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51.
Summary As part of an effort to understand the mechanics of fine fragment formation in coal, which is important in studies of respirable dust due to mining, fracture toughness measurements and the strain energy density (SED) theory were applied to calculate the crush zone size under a cutting tool in coal. This zone is the major source of fine fragments in the 1 to 10 µm size range. The model used in these calculations is a boundary element program containing a failure criterion based on the SED theory. The boundary element program calculates linear elastic stresses at numerous points in the coal material ahead of a cutting bit. These stresses are then input to a subroutine called critical flaw length and orientation (CFLO) which uses the SED theory to determine the CFLO for a small crack at the boundary element stress computation point. The extent of crushing is based on earlier postulates about the role of inherent flaws in a fragmentation process. To form 1 to 10 µm fragments requires firstly a local stress strong enough to activate flaws with a characteristic length less than 1 to 10 µm and secondly, a flaw density sufficient to provide an average spacing between flaws also on the order of 1 to 10 µm. The locus of active 10 µm flaws represents the maximum possible extent of fine fragmentation in the 10 µm or less size range assuming that a sufficient inherent flaw density exists. The approach offers a first order approximation to the extent of crushing under a tool tip. The size and shape of the crush zone volume is affected by the attack angle and geometry of the tool. 相似文献
52.
Summary This article discusses methods for providing a reliable forecast of the gas-dynamic behaviour of coal seams and adjacent strata. It shows that the ash content of carbonaceous materials determines their sorptive capacity (a universally applicable expression is presented for calculating the methane content of a sample) whilst the rate of methane desorption is a function of the degree of geological disturbance, i.e. the number and distribution of the macropores and fractures in the sample. This effect becomes less important as the sample ash content increases and effectively disappears above a certain value for high permeability materials.The quantity sorption-kinetic characteristic is shown to be a reliable means for quantifying methane emission behaviour. Large variations in coal sorption-kinetic characteristics are shown to occur over short distances as the geological structure of the seam changes, both vertically and horizontally. Consequently, sorption-kinetic characteristics may be used to predict the general level of methane emission from the seam and to quantify the risk of outburst inherent in disturbed areas of coal seams. 相似文献
53.
David A. Newman 《Geotechnical and Geological Engineering》1989,7(2):163-170
Summary An indication of the complete stress-strain behaviour of coal was obtained through instrumenting a headgate yield pillar and monitoring the changes in vertical and horizontal pillar stress, pillar strain, and roof-floor convergence as a function of time and distance from the moving longwall face. A semiautomated monitoring program was conducted over a 5 month period as the longwall face advanced toward and eventually passed the instrumented pillar. The development of a confined core and yield zone within the pillar was confirmed by the vertical and horizontal stress changes. Thein situ pre-failure (208 to 661 MPa) and post-failure moduli (55 to 208 MPa) of the coal were determined from the change in pillar stress versus pillar strain. Thein situ moduli are an order of magnitude lower than the 3450 MPa, commonly assumed for coal. 相似文献
54.
The Tertiary sedimentary sequence in the Lusatian Brown Coal District is the result of several transgressive pulses with intercalated regressive phases. Regression repeatedly resulted in the formation of large littoral bogs at the transition between brackish and terrestrial palaeoenvironments. In the lithofacies changes of the Lower-Middle Miocene strata (high energy sands, low energy intertidal silts, paralic peats) long-term changes as well as short-term oscillations of sea level are recorded. The rise of sea level in the upper Lower Miocene (Hemmoorian transgression) is proved in numerous localities of the investigation area. After a regression phase with major peat formation events around the Lower-Middle Miocene boundary, a renewed sea-level rise resulted in the widest extension of marine-brackish beds over pre-Tertiary basement in the south of the region (higher Reinbekian transgression, Middle Miocene). Very differentiated, fine-scaled, probably sea-level induced coastline oscillations could probably be traced even into the coal seams by the recognition of successive bogfacial types possibly showing a groundwater level change in the ancient peat bog (change of topogeneous and ombrogeneous bog types). A biostratigraphic calibration of the decalcified Lower-Middle Miocene sequence with its alternating transgressive and regressive trends to the fully marine sediments of the basinal centre, which are dated by calcareous microfossils, is possible by means of dinoflagellate cysts and pollen and spores.
Correspondence to: C. Strauss 相似文献
55.
W. C. Rember T. W. Erdman M. L. Hoffmann V. E. Chamberlain K. F. Sprenke 《Environmental Geology》1993,22(3):242-245
For over a century Medicine Lake in northern Idaho has received heavy-metal-laden tailings from the Coeur d'Alene mining district. Establishing the depositional chronology of the lake bottom sediments provides information on the source and rate of deposition of the tailings. Cesium-137, an isotope produced in the atmosphere by nuclear bomb tests, was virtually absent in the environment prior to 1951, but reached its apex in 1964. Our analysis of cesium-137 in the sediments of Medicine Lake revealed that 14 cm of fine-grained tailings were deposited in the lake from 1951 to 1964 and tailing deposition downstream was greatly reduced by the installation of tailings dams in the district in 1968. Cesium-137 analysis is accomplished by a fairly simple gamma-ray counting technique and should be a valuable tool for analyzing sedimentation in any lacustrine environment that was active during the 1950s and 1960s. 相似文献
56.
57.
James C. Hower John K. Hiett Garry D. Wild Cortland F. Eble 《Natural Resources Research》1994,3(3):216-236
The Eastern Kentucky coal field, along with adjacent portions of Virginia and southern West Virginia, is part of the greatest production concentration of high-heating-value, low-sulfur coal in the United States, accounting for over 27% of the 1993 U.S. production of coal of all ranks. Eastern Kentucky's production is spread among many coal beds but is particularly concentrated in a limited number of highquality coals, notably the Pond Creek coal bed and its correlatives, and the Fire Clay coal bed and its correlatives. Both coals are relatively low ash and low sulfur through the areas of the heaviest concentration of mining activity. We discuss production trends, resources, and the quality of in-place and clean coal for those and other major coals in the region. 相似文献
58.
三山岛金矿F3断裂带的水文地质工程地质特征及灾害防治 总被引:2,自引:0,他引:2
本文对三山岛金矿F3断裂带的构造、岩性和水动力学特征进行了研究,对矿坑开挖中的突水和坑道碎屑流的成因做了探讨,并在水文地质结构、水化学、水同位素及水文地热学的综合研究基础上,对未来的二期井下工程开挖中可能出现的工程地质问题进行了预测,提出了防治方案。 相似文献
59.
辽西坳陷中的断陷盆地边缘逆冲断层发育。本文描述了逆冲断层的TM影像特征,解译划分了逆冲断裂带,并指出逆冲断层对找煤远景解译推断的意义。具体分析了南票、北票矿区外围的找煤远景,还应用影像特征探索性地对逆冲断层倾角进行了解译分类。 相似文献
60.