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How Coal is Mined
Published in H. Townshend-Rose, The British Coal Industry, 2017
The subsidence which takes place in the mine eventually affects the overlying surface land, with consequences that may be serious. Unless preventive action is taken, subsidence at the surface amounts to about one-half of the thickness of coal removed, and will extend to a distance beyond the vertical line above the working face equal to about a quarter of the depth of the seam being worked. In the area ‘let down’, drainage systems of agricultural land may be destroyed, highways and public service pipes fractured, and surface buildings suffer anything from a few cracks to complete destruction; it does not, however, necessarily follow that extensive damage will be caused. Land not immediately above the underground workings may be affected by what is known as ‘draw’; that is, the tendency for strata to be drawn in towards the point of subsidence. Damage resulting from subsidence can be considerably reduced by adopting suitable mining methods. The longwall system of mining which advances fairly rapidly on a broad front causes less surface damage than is the case with the room and pillar system of working. Where solid stowing is economically possible the extent of subsi¬dence damage is further reduced. In addition, structural precautions can be taken in surface building in a mining area so as to prevent or minimize damage from the workings. Pillars of coal may be left for the support of buildings of historic, aesthetic or industrial importance, or which provide some essential service, but these pillars have the disadvantage of causing distortion at the junction of the supported and unsupported surface land.
Navigating without vision: spontaneous use of terrain slant in outdoor place learning
Published in Spatial Cognition & Computation, 2021
Daniele Nardi, Katelyn J. Singer, Krista M. Price, Samantha E. Carpenter, Joseph A. Bryant, Mackenzie A. Hatheway, Jada N. Johnson, Annika K. Pairitz, Keldyn L. Young, Nora S. Newcombe
Without taking off the blindfold, the participant was given a hand compass and allowed to practice pointing with it. They were told that they would be asked questions and to point to an object with the compass. They had to hold the compass with one hand and extend the whole arm when pointing. The experimenter also said that there was no time limit, but they would be timed. The first question was: “Is the ground slanted or horizontal?”. Timing started at the end of the question and ended as soon as the participant responded. If the participant answered “slanted”, they were told: “Now please indicate the uphill direction by pointing with the compass, and say done when you are sure”. Timing started at the end of the question and ended when they said done. The absolute (unsigned) angular error between the pointing direction and the correct uphill direction was calculated. The slope identification task was carried out only at the second site in order to not draw attention to the terrain.
Stochastic optimisation of long-term block cave scheduling with hang-up and grade uncertainty
Published in International Journal of Mining, Reclamation and Environment, 2019
Rein Dirkx, Vassilios Kazakidis, Roussos Dimitrakopoulos
The objective function in Equation (1) maximises the NPV and at the same time minimises deviations from targets. Three types of deviations are considered. First are the deviations from the mill tonnage target. Second, the grade deviation to control the influence of the grade uncertainty. Finally, the time deviation, the main contribution of this model, to control the influence of the delays from hang-ups. The penalty costs for the deviations (denoted by in Equation (1)) are discounted in terms of geological risk discounting (GRD), as introduced by Dimitrakopoulos and Ramazan [33]. GRD allows to control risk in meeting production targets; more specifically, it minimises deviations in early production years and defers risk (of not meeting production targets) to later periods when more information will become available. The objective function shows the value calculation on a block basis with a fixed recovery. This is a simplification required to keep the model linear such that it is solvable using commercially available optimisers. To make the notation shorter and simpler, it is assumed that for all draw points. The opening of draw points is modelled as an ‘opened-by’ variable as proposed by Caccetta and Hill [34] for the open-pit mining context. This formulation has been proved to be stronger than the more intuitive ‘opened-in’ formulation.
GreenValve: hydrodynamics and applications of the control valve for energy harvesting
Published in Urban Water Journal, 2018
Stefano Malavasi, Marco Maria Agostino Rossi, Giacomo Ferrarese
Using these parameters it is possible to draw a hill plot that describes the performances of the valve in many different conditions of differential pressure, dimension and velocity of the flow. In Figure 6 is shown the plot of the efficiency as a function of the speed factor and the discharge factor. The contour is plotted on the basis of the experimental points, shown on the plot. For nED equal to zero, the efficiency has been set to zero and the same condition is imposed for QED equal to zero. It must be noted that the working conditions of the application cases presented in the paragraph Estimated potential of two real cases are all included in the range of experimental points showed in Figure 6.