The definition of Ultra-close multiple seams as defined by the floor disturbance depth, h_σ due to mining in the upper seam is proposed: it refers to those coal seams that are spaced very closely, i.e. h_l, the distance between seams, is small or equal to h_σ , and mining of any one of the seams will significantly affect the others. Those seams are called the ultra-close multiple seam group. Theoretical formula for defining it and practical examples are given in this paper Underground measurements and numerical analysis show that in ultra-close multiple seam mining, the characteristics of ground pressure due to lower seam mining is different torn that of single seam mining. The major differences is that the roof, as a result of damaged caused by the upper seam mining, is full of factures; the roof broke up in the belt entry and fell down easily; support loading at the face was small without clear periodic weighting phenomenon Based on these results the roof structure model and roof control theory for ultra-close multiple-seam are established.
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