Mining Science and Technology最新文献

Methane gas is emitted when coal is broken at the face of a coal mine. To prevent a situation where a methane gas explosion can occur, the face and heading must be ventilated effectively. In this paper an investigation is conducted to determine if the ventilation in the heading of a coal mine can be increased by the utilisation of air scoops. Two scoops are investigated, one upstream of the heading and one downstream of the heading. The influence of the air scoops on the flow field in the heading is determined numerically. The results show that based on penetration depth and absolute average air velocity, ventilation can be improved by the utilisation of air scoops and that it is better to locate these scoops downstream of the heading.

Costs of using coal from the eastern United States, Australia, Colombia and South Africa by electric utilities in the coastal areas of eastern United States and Europe are determined on a comparative cost basis and analyzed. Costs considered include coal production and transportation costs and cost to the electric utilities, determined by differences in coal quality (i.e., heat, ash and sulfur content). Estimated costs and shadow prices are determined and compared with actual prices.

Differences in determined costs indicate that United States high sulfur coal will be uncompetitive in all scenarios investigated, United States low sulfur coal will be competitive under certain circumstances, and that potential economic rents may accrue to coal producers in Colombia, Australia and South Africa.

A 3-D boundary element method of viscoelasticity is presented for analyzing the time-dependent deformation and stress state around underground mine workings. It assumes that the rocks are stratified with bedding planes and reinforced by fully or partially grouted rock bolts. The Kelvin-Voight and Burgers models are used to represent the viscoelastic behavior of rock strata. Boundary integral equations for these types of separately homogeneous media are developed based on the correspondence principle of viscoelasticity. The time-dependent functions involved in the equations are obtained through the use of the Laplace transformation technique. Thus, the method can compute the stress state of a rock structure without the need to discretize variables which alter with time. An example is presented to show the application of this method to mining engineering.

Coal has been mined continuously in Wyoming since 1865. Nearly all the coal produced in the first 90 years of mining was from underground bituminous mines. Subsidence has been a threat in Wyoming since the beginning of coal mining; constituting an extreme danger to public health, safety and property. As a consequence, Wyoming mine subsidence problems qualify for the highest priority of funding under the Surface Mine Control of Reclamation Act of 1977.

Abatement projects have been undertaken by the Wyoming Abandoned Mine Lands (AML) Program to prevent or minimize further subsidence in Wyoming communities. This paper gives a brief historical account of mining activity in Wyoming. Subsidence characteristics and occurrences in various communities are presented. The locations of key abatement projects and the reasons for their selection are then given. The selection criterion for the backfilling and grouting methods and the techniques themselves are presented, and the problems encountered during various projects are discussed. Successful projects are analyzed and recommendations for future projects are given.

The application of a prototype knowledge-based expert system for spontaneous heating, essh, in surface coal stockpiling operations is described. A brief review of earlier studies concerning the assessment of self-heating risk in stockpiles is presented. Based upon extensive analyses of the incidents of coal storage problems with spontaneous heating, the paper identifies the significant contributory factors which may have caused them. The stacking and precautionary techniques, or the rules of thumb, accumulated from years of experience and research, with particular reference to the safe storage of coal, are also discussed.

This high level knowledge is further refined and consolidated into a knowledge-based expert system which aims to replicate the reasoning of human experts in reaching a decision. The system assesses the spontaneous combustion risk by using certainty factor techniques. It is capable of identifying common faults and recommending systematic procedures and methods for inexperienced engineers in handling stockpiles being planned, under construction and in use. Future development of the current system in surface mining operations is highlighted.

The approach outlined in this paper offers a new managerial technique and shows how the incidents of spontaneous heating, weathering of coal and environmental impact can be minimized or avoided entirely through appropriate storage and handling, by applying an expert system approach.

The performance of Roadheading machines in face gate roads, cross-measures drifts and major access roadways is of importance to the profitability and productivity of modern mechanised longwall mines. Slow advance rates due to arduous cutting conditions results in cost increases and delays. An understanding of the mechanisms contributing to cutter pick deterioration is vital.

Over the past decade much emphasis has been placed on wear problems associated with the excavation of rock and this had led to a concentration of the study of abrasive wear of cutting tools. However much of this initial work was applied to surface mining problems and it is felt that it is not directly applicable to the conditions encountered when cutting rock with boom-type roadheaders where the cutting and transient forces are higher. Indications suggest that a composite mechanism for tool wear occurs, with abrasion, impact loading and frictional heating all playing an interlinked part in the wear and ultimate destruction of cutting tools.

In the Tverrfjellet Mine, mid Norway, serious stability problems have developed in connection with large open mining stopes. The problems may be related to high in situ horizontal rock stresses combined with unfavourable geometry. To stabilize the most critical area cable bolting has been used. Closely associated with the stabilizing measures is a caving warning system based upon eight borehole extensometers. Deformations in the rock mass in excess of 1 mm on any one of the extensometers will trigger red stop lights in vital haulageways passing through the threatened area. In the most critical area the deformation is continually monitored. About 1 ½ yr of operation have shown a steady decrease in deformation rate, indicating that the cable bolting works as planned. However, small deformations still take place, necessitating keeping the warning system operative until new by-pass haulageways are established.

The rock mechanics program in the mine also includes rock stress measurements and monitoring of stress change. A modified version of the doorstopper used for stress change monitoring has proved very promising.

A coal seam is usually sandwiched between two relatively stronger beds: the roof and floor. Drivage of a rectangular roadway into coal creates a different mining stress situation than that appearing in homogeneous and isotropic rocks with circular, elliptical or rectangular openings. In the present paper, the vertical stress distribution in coal forming the side of a rectangular roadway has been derived, taking into account some assumptions and applying the principle of a “beam on an elastic foundation”. The change of the state of confinement of coal from biaxial at the edge of the roadway to triaxial inbye has been accounted for in the method and the result is the reduction of the maximum vertical stress at the roadway side compared to a continuous biaxial or triaxial confinement. The stress distribution curves using different parameters are presented and the influence of some of parameters on the maximum vertical stress has been analysed.

Fill placement using a very concentrated slurry for underground mines has been recognized as a favorable approach to improve backfill quality and economy. For this reason much effort has been devoted to preparation of high density slurry. This paper introduces the fluidization technique as a more effective and economic technology for producing tailing slurry of a high density and describes the fluidization mechanism, experimental system and results obtained during backfill. Test runs were carried out both in the laboratory and at a mine site with tailings of different size, which were allowed to settle down in a silo. A water jet was used to disperse solid particles and keep them in suspension and flowable under the action of gravity. The main factors affecting slurry density are fluid velocity, pressure and discharge. The technique introduced here has been used in backfill preparation and the density of slurry formed by fluidization has reached 75–80% solids by weight.