As the mining method of the caving mining method is released with the recovery, the position occupied by the overburden caving and the original ore is filled with the goaf, so the mining operation of the caving mining method has its own characteristics. (1) The pressure of the mining roadway with the bottom column collapsed and the mining method The ore with the bottom pillar caving mining method is discharged through the bottom pillar discharge tunnel. In the process of mining, often due to excessive pressure on the bottom column, the ramp is damaged and the mining work is normally carried out. Therefore, the mine pressure control of this mining method is mainly manifested in maintaining the stability of the bottom column discharge tunnel (ramp). During the recovery period, the pressure on the bottom column is different at different stages of the mining work, and can generally be divided into three stages: The first stage: after the cutting of the stop is carried out (no collapse), the upper part of the electric roadway is solid. Although there is pressure on the lower part at this time, since the unmined ore itself has a certain bearing capacity to the surrounding rock mass, the pressure at the bottom is relatively small at this time; The second stage: After the mining site collapses, the loose ore that has collapsed is accumulated in the upper part of the mine roadway, and its carrying capacity to the surrounding rock is very small. Therefore, at this time, the bottom column not only has to withstand the pressure caused by the collapse of the ore's own weight, but also withstands the pressure of the overlying collapsed rock to the bottom column, which is significantly increased compared with the first stage. The third stage: as the ore is discharged, the pressure acting on the bottom column is lowered. This is because, as the ore is discharged, the upper ore of the funnel is loosened twice, and an ellipsoidal loose space is formed in the upper part of each of the ore hoppers. The ore inside the loose ellipsoid no longer bears the load transmitted from the upper part, forming a pressure-free arch on the upper part. The loose ore load in the upper part of the arch is transmitted to the upper ore of the nearby funnel, so that during the ore-extracting process, the pressure at the center of the funnel is lowered, and a pressure-reducing zone appears. The pressure-reducing zone occurs in the range of loose ellipsoids, and the closer to the axis of the concentrating funnel, the greater the pressure drop. (2) Stress distribution in the rock mass around the approach without sublevel caving The sublevel caving method without bottom column is simpler than the bottom column caving method. The entire mining process—rock drilling, collapse, and mining—is completed in the same mining roadway (inward road). In order to maintain the stability of the mining roadway (incoming), it is necessary to understand the stress distribution in the rock mass around the approach and the influence of the mining sequence on it in order to take corresponding maintenance measures. It can be seen from Fig. 11-3 that a stress rise zone is formed in the pillars on both sides of the approach, and a stress reduction zone is formed above the roof of the roadway. Figure 11-3 Stress distribution in the rock mass around the approach Stationery Moulds,Painting Tin Metal Can Mould Die,Spray Painted Tin Metal Box Mold,Painting Acrylic Tin Can Box Molds gstarstationery , https://www.gseraser.com