residual space distribution law in long-wall old mining area

Grouting treatment in old goafs is an effective method to achieve sustainable development of mining areas after coal seam mining. Due to the concealment of the old goaf and the lack of historical information, it is difficult to directly obtain the distribution of the residual void in the old goaf. In this study, the residual void distribution law of the longwall old goaf area was studied through similar material simulation test, gangue compression test and stress arch theory. The results showed that the collapse zone can be divided into regular collapse zone and irregular collapse zone. Fissure zone and regular collapse zone have few grouting voids due to the closing effect. Due to the different forms of crushing, the irregular collapse zone has large voids and was difficult to completely close with the passage of time, which is the key area of grouting treatment. For the longwall old goaf area that has reached full mining, the stress relief zone was formed at both ends of the open-off cut and the stop-mining line, and the stress recovery zone and the stress stabilization zone were formed in turn close to the middle of the goaf area. The evolution process of stress arch and fracture arch in the stope can be divided into two stages and three periods. The first stage: the development stage of fracture arch and stress arch, that is, the stress relief and stress recovery period of broken gangue in the goaf. The second stage: the fracture arch and stress arch formation stage, that is, the stress stabilization period of broken gangue in the goaf area. On the basis of the above research, the concept of residual void equivalent height was proposed, and its calculation formula was given, and furthermore, the formula for the estimation of grouting volume was given. The height of the irregular collapse zone was 0.915~0.975 times of the coal seam mining thickness, the residual void equivalent height was about 0.3 times the mining thickness (take its upper limit value), and the residual void equivalent height in insufficiently collapsed area was 0.5 times the mining thickness.