Study on disturbing influence of overlying remaining coal pillars on underlying coal seam mining

Disturbance of coal pillars in the overlying remaining section results in a change in the stress environment of the floor，while underlying working face are prone to severe mine pressure problems under the dual effects of mining disturbances and high floor stresses of the coal pillar.According to the disturbance propagation law of the coal pillar on the floor stress in the remaining section，the disturbance mechanism of coal pillar on the stresses at floor area before and after overlying coal seam was studied，and the disturbance width of remnant coal pillar area during underlying coal seam mining was calculated and analyzed.The FLAC3D numerical software was used to simulate the disturbance and damage characteristics of underlying coal seam mining under the influence of overlying remnant coal pillar.Then the influence of remnant pillar on roadway layout and the weighting of working face in underlying coal seam were analyzed and verified by field measurement and observation.The results show that the disturbance range of remnant pillar on underlying coal seam before underlying coal seam mining has a positive correlation with the width of coal pillar and the interval between the coal seams，but the influence of the inter-val between the coal seams on the disturbance range is more significant.After the mining of underlying coal seam，under the superimposition high stress of the coal pillar floor in the mining and remaining sections，along the advancing direction of underlying coal seam，the disturbance width is increased-decreased-stabilized compared with that before the mining of underlying coal seam，and the width at the peak of the advanced support pressure reaches the maximum.When the remnant coal pillar width is 20 m，the maximum disturbance width after underlying coal seam mining can be increased from 30 m to 36 m，an increase of 20%，and the disturbance angle is increased from 32° to 45°，an increase of 40.6%； and the peak value of front abutment pressure is also increased by 14.8 MPa compared with that before underlying coal seam mining.In addition，during on-site mining，the average value of the stepping distance of the underlying mining area in the remnant coal pillar was 28.3 m，which was about 38% higher than that below the gob，and the dynamic load factor was increased by 7.1%.Therefore，the roof maintenance within the disturbance range of remnant coal pillars should be strengthened to ensure the safe mining of underlying coal seam.