Measurement and analysis of the roof pressure on hydraulic props in longwall

This paper presents a study of the support system employed in several workings in the coalfields of Castile-Leon in Northern Spain. The mining method employed is the longwall coal face, in which caving is controlled by means of individual hydraulic props. We first report the empirical formulas used to estimate the roof pressure in mines of this type. We also analyze the constraints imposed in the Dortmund guidelines for the mining of longwall coal faces. Subsequently, we present the methodology and equipment designed to measure "in situ" the pressures that the roof exerts on the hydraulic props. These measurements were carried out at twelve workings in the Castile-Leon coalfields. A detailed description of two of these workings is provided (called Seam 24 and the Wide Seam), in which pressure measurements were taken simultaneously in several rows of props, analyzing these as a function of the mining phases of the working. On the basis of the measured values, a new empirical formula is proposed for determining the roof pressure that the props must support, which fits the type of studied longwall workings. The data suggest that the Dortmund guidelines are too conservative for the Castile-Leon coalfield and that adoption into the ITC (in English, Complementary Technical Instructions) would place several working that for years have been mined under safe conditions outside the regulations. (C) 2008 Elsevier B.V. All rights reserved.