3rd North American Rock Mechanics Symposium, Cancun, Mexico, 3–5 June 1998
Authors: L. J. Gilbride, A. M. Richardson, and J. F. T. Agapito (AAI)

Simplified design methods based on statics have traditionally been used for determining the capacity of longwall shield supports. However, these methods are mechanically oversimplified in the statically indeterminate loading environment at the longwall face. Computer block models, which have found many applications in rock mechanics in recent years, are ideally suited to analyzing the mechanics of shield loading, but have not yet been widely applied to this problem. In this paper the topic of using block models to determine longwall shield capacity is addressed. Agapito Associates, Inc. (AAI) has performed these analyses for major coal and trona projects in the past several years. Block analysis has proven to be a useful supplement to traditional methods in determining support capacities, especially under special loading conditions such as superincumbent loading by massive sandstones that are nearly impossible to analyze traditionally. Applications of the block model and examples of its uses from project case histories are selected to illustrate the mechanics of shield loading. Although assumptions are required in all types of modeling, this method provides an accurate, mechanically correct framework for analysis. This enables a clearer definition of the sensitivity of the problem to the assumed parameters that can be achieved using simplified analysis. Specific data needed to calibrate block models and improve the reliability of support prediction are outlined.

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