Longwall Coal Face Research Articles

長壁式採炭払における炭壁圧出型山はねの応力解析に基づく予測

The authors have developed a method called'seismic moment method' to predict microseismicity induced by deep coal mining. The method is based on stress analysis and is applied to three cases in two deep coal mines in Japan, including two cases having experiences of rockbursts.Through comparison between observation and prediction, it is clarified that the method is also effective for the three cases and that the rockbursts at longwall coal face tend to occur when microseismicity is being activated and when the width of relaxed zone in front of coal face is narrow. Criteria to evaluate rockburst danger area are also proposed.

長壁式採炭払における払面近傍の応力状態を簡便に評価し得る近似式

長壁式採炭払における払面近傍の応力状態を簡便に評価し得る近似式

Displacement discontinuities and stress changes between roof strata and their influence on longwall mining under aquifers

The results of physical model tests are analysed with special attention to the development of displacement discontinuities (bed separations) at the two stages of roof stratum movement over a longwall coal face. The relationships between roof displacement and stress concentration or relief are explored. The stress-displacement relationship is further examined by an analytical model, based on the assumption of laminated rock beams, which is used to identify possible displacement discontinuities in the roof strata which would form water inflow passages from an ovelying aquifer. Also demonstrated is the potential of the analytical model for serving as a theoretical approach or, at least, a complement to empirical methods in estimating the critical and the safe distance of mining under an aquifer.

SCALE MODEL STUDIES OF THE TRANSPORT OF AIRBORNE POLLUTANTS ON COALFACES

Studies have been carried out to investigate airflows in coalmine models, with special regard to the transport of airborne pollutants, and to examine how they relate to what happens at full-scale in an actual underground mine. If such models can be shown to provide data representative of actual mine ventilation engineering, then they can provide cost-effective alternatives to full-scale investigations. The work set out in the first instance to identify the properties of: (a) the bulk airflow and associated transport of airborne pollutants along a longwall coalface; and (b) the transport of material out of regions that were partially enclosed or poorly ventilated (e.g. in the cutting zone, in headings). For the former, an appropriate quantity is the dispersivity of the coalface airflow, for the latter the mean retention time. Both quantities may be rendered non-dimensional with respect to dimensions characteristic of the system and to velocities of the airflow. Their behaviour in relation to a third dimensionless quantity, the flow Reynolds' number is also important. Experiments were performed, using smoke or dust tracers, to investigate how these properties are interrelated and how they scale between small-scale and full-scale systems. They were carried out in a 1/10-scale laboratory model, in a full-scale surface model, and underground in an actual coalmine. The basis of most of the experiments was the 'tracer decay' method, in which the transport properties of the aerodynamic system under investigation were determined from observations of the changes in tracer concentration with time immediately following the removal of the tracer source. During these experiments, the feasibility of using small-scale models to investigate ventilation problems was clearly indicated and preliminary scaling relationships which may be used as an initial basis for predicting the transport and local build-up of pollutants in mines were developed. It is expected that applications of the ideas and methodology described will be relevant to other industries.

採炭切羽の接近・通過に伴う風道およびゲート坑道の変形について

A simple and inexpensive method is adopted to measure the gate roadway deformation with advancing longwall coal face in Ikeshima Collieries of Matsushima Coal Mining Co., Ltd.Vertical closure of the gate roadway is much greater than sides closure. It is characterized that vertical closure reaches a certain value at about 100m distance behind longwall face.The effects of strata and mining conditions on the gate roadway deformation are studied by laboratory tests and elastic numerical analysis. It is shown that the deeper the depth of coal seam is and the weaker the strength of the floor rock is, the greater the gate roadway deformation becomes.It is difficult to get an empirical equation to preestimate the gate roadway deformation by statistical treatment of measuring data because of a shortage of the precise data. It becomes clear, however, that relating the results of elastic numerical analysis presented by Everling to measuring data makes it possible to preestimate the gate roadway deformation with a considerable accuracy.

Strata deformation and support performance at a longwall coal face

Strata deformation and support performance at a longwall coal face

Induced changes in permeability of coal measure strata as an indicator of the mechanics of rock deformation above a long-wall coal face : Whitworth, K R In: Strata Mechanics (paper to the Symposium on Strata Mechanics, Newcastle upon Tyne, 5–7 April 1982)P18–24. Publ Amsterdam: Elsevier, 1982

Induced changes in permeability of coal measure strata as an indicator of the mechanics of rock deformation above a long-wall coal face : Whitworth, K R In: Strata Mechanics (paper to the Symposium on Strata Mechanics, Newcastle upon Tyne, 5–7 April 1982)P18–24. Publ Amsterdam: Elsevier, 1982

Longwall coalface roof supports for the 1980's : Morgan, D Min Engr, V141, N238, July 1981, P25–30

Longwall coalface roof supports for the 1980's : Morgan, D Min Engr, V141, N238, July 1981, P25–30

A sandbox model used to examine the stress distribution around a simulated longwall coal-face : 12F, 1T,19R. Int.J.Rock Mech.Min.Sci.V11,N8,Aug.1974,P325–335

A sandbox model used to examine the stress distribution around a simulated longwall coal-face : 12F, 1T,19R. Int.J.Rock Mech.Min.Sci.V11,N8,Aug.1974,P325–335

A sandbox model used to examine the stress distribution around a simulated longwall coal-face

A box containing sand is used to examine the possible distribution of stress in the region of coal-mine face workings; the floor of the box represents the top of a coal seam, and strips of the floor can be lowered successively through a distance equivalent to the seam thickness to represent an advancing longwall face. The effects of depth, seam thickness and two types of sand are also considered. In the model, the results show that, as the ‘face’ advances, the weight of the overlying sand is carried by a vault, the larger abutments of which are in the ‘rib-side’ areas (rib-side abutments) with smaller abutments ahead of the ‘face’ (front abutment) and behind the ‘face starting-line’. A minor arch, an abutment of which is in the ‘goaf’ (rear abutment), is thought to span the ‘face’, its span distance being a function of depth and its load a function of seam thickness, sand cohesion and depth. The traditional view postulates a plane strain condition in which the weight is carried by arching from the front to the rear of the face. The relevance of these model results to practical longwall mining conditions is discussed and some evidence is reviewed.