Study on ground pressure control of effective simultaneous production in close distance coal seams

No.3 and No.4 coal seams in Nanyangpo mine are main mining coal seams with distances from 23m to 26m, and No.4 coal seam (lower) mining influenced by No.3 coal seam(upper) mining failure, and this is simultaneous mining of medium-thickness(No.3) and high-thickness(No.4) coal seam in short distance. Based on physical and mechanical tests, on-line stress monitoring, support load non-destructive testing and numerical computation, it was showed that distribution law of lateral stress in monitoring area, carrying angle of lower coal seam is 45° and carrying angle in significant abutment pressure increase region is 31°for No.3 coal seam mining. The supporting effects of along gob area of 30205 transportation drift and 4105 transportation drift were monitored and evaluated. Four reasons of serious deformation of along gob roadway in lower coal seam were analyzed. The size of section coal pillar at return air-way of next non-mining section face 4107 and the reasonable distance of lower coal seam lagging behind upper coal seam under normal conditions were determined. The research results will contribute to reasonable mining design and choice of supporting parameters, and realize effective simultaneous mining of medium-thickness and high-thickness coal seam in short distance.