| In recent years, longwall mining has become increasingly important to maintaining a healthy coal mining industry. Although proper pillar design is essential to the safety and productivity of longwall faces, no satisfactory longwall pillar design method is currently available. This dissertation proposes a new method for longwall pillar design, developed primarily from underground measurements.; The research described in this dissertation addressed three areas of direct relevance to longwall pillar design: (1) The magnitude, time-of-arrival, and distribution of the abutment loads applied to longwall pillars; (2) The strength and behavior of coal pillars; (3) The relationship between pillar sizing and entry stability, and other factors affecting the roof/pillar/floor interaction during longwall mining. The research focussed on two field studies performed in adjacent longwall panels at a West Virginia coal mine. In each study, measurements of pillar stress, pillar deformation, and entry stability were obtained during and after the approach of the longwall face. Other research included detailed re-analyses of field data from other studies, an in-depth comparative study of available longwall pillar design methods, numerical modeling to determine post-development longwall pillar loads, and an evaluation of two index tests used to determine coal strength.; The proposed longwall pillar design method incorporates a new approach to estimating abutment loads that was developed from the research. The method also employs existing empirical pillar strength formulas that were shown to be applicable to longwall pillars. The proposed design method represents an improvement over the existing methods, because it can be used with designs employing combinations of differently sized pillars, and because it can calculate stability factors for the several different service functions of pillars around a longwall. The method is also easy to use. Application to case histories indicates that the proposed method provides useful results for many areas of the Appalachian coal fields. |
