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To ensure the safety of excavation of carbonic coal strata in Datong minefields, the effect of multi-gob roof structure after the excavation of upper Jurassic close distance coal strata needs to be analysed. The multi-gob roof structure of Jurassic close distance and its effect was evaluated by theoretical analysis in this study. The types of multi-gob roof structure of close distance coal strata were categorised and the stress distribution in each type of structure was analysed. Results showed that: the blocks of the upper roofing of the gobs of Jurassic coal strata in the inclined direction of the working face extrude with each other, resulting in stable natural arch structure. The arch springing acts on the coal pillars in the gobs, resulting in significant concentrated load; according to the location of reservation of coal pillars in the gobs and spacing of coal strata, the roof structure of the gobs of close distance coal strata can be categorised into four types. Calculating equations of the load of coal pillars and waste rocks in the gobs for each type of structure were proposed; with respect to the condition of production of upper Jurassic coal strata in Tongxin coal mines, the multi-gob roofing of the coal strata of the mine was determined as aligned coupled structure and the effective depth of coal pillars in the gobs of the respective roof structure was calculated. Results from this study provide basis for the prediction and forecast of the mine pressure on the working face of underneath carbonic coal strata as well as the analysis of pressure strength. ARTICLE INFO

Roof structure of close distance coal strata in multi-gob condition and its effects