An analysis of the effects of sandstone channel in the roof on long wall face stability using Finite Element modeling

In the U.S., it was found that many of the reported ground control problems at longwall face were related to poor geologic conditions such as sandstone channel, faults, fold, and so on. In this study, the effects of sandstone channel on longwall face stability were evaluated using finite element models, which include a 600-ton two-leg real size shield model. It was found that, stress distribution in coal strata was greatly altered due to the existence of large-size sandstone channel in the roof. Consequently, shield loading, roof sagging, face closure, floor heave and floor punching were effected significantly as longwall face advanced toward the channel. Analysis reveals that shield leg started to yield from a certain distance (158 ft under specific condition in this study) and continued to yield until the longwall face entered low stress zone, which is below the channel body. Under this case, roof-to-floor convergence increased sharply and shield structure became unstable. Base on analysis results, a method used to determine optimum distance of longwall face from sandstone channel is proposed.