Interaction Mechanism of the Upper and Lower Main Roofs with Different Properties in Close Coal Seams: A Case Study

Close-distance coal seams are widely distributed in China, and the mining of overlying leads to floor damage. To grasp properties fracture spans damaged main roof underlying seam, combining calculation damage depth with rock theory formulas for calculating first periodic weighting intervals instability conditions key blocks obtained. Three interaction stability mechanics models proposed different upper lower roof, obtained when lines overlap. When combined a specific example, field monitoring verified results. The research results as follows: (1) intervals, horizontal thrust between blocks, critical load significantly reduced. Still, there differences its reduction under loads, rotation angles, lumpiness. (2) roofs overlap, is lowest. There three linkage regions curves two blocks. (3) In this case, equivalent 0.397, which belongs local type. Its 40 m 16 m, 22% 24% less than no (4) A supporting 0.489 MPa required maintain block, block prone rotary sliding during weighting, respectively. Thus, supports need bear total 0.988 0.761 simultaneously. ground pressure data monitored on-site accord