Mining Science and Technology最新文献

A simplified method is presented for evaluation of the climatic conditions along a single underground mine airway. The method is then verified with use of a reduced scale experiments. A real-time computer routine is described, which can be used as part of a fire simulation computer program to evaluate air temperatures and humidities.

Open stoping is one of the most popular mining methods because it improves productivity and efficiency, thereby improving the economy of underground mining. Interchamber pillar recovery, as a secondary mining operation, is closely related to backfill stability, which varies mainly with the cement content in the fill. To maximize the ore recovery and production economy, a rational approach to the fill design is of primary importance.

The purpose of this paper is to provide a basis for cemented fill design. The backfill strength, in relation to fill block size exposed during pillar recovery operation, cement content and fill slurry density, is based on data obtained from experimental investigations conducted in the laboratory and several mine sites.

To accelerate the design process, a computer program is developed and the backfill parameters can be determined using nomograms as well.

To find an effective numerical simulation method for microseismicity induced by deep mining activity, results obtained by using four simulation methods, namely: (1) the energy release rate method, based on Cook's study; (2) the strain energy release rate method, developed by the authors; (3) the volume excess shear stress index method, based on Spottiswoode's study; and (4) the maximum shear seismic moment release rate method, developed here by the authors; were compared with the microseismicity in a Japanese deep longwall coal mine.

The maximum shear seismic moment release rate method was discovered to be the best method, since the intensity of microseismicity in a longwall coal panel, its variation with the face advance and the distribution of microseismic events were well simulated.

Coal gas dynamics is a fundamental theory for controlling gas in coal mines and preventing catastrophe. Starting from Darcy's law and the equation of continuity, a number of fundamental problems of coal gas dynamics are analysed using the theory of dimensional analysis and the current models for gas flow fields in coal seams are corrected. The mathematical solutions for three kinds of models of gas flow fields are studied and developed and the rationality of the new linear dynamic models is proven.

Methane concentration monitoring is one of the major centralized monitoring items in Japanese coal mines. Each colliery has many methane monitoring points at which the output signals are recorded on charts. Methane detectors usually provide valuable information on concentration, but if a gas explosion occurs unexpectedly, they could also give more information about the circumstances around the detector or scale of the explosion.

We conducted a gas explosion experiment in a test gallery to collect data on methane detector output signals. The result shows that each of the various types of detector, with their different detecting methods, have unique fluctuations of output caused by the explosion. Interferometer type and thermal conductivity type detectors indicated the atmospheric pressure change that was caused by the explosion pressure. After the indication of explosion pressure, each detector sent its corresponding response to the afterdamp. The effect of heat generated by the explosion is considered to be negligable in this experiment.

The origins of methane are examined in the context of the hazard that can result from its presence in unusual circumstances. Methane is shown to be a gas that can be encountered in a wide variety of geological environments and which should therefore be anticipated in any underground excavation.

The processes of methane generation are described in terms of the type of source organic matter and the subsequent changes that take place as a result of burial.

An important aspect of methane occurrence is the question of the origin of the gas. Various techniques for methane source evaluation are described including carbon isotope ratio, carbon 14 activity and the presence and relative abundance of higher hydrocarbons. Examples from various sources are given. Finally, the effects of migration on the parameters used in source identification techniques are examined.

Results of investigations into climatic conditions in 19 bord-and-pillar semi-mechanised panels in the Raniganj coalfield in India are presented. Variables affecting transfer of heat and moisture and resulting rises in wet bulb and dry bulb temperatures in the panel have been critically investigated and statistical methods employed to identify the five most significant variables. These are: the temperature difference between virgin rock and air; air flow rate; average rate of advance of the panel; length of air flow path in the panel; and the wetness of roadways.

Regression equations have been worked out to give: the rise in dry bulb air temperature; rise in wet bulb temperature; gain in specific enthalpy; and gain in moisture content in the panel; in terms of the five variables mentioned earlier.

Blasting experiments were conducted in a constrained condition in an opencast coal mine where the hole diameter was 250 mm and bench height was 7.0 and 14.0 m. Strata blasted contained prominent thick bedding planes and the shooting direction was always along the strike of the bedding plane. The blasting was to be carried out without muffling 50 m from the office. Detailed mapping of the attitude of discontinuities was carried out in order to confine the explosive, as far as possible, within the two bedding planes. A parameter termed “release time” has been introduced in this study to compare the degree of fragmentation of different blasts.

Vibrations due to rock blasting are studied based on the data measured on several test structures at the West Mudidih Opencast Project of BCCL, India. A single-, as well as a two-storey brick structure, a mud house and concrete walls were constructed on the edge of the working area. All the existing ground vibration predictors including the two modified predictors of Ghosh-Daemen were tested against the data recorded. A new model is proposed as a blast vibration predictor. This model is simple and an improvement on existing vibration predictors, in that it gives a better index of determination and consistent charge/delay.