Analytical Modeling of Coal Mine Roof Behavior: Fid-Bau Portal

Analytical Modeling of Coal Mine Roof Behavior

R. T. Langland

A comprehensive series of three-dimensional, finite-element calculations of roof behavior at three different sites in a room-and-pillar coal mine have been performed. The calculated results have been compared with experimental results obtained in an extensive in situ field measurement program. The parameters studied were roof sag (relative displacement between roof strata), roof-bolt load change, and roof-to-floor convergence. The study included a wide range of extraction ratios (27 to 80%). A series of parametric studies were performed for one of the sites, including: changing the viscoelastic time parameter; varying the preload on the bolts; and changing the effective stiffness of the bolts. The good agreement between analysis and field experiments shows that three-dimensional, finite-element modeling of mining can be an extremely useful tool for understanding mine behavior. Some general conclusions reached on the basis of the analysis are: significant movement occurs in the rock mass during excavation (all finite-element modeling should include excavation to get reliable results); accurate geometry and accurate material properties are essential; roof-bolt anchor movement determines a bolt's effective stiffness and, consequently, the amount of load change a bolt will experience; movement of the rock as a continuum is not influenced by the bolts (they merely follow the deformation of the rock mass); the cause of convergence could not be determined (pillar softening, floor heave, or a combination of the two might be responsible); the roof sag and bolt-load change showed no long-term, time-dependent behavior; and the convergence rate between the floor and the roof was highest immediately after excavation. (After approximately 30 days, a steady rate, equal to about one-third of the original convergence rate, was achieved). (ERA citation 04:052521)