Mining Science and Technology最新文献

Blast design components: primer location, collar stemming, charge weight and hole diameter, were varied during three independent investigations to study their effects on the generation of ground motion, air blast and fly rock over small scaled distances.

The location of the primer in the explosive column, charge weight and charge diameter, were found to have the greatest effect. Furthermore these studies also indicated that:

• (1)

  borehole pressure is the major source of induced ground motion;

• (2)

  as long as the air blast is controlled, it is quite likely that ground vibrations will remain at minimum levels;

• (3)

  air blast and fly rock effects resulting from the collar priming are expected to be greater than those resulting from bottom priming of the explosives.

Neyveli lignite field in southern India, is the major source of supply of lignite in India. Mining of lignite from the Neyveli lignite field involves pumping of groundwater from the water-bearing formations. The area of influence created by pumping depends upon the volume of groundwater pumped. The paper discusses the development of a empirical relationship between the total volume of groundwater pumped and area of influence. This paper also explores the possibility of applying this relationship to predict the area of influence for future mine planning and dewatering operations.

In mine ventilation, the head loss due to friction is usually calculated using Atkinson's equation. But only in an ideal case is this equation valid. In the present analysis a power law constitutive relation based on Atkinson's equation is introduced and a differential equation for the head loss gradient is derived. The constitutive law proposed here provides a more general description of air flow characteristics in mine ventilation.

The causes and mechanisms of pillar failure in a section at the Emaswati Coal Mine in Swaziland are discussed. The study indicates that there exists an intricate relationship between the local geology and ground instability that needs to be addressed if future pillar failure is to be avoided. The conclusions are mainly based on extensive in-mine investigations and finite element computer modeling using the mechanical properties of mine roof, coal, and floor. The study has indicated that pre-mining failure, coupled with the possible loss of strength due to the heating of the coal seam (which was caused by the hydrostatic emplacement of dolerite dykes and sills) adversely affected the bearing capacity of subsequent coal pillars.

An analytic approach to assessing and predicting the operational effectiveness of continuous mining systems is presented. Availability models and productivity models have been developed through use of the techniques of direct reliability assessment and Markov modeling. The application of these models is illustrated by a field study.

A case study of an opencast mine is presented where work is being carried out using an interconnected system, with mined ore fed directly to a processing plant. Breakdowns in the mining process or in the plant affect the overall mine production. To separate the two interconnected units, an intermediate stockpile before the primary crusher of the plant has been proposed. The stockpile should be of an adequate capacity to provide the necessary coverage for the breakdowns, but should not be too large or rehandling costs will be too high and it will take up too much space. The minimum size of the stockpile required has been estimated using detailed statistical analysis.

In the U.K. the preparation and preservation of mine plans is strictly controlled by legislation, and every new plan must be orientated to and correlated with the Ordnance Survey National Grid. In order to implement this requirement, the mine surveyor requires a knowledge of the projection system used by the Ordnance Survey and of the computations involved in determining local scale factors, convergence and other variables. The aim of this paper is to explain clearly, approximate and precise methods of correlation, by means of worked examples.

Based on the extended formula of the Power law, partial differential equations for a compressible gas flow in homogeneous and heterogeneous coal seams have been set up. The measured parameters of coal gas dynamics were used to check the accuracy of the new nonlinear dynamic models for gas flow fields in coal seams. The results of the comparison revealed that the new nonlinear theory for coal gas dynamics is closer to the actual situation than the other two existing theories.

The mathematical description of dynamic fracture processes, in particular of rock bursts in hardcoal mining, can be advanced by the use of dynamic iterative methods. From a comparison of two different numerical approaches the dynamic finite difference method as used in the FLAC program turned out to be the most suitable. For proper calculation of rock bursts one has to consider, besides a shear break criterion, the simulation of the triaxial, post-failure mechanisms of coal and rock strata as well as the behaviour of contact planes between coal and rock strata.

The results of laboratory drilling tests on triaxial loaded coal samples have been used for this. To understand the genesis of rock bursts lateral inhomogenities either in the seam or at the interface must be taken into consideration as well. If all of these parameters are not included in the model no dynamic fracture processes similar to rock bursts will occur. This also explains the unpredictable nature of rock bursts a rock burst will not necessarily occur when specific relationships between area being worked, geometry, stress and strength exist.