Mining Science and Technology最新文献

Following on from an earlier publication on Localized Trend Analysis (LTA), this paper addresses some of the more important issues that have since arisen. Questions ranging in emphasis from details of the fundamental theory to the hardware configuration and the software necessary for using LTA are answered here. The estimation of block grades for an ore panel is illustrated starting from first principles. An interactive microcomputer application for such an estimation exercise is presented. Finally the areas of use and some characteristics of LTA are discussed. Conclusions drawn reflect two important implications, among others. Firstly, LTA as a technique does not have all the answers to questions concerning ore reserve estimation. Secondly, the fact that the method is simple to understand and implement on microcomputers, makes it quite attractive for widespread use.

Some results from studies on hole deviations are discussed. A system which automatically controls drilling parameters during percussion drilling was developed. A procedure for determining the operating magnitudes of drilling parameters for presetting on a drilling machine is demonstrated. Field experiments show that the automatic control system gives less deviations than ordinary drilling systems.

As a result of changes in the pattern of flow of underground water associated with Littleton Colliery, a series of investigations were carried out to study the pattern of water flow in the north-west of the Cannock Chase Coalfield, of which Littleton is a part.

The likely consequences of any change or termination of pumping operations had to be determined. Indications were that “live” connections for water courses existed and that pumping operations could be consolidated. It was decided that a tracing survey would be carried out to determine both the magnitude and effects of the increased flow rate. A hitherto untried method of tracing the passage of water through mine workings was chosen.

This paper sets out to explain the techniques and results of the survey.

A numerical method of solving the time-dependent gas flow equation with respect to a medium having variable, anisotropic permeability is described. The approximate solutions for this equation are obtained using finite element analysis to give time-dependent gas pressures. A finite element package called pafec'75 was used to facilitate gas pressure distributions, simulation of boreholes and calculation of gas flow for a given boundary. The similarity between the gas flow and the heat flow equation enables gas flow problems to be solved using thermal routines from the pafec'75 program suite, after suitable modifications.

An explicit expression relating drilling parameters at the bit-rock contact is derived. The expression estimates the minimum torque, related to bit-rock contact only, required to maintain constant bit rotation. Theoretical results from the developed bit-rock contact relation agree very satisfactorily with those obtained from field tests and other previous experience.

The outbursts experienced at #26 Colliery originated from within sandstone river channels just above the coal seam. The outburst mechanism proposed here can be used to model the outbursts experienced at this mine quantitatively. The mechanism treats an outburst as a series of instantaneous, static events driven by tensile failures within the rock mass around a spalling cavity. Outbursts may terminate simply due to stress re-distribution caused by the changing shape of the spalling cavity; if a stable shape is achieved. Alternatively, spalling could continue indefinitely unless it is terminated by a change in geology. The two main factors affecting the occurrence of an outburst are the gas pressure and the tensile strength of the rock containing the gas. The final stable shape of the cavity, when not geologically influenced, is directly dependent on the in situ stress field. Sensitivity analyses illustrate the above influences.

This paper proposes a theoretical model which relates the sub-surface subsidence at any horizon to the subsidence at the surface caused by underground mining. Mathematical equations are derived based on certain assumptions that would enable the prediction of sub-surface subsidence from surface subsidence. The inclination of the extracted seam is taken into account in the analysis. The relationships derived between sub-surface and surface subsidence are applied to actual data from both sub-surface and surface subsidence available from three collieries, using the measurements from boreholes drilled from the surface. The comparative study indicates good agreement between the theoretical model and in situ measurements.

Self Potential (SP) and horizontal apparent resistivity measurements were made along a NW-SE oriented line perpendicular to the surface trace of the discontinuity in the Gelik District of the Zonguldak Coal Field. The dip angles and locations of the lateral discontinuities in the survey area were found by interpreting the SP and resistivity anomalies. Also, the boundary between Cretaceous and Carboniferous strata was determined and a cross-section along the NW-SE line was constructed.

Uncertainty is inherent in mining investment decisions because the knowledge obtainable on conditions which affect choice is limited. The most common techniques for incorporating uncertainty into the investment decision process are here described. The basic features of decision-making under incomplete knowledge are then examined and a new approach to making mining investment decisions is proposed. The proposed approach is based on an a priori ranking of the likelihood of future circumstances and is very straightforward in application. An example is presented and the interpretation of the model is given.

Exploitation of a huge opencast browncoal mine in central Poland is facilitated by a detailed analysis of the Tertiary and Quaternary overburden. The overburden could not be removed effectively using the common methods for forecasting the material and structures to be encountered. The geological structure in the area is so complex that additional measures had to be taken to ensure safe and effective exploitation. Studies of the Quaternary geology — detailed, but still following the normal style — carried out during the preparatory phase and continuing during working of the mine, were shown to provide sufficiently accurate prediction of future mining conditions by defining a 3-D build up of the overburden.

Knowledge of the Quaternary could be used to obtain accurate information on the structural development of the Tertiary and the Mesozoic. However, it was also necessary to have a clear insight into the characteristics of the hard-rock substratum as this made some structures in the Quaternary more understandable.

The analytical studies carried out within this framework had to be fully integrated, because of the interdependence between the conditions of browncoal exploitation and the (primarily structural) characteristics of the browncoal and the overburden. Slope stability, geotechnical safety and comparable properties could thus be greatly improved.