Prediction of upper limit position of bedding separation overlying a coal roadway within an extra-thick coal seam

Failure of the surrounding rock around a roadway induced by roof separation is one major type of underground roof-fall accidents. This failure can especially be commonly-seen in a bottom-driven roadway within an extra-thick coal seam (“bottom-driven roadway” is used throughout for ease of reference), containing weak partings in their roof coal seams. To determine the upper limit position of the roof interlayer separation is the primary premise for roof control. In this study, a mechanical model for predicting the interlayer separation overlying a bottom-driven roadway within an extra-thick coal seam was established and used to deduce the vertical stress, and length, of the elastic, and plastic zones in the rock strata above the wall of the roadway as well as the formulae for calculating the deflection in different regions of rock strata under bearing stress. Also, an approach was proposed, calculating the stratum load, deflection, and limiting span of the upper limit position of the interlayer separation in a thick coal seam. Based on the key strata control theory and its influence of bedding separation, a set of methods judging the upper limit position of the roof interlayer separation were constructed. In addition, the theoretical prediction and field monitoring for the upper limit position of interlayer separation were conducted in a typical roadway. The results obtained by these two methods are consistent, indicating that the methods proposed are conducive to improving roof control in a thick coal seam.