Mining Science and Technology最新文献

Clay present in sandstones is sensitive to the water saturation and to the kind of ions and their concentration in the flowing water. The reaction of the rock upon these factors manifests itself as an internal swelling or internal shrinkage of the rock and the resulting permeability changes in the water flow.

This paper describes experimental investigations into permeability changes occuring in the flow of water and water solutions of salt of various concentrations in sandstones collected from oil reservoirs and from hard coal mines. Experiments with the flow of water and of solutions in coal are also mentioned.

Increasing the water content in sandstones from an air-dry condition to the state of full saturation results in rapid (within hours or days) internal swelling of the rock leading to a decrease in permeability which can achieve two or three orders of magnitude. In the flows of water solutions of salt in sandstones it is possible to produce changes in permeability (increase or decrease) even by two orders of magnitude by means of changing the concentration or the ion composition of the solution.

The flow of a diluted solution of calcium hydroxide proved to be very effective in increasing permeability. Big effects were obtained even when using low concentrations of this solution, which suggests the possibility of a practical application for the observed phenomena.

Investigation in the “coal seam gas” physical-chemical system existing in gas-containing coal seams is one of the most important problems in mining science. The fact that the combination of methane with the coal seam and the influence of the seam development conditions upon gas transfer in the coal seam have not been sufficiently investigated, hinders the development of coal deposits and a wide utilization of methane from those deposits for energy. In particular, the problems of methane sorption process thermodynamics in the microporous structure of coal; gas-containing coal seam deformation mechanics; the nature of coal and gas outbursts; and the intensity of methane extract from coal deposits remain unsolved.

Any advance in the development of methane resources is impossible without understanding of the problems of the methane state in gas containing coal seams.

In opencast mines the mining activity often proceeds below the original piezometric surface of the aquifer in the area. Massive dewatering operations from the aquifer are resorted to in order to lower the piezometric surface and thus to prevent flooding of the working places. The influence of pumping ususally extends beyond the mining limit. To determine the extent of influence, it is suggested here to apply the geostatistical method: the semi-variograms of the drawdown levels. A case study using this method is presented and the variation of the area of influence with pumping is shown. An empirical relationship between the area of influence and the cumulative quantity of water pumped has been obtained for the mine.

This paper overviews the condition monitoring techniques and presents some examples of current longwall mining machinery applications. An expert system for condition monitoring purposes is discussed together with several case histories for underground mining machinery maintenance programs. The development of the instrumentation for longwall condition monitoring is reviewed and strategies of the development of the condition monitoring and expert system for longwall mining machinery are proposed.

The effects of equally arranged circumferential pick spacing on boom tunnelling machine cutting heads are described, through a series of laboratory and in-situ trials. The equal circumferential spacing is emphasized to be an important parameter significantly influencing cutting head balance and is limited by the total number of arcing picks and tool-lacing. A number of alternative lacing patterns is outlined and then compared in terms of cutting efficiency and manufacturing feasibility. The long-term practical investigations indicated that within the size of the commercially available tool-holders, up to 26 or 27 heavy-duty picks may be laced at equal circumferential spacing on medium-duty roadheader cutting heads. The problem of tool-holder overlapping was further found to reduce with a threestart arrangement employing a higher angle of wrap. The underground trials also indicated that threestart cutting heads laced with a total of 24 arcing picks may not be so efficient at higher arcing speeds as the other heads investigated.

During a study of the properties of solder, used as a binding material between a solid pseudo alloy plate and the steel base head of a monoblock bit, the focus was put on determining the qualitative-quantitative solder composition, measuring solder thickness in the clearance between the solid pseudo alloy plate and steel base, and measuring the hardness of the solder itself. Those parameters have a predominant effect on the quality of bonds, as well as on the exploitation life of the monoblock bit during percussion drilling in mining.

Measurement of the above parameters was performed on heads of monoblock bits that had been used for drilling in the working conditions of the various physicomechanical and abbrasive environments of Yugoslav mines.

A methodology has been used to compare the quality of mining equipment based on technical characteristics. The method can correspond to the many demands of comparisons between different types of mining equipment based on their quality.

An adiabatic calorimeter has been designed to enable the spontaneous combustion propensity of coal to be established. The experiment was designed to run unattended, with a personal computer being used for measurement and control functions. All measurements are stored on a data diskette while the experiment is in progress.

The calorimeter was designed to be run in both a rising temperature mode and and an incubation mode. Various indicators of self-heating potential, such as total temperature rise, initial rate of heating, minimum self-heating temperature, and kinetic constants can be investigated.

Results obtained from the adiabatic tests will be compared with the results of crossing-point temperature determinations and differential thermal analysis (DTA) tests for the same coals, with a view to formulating a mathematically consistent spontaneous combustion liability index. This paper describes the major components of the adiabatic calorimeter.

A new method is proposed for more effective breakage of rock boulders during secondary blasting. It is suggested that by placing two contact charges at symmetrical locations on a boulder's surface, one can take advantage of stress wave interaction within the block and, especially, the superposition of reflected tensile waves from the free boundary of the boulder. Theoretical calculations based on elastodynamics and dynamic photoelastic experiments showed the existence of stress concentration within a finite block under symmetric loading conditions, which could lead to spliting of the block along loading points. Blasting tests on mortar models of various shapes further confirmed the possibility of rock boulder fracture by this method.

The aim of this work was to investigate the size distribution of dust particles produced during the drilling process. It has already been proved that the degree of harmful effect of inhaled dust is closely related with dust particle size. The dust data needed to determine size distribution were obtained by sampling dusty atmospheres during the drilling process with a short-period thermal precipitator.

Drilling and dust sampling processes were carried out in a model gallery which simulated the working face. Rock samples used in drilling were brought from the various galleries of Kozlu mines, Zonguldak Colliery. The tests were carried on four types of sandstones, two types of shales and conglomerate, in total seven types of sedimentary rock. For each type of rock six dust samples were taken and evaluated.

It is concluded that the frequency distribution of airborne dust particles produced by each rock type is approximately lognormal. The geometric mean values of dust particles for sandstone, shales and conglomerate are found to be 0.89, 0.95 and 0.83 μm respectively. In other words, the mean value of dust particles produced during the drilling operation of different rocks are around 1 μm in diameter, which has the maximum probability to be retained in the lungs during respiration.