made in the coal seam dip direction, and all in a vertical section. (This vertical cross section is referred to as the section in the following text). The face was advanced across the section during the process of injecting water. The layout of the eight boreholes in the sect
