The effect of a multi-gob, pier-type roof structure on coal pillar load-bearing capacity and stress distribution

In order to evaluate the effect of established gob coal pillars on the stress in lower rock strata, in the context of of mining in

Jurassic coal mine in the Datong mine field, this study theoretically analysed a collapsed roof structure in gobs of Jurassic coal strata and the physics of concentrated loads on coal pillars. The collapse state of roofing in the gobs inclined with the working face and the effect of established coal pillars on the lower rock strata were obtained. Results indicated: a stabilised natural arch structure is formed in Jurassic coal strata by squeezing of collapsed upper roof blocks inclined with the working face, and the arch springing applies a highly concentrated load on the established coal pillars; affected by the established coal pillars, the upper roof of multi-gob coal pillars appears to be a pier-type structure, used as a supporting point for the upper roof load; we propose a method of calculating the stress in the lower rock strata imparted by the coal pillars. In the context of mining Jurassic coal strata at the Tongxin coal mine in the Datong mine field, the depth of the strata affected by the concentrated stress imparted by established gob coal pillars was calculated. The effective range of energy density concentration was also calculated.