Abstract
The Bureau of Mines has developed a unique new mine design procedure to detemine the changing static load distributions imposed on underground support structures during the mining cycle. The procedure reduces the complexities associated with analyzing a three- dimensional problem. A combination of the multiple-seam displacement-discontinuity model and a two-dimensional finite- element window model produces refined results for a specific area of interest by assuming displacement compatability between models. Input to the procedure includes the geometry of mined-out areas in up to two adjacent seams, the rock mass characteristics of the surrounding geology, the in situ stress conditions, and the mining sequence. The displacement-discontinuity program calculates expected loadings for mine structures affected by the mining cycle and/or overlying or underlying seams. Pseudoelastic finite-element analysis using a yield-factor approach determines the stability of coal pillars by simulating the degree and extent of progressive rib failure and subsequent load transfer. Application of the procedure is demonstrated on a field problem. Induced stress changes predicted from the numerical model analysis are in reasonably good agreement with stress measurements obtained from an instrumented chain pillar affected by remnant workings in an upper seam.
