Mining Science and Technology最新文献

A review of the application of existing subsidence prediction methods available is presented. A brief description of all the three methods—empirical, functional and mechanistic—is given and merits and demerits of each method are discussed. A review of the applications of each method in different parts of the world and recommendations for research on further improvements in each method are given for the state of the art of subsidence prediction. Methods using the functional approach, especially those of influence function, are found, at present, to be the most reliable and practicable, however there is still scope for improvements in this approach, to incorporate the effects of various subsidence-inducing parameters by the use of complementary functions.

Sliding along a stepped path formed by two or more joint sets is more common than an ongoing discontinuity in rock slopes. The solution to the problem of sliding along a stepped path formed by two joint sets (i.e. one major and one cross joint set) has been studied previously. However, exists no work exists on the analysis of stepped path sliding with three joint sets.

To solve the problem of stepped path sliding incorporating three joint sets two approaches are described in this paper. In the first approach a simulation model which generates possible stepped paths is proposed. In the second approach the problem is first separated into two sub-problems (namely, major joint with one of the cross joints as subproblem no. 1, and major joint with the other cross joint as sub-problem no. 2) for which the probability of failure can be easily obtainable, and then the probability of failure for three-joint case is calculated using the results of two sub-problems. Formulations for the second approach, which is much simpler than the first one, is given and used to solve some example problems. Results indicate that the inclusion of a second cross joint set increases the probability of failure.

Ranigunj coalfield (India) has been facing significant problems due to subsidence as a result of underground mining of coal seams. The occurrence of the thick seams in close proximity, shallow depth, great variation in the nature of superincumbent strata from site to site, followed by the slow rate of extraction, has aggravated subsidence problems. In the recent past, many such workings have collapsed damaging a large number of surface structures.

In view of the aforesaid need, a comprehensive project financed by the Ministry of Energy (Coal), was undertaken by the Department of Mining Engineering, Indian Institute of Technology, Kharagpur, at a Colliery in Ranigunj Coalfield.

This investigation revealed that the caving horizon occurred at 4 times the extracted seam height, which differs from the findings in the U.K., U.S.A. and Australia. Also, it appears possible to estimate strata displacements from geological and physicomechanical information from the overlying rocks using the bending moment principle. Further, it was observed that the shallow workings could give rise to a “sink hole” type of subsidence, which is dangerous and could adversely affect the environment, safety of the public and properties.

The results of a study undertaken to assess material diggability for bucket wheel excavator (BWE) performance by the direct cutting method are presented. The specific cutting energy (MJ/m³) obtained by the standard cutting test was compared with the results of the O&K wedge test and a good correlation was established. The cutting specific energy was then used to develop the material diggability classification. This classification can be used to assess the diggability of an overburden strata by a BWE.

The efficiency of auxiliary ventilation by a brattice is given in a simple exponential expression. This expression is derived from and compared with the complete analytical solution of the leaky brattice. The equation requires only measurable properties of the drift and the working face flow requirements.

There is excellent agreement between the approximate and exact solution. The maximum relative error is less than 0.3%. There was also good agreement between the approximate solution and experimental data from three drifts in potash mines. The average difference in the pressure differences and the flow is about 7%. It is shown that the fitting equation is more accurate than the experimental data.

Faced with rising costs and lower metal prices, several Ontario base metal sulphide mines have changed their method of mining to vertical crater retreat mining. This is a bulk mining method that utilizes large diameter holes and mines successive cuts remotely by blasting and cratering the bottom of the drill holes. The ore body is mined from the bottom up. The method in turn has required a change in materials handling to cope with the greatly increased productivity.

This paper presents an overview of vertical crater retreat mining in the Sudbury area using examples from several producing mines. The paper reviews the history of vertical crater retreat mining, various methods of applying vertical crater retreat layouts, the development of in-the-hole drills capable of drilling the large diameter holes required, methods of explosives loading and blasting to achieve the required cratering effect, methods of ground support including backfill placement, and the ore loading equipment presently being utilized including remote control load-haul-dump units and continuous loaders.

The safety aspect of vertical crater retreat mining has been of concern, and was the focus of a provincial inquiry. The benefits in improved safety are demonstrated through an analysis of various records kept by the mines and provincial agencies.

Future trends can now be envisaged, particularly in relation to deep mining. Some experimental work, which could have practical applications, is described.

Toxic fumes from blasting operations in underground mines are among the most common and serious hazards encountered underground. In general, blasting operations in most mines result in up to several thousand tons of broken rock and large volumes of toxic fumes. The implications of the high concentration of toxic gases emitted from blasting on the mine ventilation system are very significant an in many cases have had catastrophic results. When analyzing and designing the primary and auxiliary ventilation system for an underground operation, the dilution requirements for explosive agent gases have to be taken into consideration. In an operating mine dilution ventilation is one of the most effective control measures against blasting fumes and blasting fume dilution times after blasting must be calculated. This requires accurate determination of the concentration of toxic gases produced by the explosives used. This paper describes the development of an effective model for predicting toxic fumes from commercial explosives and for determining the ventilation requirements to reduce the gas concentrations to the limits required by law. Extensive experimental testing, computer coding and field verification were the tools used for the successful development of the proposed model.

This model represents a powerful tool for use in identifying and predicting problems associated with toxic gases underground so that corrective measures can be taken, and constitutes an important tool for the mine engineer to ensure that safe and satisfactory environmental conditions are maintained underground.

One of the most important aspects in the selection of suitable machines for coal and rock cutting is the determination of the cutting characteristics of the material. This paper describes the research carried out into the design of a system for testing rocks under conditions which resemble, as closely as possible, those under which mining machines operate. The equipment was required to be portable and capable of being used under a wide variety of conditions; being hydraulically powered, the system could be used on the coal face or in conjunction with tunnelling machines. Initial surface trials highlighted a number of problems which were subsequently eliminated by improved design of the system. Subsequent underground trials proved that the equipment was reliable and capable of measuring quantitatively the magnitude and variation in cutting forces in different materials.

This study aimed to establish methane adsorption isotherms for coal samples taken from four different seams in Kozlu district, Zonguldak Coalfield, Turkey. The quantity of methane adsorbed by these samples, at different gas pressures up to 45 atm, was determined and the results were discussed in relation to the gas capacities of these coals. The methane adsorption capacities of Zonguldak coals were compared with the gas capacities of some British and American coals. Methane adsorption isotherms were measured at constant temperature of 25°C.

The effects of the moisture content of a coal sample on the methane adsorption capacity of coal was determined for Çay coal and it was seen that a moisture content of 1.79% reduces by about 13% the quantity of methane adsorbed by coal. It was also found that for particles smaller than 65 mesh size, the quantity of methane adsorbed by coal does not change. By using the empirical equation suggested by Ettinger, adsorption isotherms for temperatures other than 25° were also drawn.

Based on the mechanical properties and the load-carrying conditions of the rock masses of a copper mine in China, this paper studies the influence of boundary weakening on the caving process with a three-dimensional elastic finite element technique (TDEFE), presents the breaking and caving mechanisms of the ore body, together with their criteria, and discusses the rationale for optimizing the arrangement of the boundary-weakening slots.

This paper also provides the theoretical bases for the design, production and ground control of the block caving at the similar mines.