Numerical analysis of the time-dependent behavior of immediate roof in a hypothetical one-entry mine

This paper presents a rock mechanics investigation of the time-dependent behavior of the rock immediately surrounding the excavation in a hypothetical one-entry coal mine based on the geology of the Illinois coalfields Research in the area of time-dependency is almost nonexistent and, therefore, this research was performed to make inroads into this neglected research area. Numerical analysis of a typical one-entry coal mine in an Illinois basin was performed using the commercial finite difference program FLAC3D. The immediate roof of the coal entry was assumed to be a shale formation. Shale in other formations has shown a tendency to creep with time. Therefore, in this study the authors modeled the shale in the roof using time-dependent characteristics. The input properties were taken from laboratory creep tests performed on shale. Model runs were performed at different stages, mimicking the progressive excavation of the entry. The model results showed that stresses in the roof attained the limit of yielding. Using Mohr-Coulomb failure criteria, potential zones of failure were also predicted. The results showed that the current computational capacities are sufficient to explore this previously uncharted territory of ground control.