排序方式： 共有12条查询结果，搜索用时 19 毫秒
1.
A. Vervoort 《Geotechnical and Geological Engineering》1988,6(4):313-326
Summary The forming of roof cavities in longwall faces is a complicated process. A likely explanation for this process is the presence of relaxed zones in the first beds of the roof above and ahead of the support. If existing or potential fissures are allowed to open through insufficient constraint, the block of roof delimited by these fissures will collapse. An increasing unsupported distance, an increasing distance between the face and the first row of legs, a lower vertical bearing force and a lower support pressure on the roof will increase the extent of the relaxed zones. These effects are investigated through underground observations and numerical modelling.Supplementary to this local influence, there is also a spatial relation between the support characteristics of one element in one coal step and the occurrence of fall outs in the roof uncovered by the next coal steps (3 on average) and above the neighbourhood elements (2 to 4 on average). It is probable that, once a cavity is formed, it is extended easily (in the two directions), until appropriate measures are taken. 相似文献
2.
Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (“TeV plerions”). The study
of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in
these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our
analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions
and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6
powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN “Rabbit” G313.3+0.1 which is possibly powered by a young pulsar. 相似文献
3.
4.
5.
分析了大口径嵌岩钻进面临的主要技术难点,并对目前国内常用的３种大口径嵌岩钻进方法－牙轮／滚刀钻进法、冲击钻进法（包括无循环和反循环）和气动／液动潜孔锤钻进法的技术现状作了介绍,提出了提高我国大口径嵌岩钻进技术水平的建议。 相似文献
6.
D. N. Bigby 《Geotechnical and Geological Engineering》1987,5(1):59-73
Summary Recent developments in powered supports on British longwall faces include the advent of lemniscate designs, increased setting and yield loads, larger maximum extraction heights and a consequent rise in weight and cost. There was a requirement to examine the relevance of existing strata control theory to modern conditions. Measurements on five longwall coalfaces at four British collieries are described. Accurate measurements of support pressures, closures and inclinations, roof/floor convergence and lateral movement and hydraulic supply parameters were made with a digital data logging system. At one site magnetic extensometers were utilized to measure face and roof strains. Consideration of measured roof dilation and reclosure in conjunction with convergence provides a new perspective on the deformation mechanisms involved. The most important parameters governing strata conditions were identified as proximate lithology, foundation characteristics and adequate setting load densities. Recommendations are made regarding choice, design and operation of powered supports. 相似文献
7.
S. S. Peng 《Geotechnical and Geological Engineering》1987,5(1):29-57
Summary Field investigations on seven U.S. longwall coal faces were carried out to examine the behaviour and interaction of roof, floor and support on longwall faces equipped with hydraulic powered supports. The most important factor in determining face stability was found to be periodic weighting and an empirical design equation was developed for support capacity. The interaction of various elements in the face system is examined and discussed. 相似文献
8.
Summary The selection of powered supports involves many geological factors where adequate data is lacking and in which subjective judgement is inevitable. This paper proposes one approach, a fuzzy multicriteria decision-making model, to transfer non-quantitative judgements into quantitative ones that computers can process. A detailed example is included to demonstrate how the model applied to evaluating the suitability of powered supports to coal seams. 相似文献
9.
10.