A New Model to Estimate the Convergence in Coal Mine's Galleries (Case Study: K21 Gallery of Tazareh Mine

Convergence in the galleries of underground tunnels, caused by the displacement of the ceiling, floor and walls, strongly affects the time-dependent stability of the gallery. By estimating the displacement value, the load that will be induced to the support system can be determined. By calculation of the gallery convergence caused by displacement of floor, ceiling and walls, the pressure applied on the support system can be predicted and by thus appropriate design of support system can be done. Yet, analytical and numerical models to determine the convergence of mine galleries have been presented. Nonetheless, presentation of a simple and empirical model able to predict the convergence of galleries of coal mines, far from complexities of numerical equations, can be focused by miners. In rock galleries, two kinds of instabilities often occur. In the first case, gallery instability occurs with a sudden destruction. In this case, discontinuities divide the rocks surrounding the gallery into particles and these particles can move or rotate. In the second case, instabilities often occur in very deep layers and with high initial stresses and with progressive convergence. In this paper, field studies and measurements showed that present numerical relations for prediction of final convergence, ceiling heave and wall convergence of galleries of coal mines are not applicable for convergence determination of the galleries of Tazareh Mine. Thus, a relation for more accurate estimation of galleries of Tazareh Mine, specially the gallery K21 (because of data accessibility of this gallery and similarity of geometrical-mechanical properties of this gallery to other galleries) has been presented. For this purpose, at first, effective parameters in such convergences as depth, coal layer thickness and slope, conditions of gallery floor rocks, mining time and destruction conditions were determined. In addition to parameters effective in convergence, a criterion for the estimation of the convergence value in underground coal mines galleries is presented by means of simulation of the K21 gallery of Tazareh Mine parameters. The multiple linear regression analysis was used to find the coefficients of the independent parameters by considering all effective parameters in convergence in a way that a linear relation existed between the independent and the relative parameters. The presented equation was validated by investigating the data being normal, constancy, variance and linearity of the relation between the independent and the relative parameters. A comparison between the values calculated by using the presented criteria and the real measured values in the monitoring stations showed that the presented model is highly capable of assessing of the mentioned gallery. By this empirical relation, estimation of convergence of coal galleries, in which the coal layer has different slopes, can be done.