Abstract

This research uses 3-D numerical analyses to analyze selected roof support plans with primary and secondary support in and around four-way coal mine intersection geometry with one corner cut-off. Rock mass engineering parameters for analyses were developed using estimated values of GSI and Hoek-Brown parameters for different roof and floor lithologies. Numerical models also included recently developed normal and shear stiffness parameters for the interfaces located in the immediate roof strata. The data shows that the currently practiced roof support geometry may not be achieving appropriate reinforcement of the rock mass around intersection corners and may contribute to roof falls. Modeled support plans are considered operationally viable and cost effective. One support plan incorporates principal author’s concepts for improved roof support around intersections. Authors also develop here an alternate approach for assessing the rock mass reinforcement effect of roof support plans using numerical modeling data. It utilizes calculating area within critical tensile, compressive, and shear strain zones before and after roof support.

1. BACKGROUND AND PROBLEM STATEMENT

Supporting intersections in room-and-pillar and longwall mining layouts is a complex engineering problem. Active and/or passive roof bolting is the most common primary support at intersections coupled with as needed inclined bolts, trusses, and cable bolts as secondary support. Even though intersections account for about 20-25% of the area mined, 70% of the roof falls in the USA with fatal and non-fatal injuries (2002 to 2007) occurred at intersections [1]. A similar study for Illinois mines for the period 2004 to 2008 revealed that 80% of roof falls occurred at intersections [2].

A few years ago numerical analyses of an idealized 4-way intersection typical in the Interior Basin longwall coal mines developed a better understanding of stress and displacement distributions around a four-way intersection [3]. That was followed by similar analyses around physically realistic irregular intersection geometries in development and setup rooms [4]. Both studies ignored bedding plane interfaces but identified that the current roof bolting patterns may not provide adequate rock mass reinforcement around the intersection corners. Numerical modeling around an intersection can identify critical areas requiring additional reinforcement. Appropriate selection and installation of primary and secondary supports around these areas may help minimize failure initiation and propagation. There is also need to develop one or more quantitative parameters that can help compare two roof support plans over a designated area. This study attempts to fill these voids in current research.

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