Research to propose calculation and application in different location options for longitudinal level under protective pillar when excavating closed coal seams

Abstract

When excavating coal seams which are close to one another, the upper’s protective pillar will cause stress concentration which is not only inside itself but also under it, those under distributed stress is uneven. There  is a high stress area under the protective pillar, if locating the mining road in this area, it will be deformed and destroyed very strongly, and very difficult to maintain stability. In addition, when excavating the upper coal seam, the integrity of the pillar rock layer is lost. It especially makes the complication in choosing the type of support structure for the mining road under protection pillar within a certain depth. This paper is based on the analysis of the formation and stress distribution rules under the protective pillar. Thereby, analyse and suggest the application conditions and reasonassble calculation formula for each location option of the longitudinal level which is under the upper’s protective pillar when excavating coal seams closed to one another.