Mining Science and Technology最新文献

The outbursts experienced at #26 Colliery, Glace Bay, Nova Scotia originated from within sandstone river channels just above, and sometimes penetrating, the coal seam. These outbursts caused delays in driving the main headings, a considerable loss of revenue and threatened the closure of some areas of the mine. A major mine fire has since closed this mine; however, other mines in the Sydney coal field are expected to experience similar problems.

Part 1 of this paper summarises the geology of the Sydney Coal Basin and the geology associated with the outbursts. A brief description of the 37 recorded outbursts is presented. Little data is available to classify the conditions at the outbursts sites but that available, on the rock properties, gas pressures and field stress conditions, is summarised here.

A better understanding of the mechanisms of these outbursts could pave the way to creating a safer and more profitable operation at neighbouring mines. Part 2 of this paper proposes a mechanism that explains these occurrences and a model is developed to analyse the influencing parameters. Part 3 compares the results of the model studies with field observations.

Coal pelletization offers a solution to the handling problems associated with coal fines. The literature suggests that feedstock moisture content limits are dependent upon the ash content of the material. It was felt that this dependency should be tested for British froth floated coals. Different coal samples were collected from various British Coal mines. Analysis indicated that a wide range of froth floated coal types had been selected. Pellet growth rates, fracture loads (green and dry) were examined. Results showed that pellet strength was directly related to both pelletising time and feedstock moisture content as well as being influenced by particle size, finer particles producing stronger pellets. The size/strength relationship followed the form Y = KDⁿ where n varied between 1.09 and 2.30. Unsuccessful attempts were made to relate basic results to the ash of the feed material.

The outburst mechanism and model proposed in Part 2 of this paper has been used to simulate the outbursts at #26 Colliery. The cavities generated by the model were compatible with the actual outburst cavities in both size and shape. The model was also used to explain the presence of different size cross-sections within the same cavity; they are a result of the changing width of the sandstone exposed above the heading. The narrower the exposed sandstone, the smaller is the resulting cavity. In addition, the model shows that if an outburst is not terminated by a change in the excavation shape, it could spall indefinitely unless terminated by variations in the geology.

A siltstone bed often occurs between the sandstone channel and the coal seam. If the sandstone is not penetrated, then the overlying siltstone must fail prior to initiation of spalling (outbursting) from the sandstone. This siltstone failure has been analysed as a ‘cutter roof’ failure of a beam loaded by the gas pressure at the sandstone/siltstone interface. Results from this analysis are also compatible with the field observations.

Remedial measures should be taken when mining near an area prone to outbursts. Several potential remedial measures are discussed in the light of the model results. Further evaluation of these potential remedial measures is needed by means of on-site testing. However, the prime concern regarding the previous practice is that the entry support immediately behind the face was passive; it is thought that the installation of an active support as close to the face as possible would be a benefit.

One aspect of cutter pick application, namely, cutting of high-strength rocks at low and negative rake angles is examined, and the validity of Evans' cutting theory which is based on the assumption of tensile failure is discussed.

It is shown theoretically that at low and negative rake angles, rock failure is most likely to take place as a result of compressive stresses created by the geometry of the cutting pick, rather than tensile stresses.

The findings of some available laboratory experiments are also shown to be in agreement with the theoretical suggestions made in this work.

A classification system based on the relevant rock mass and material properties of the ground and their influence on excavation equipment performance is described. An excavation rating system is proposed utilizing some rock mass and material properties which influence excavation performances; namely, uniaxial compressive strength, hardness, discontinuity spacing, degree of weathering and seismic wave velocity. The work was carried out in operating Turkish surface lignite mines. It is suggested that this system, which is supported by 284 different case studies, can be used for rapid determination of the excavation class, together with the type of equipment to be used.

Given in the paper are the results of experimental blasts in a limestone quarry for control of production of fines. The study indicated that fines can be kept to a minimum by reducing the charge factor to an optimum value, and by adopting a particular blasthole geometry. However, geological features imposed a limit on the reduction of fines.

A new technique for measuring the flowrate in underground airways has been developed. It takes advantage of a very sensitive differential pressure measuring transducer, equipped with a microcomputer. After a brief description of the sensor and its control unit, some of the technical characteristics investigated by tests carried out in the laboratory and in the field are discussed. Special attention is paid to the appropriate set-up of the equipment.

By means of XPS electron spectroscopy, together with observation and measurement using an electron microscope, the cause of a decrease in the output activity of catalytic methane sensors was investigated. The principal cause of this decrease in activity was identified as carbon deposition on the catalyst surface during operation.

On the basis of these observations and theoretical calculations a high stability sensor with flowing potassium was proposed and developed. Additionally, the optimum composition and method of preparation of the sensor was determined. As a result, the sensor's stability and working life were greatly improved.