Mining Science and Technology最新文献

The new simple mathematical expression for geoethermal distribution in country rock in deep tunnels can reflect the essential relation of the rock temperature to the geothermal parameters, radial distance and ventilation time. The results obtained both by numerical simulations and through in -situ measurements prove that the new mathematical expression for geothermal distribution is close to reality.

The current barrier pillar design criteria in longwall mining are described with the aim at developing new design criteria for barrier pillars. Two analytical approaches have been developed and are presented. The results are compared with the in situ data obtained from monitoring the performance of 26 gateroads (coalface access tunnels) in mines of the Cape Breton Coalfield. Finally, the results of these approaches are compared with existing barrier pillar design criteria in longwall mining.

Some dynamic and kinematic characteristics of longitudinal and transverse cutting heads on boom tunnelling machines are described and compared. A dynamic and kinematic analysis was carried out for the both cutting head types under the same operational and design conditions. The results were compared with those of long term in situ trials of longitudinal cutting heads.

The cutting head design was found to have a significant effect on the performance of both cutting head types. The resultant boom force reaction was found to act perpendicular to the boom axis for a longitudinal head, whilst it tended to act parallel to the boom axis for a transverse head. The change in the magnitude of the resultant boom reaction was also seen to be relatively high for the transverse heads during transitions from arcing to lifting. It was further emphasized that the consistency in the produce size of a transverse head is likely to be higher in arcing than in lifting.

There is an opinion that the Brazilian test is not valid for materials where the ratio, n = R_c/R_t, between compressive strength, R_c, and tensile strength, R_t, is low. This article supports the view that the Brazilian test is valid for materials which exhibit brittle failure. The continual δ model and β model created on the basis of the effective tensile stress are proposed. According to the latter model: R_t = (2P/πDL)(n + 3/n), of which experimental proofs are given.

Sill mats are structural elements used in cut-and-fill mining of low to moderate width, steeply dipping ore zones in order that ore sill pillars may be mined out. Traditional sill mat design appears to have developed from experience and timber mats are often used to ensure stability. Centrifuge model studies are combined with equilibrium analyses in this paper to provide insight into sill mat behaviour. Physical model testing provides particular insight into potential modes of failure under complex boundary stress or displacement conditions. The results show that sill mat reinforcing might be considered as an alternate to timber mats in cases where plain cemented sill mats would not be expected to be suitable.

During pillar extraction, an increase in strata movement occurs. To accomodate this increase, supplementary support is often required in intersections of pillar extraction panels. This paper summarizes an investigation to determine an optimum support system. It shows that the installation of cable bolts and cable trusses as supplementary support improves the roof stability by reducing the roof deflection. The roof deflection was measured underground and the results obtained formed the basis for three-dimensional numerical simulations.

The idea of transmission of the diametrical load on a specimen, by both stiff and soft loading devices, is based on theoretical and experimental investigations. A failure in the contact area of the specimen is excluded if its modulus of elasticity differs considerably from the modulus of elasticity of the loading device, regardless of the trend.

A computer program clima was developed to predict the time-dependent climatic change in an underground airway. The dry and wet surface temperatures of the airway used in the program were calculated following a finite difference scheme. Instead of using uniform air current temperatures in the finite difference formulations, as practised normally, the air current temperatures were regularly re-evaluated after suitable time spans so as to simulate a real situation and for improved results. The flowchart of the program is also given.

To ensure good roof control in coal longwalls, the correct handling of a shield support is of equal importance with the correct design of the support. This paper summarizes an underground survey of the performance of shield supports. The distributions of geometrical parameters as well as of parameters of support resistance were characterized by a wide scatter in the data. The effect of these parameters on the frequency of falls of ground showed a significant correlation.

Considering the attempts of some previous researchers to relate rock brittleness to the selection, design and operating efficiency of cutting machines, a study is presented to contribute to the understanding of the fundamental relationships between brittleness and the cutting efficiency of chisel picks.

Although there is not a universally accepted definition of and measurement principle for rock brittleness, in this study a more common formulation of brittleness—from compressive and tensile strength—has been adopted. Brittleness and specific energy values derived from the experimental works of various researchers were used to examine the correlations between these two parameters. The analysis of the available experimental findings indicated that the brittleness concept adopted in this work might not be a representative measure of rock cutting specific energy consumption.