Influence of overburden mass behavioural properties on subsidence limit characteristics

An analytical calculation model for the angle of draw is introduced in this paper on the supposition that the roof is considered as an elastic beam. This model indicates the importance of the main factors which control the extent of subsidence produced on the surface, and also provides some appreciation of the influence of overburden strength on the angle of draw. A finite element model has been developed for application to subsidence-related rock mechanics problems. By the use of this model, the authors have investigated the effects rock mass behavioural properties on the limit angle, and also the effects of a distinct bed (strong or weak) in the overburden on the subsidence affected area at the surface. Relevant U.K. data from monitored sites for determining the three limit angles' variation with the dip of seam are discussed. The trend of the limit angle from the north of England to the Midland coalfields is also discussed in the paper. It has been found that the results from the data are in good agreement with numerical model results.