Bottomless sublevel caving mining method ground pressure control

In order to maintain good stability of the mining approach, it is necessary to grasp the stress distribution in the rock mass around the mining approach, and the impact of the mining sequence on the approach, in order to take corresponding maintenance measures.

The finite element calculation results show that the stress distribution in the rock mass around the mining approach is shown in Figure 1 and Figure 2.

Fig.1 Stress distribution of the adjacent road roofFig.2 Stress distribution of the surrounding road

1-maximum principal stress of a section of the top plate; maximum principal stress of the 2-second sectioned roof;

Minimum principal stress of 3-stage segmented roof; minimum principal stress of 4-two segmented roof

The displacement of the rock mass on the periphery of the approach is the largest at the midpoint of the access roof, followed by the arch angle, which is gradually reduced from the arch to the wall, and the midpoint of the bottom plate is the smallest.

The Fu Shan iron ore, iron ore and Chengchao depression jade ore field measurement data shows that the route along the axial direction of recovery stress distribution and increased area reduction zone occurs (FIG. 3). The stress rise zone of Chengchao Iron Mine is 7~18m away from the working face, 10~25m in Fushan Iron Mine and 10~15m in 250m section of jadeite iron ore. The strength of the access support should meet the requirements of the stress rise value.

Fig.3 Stress distribution in the top plate along the long axis of the approachFig.4 σx distribution around the mining approach

(The dotted line in the figure is the stress distribution of the inlet roof)

The upper section is completely or not, which has a great influence on the stability of the adjacent lower section. The solid ore that has not collapsed in the upper segment constitutes a large eccentric concentrated stress in the rock mass around the lower segmental approach and produces horizontal tensile stress in the inlet roof (Fig. 4). For example, the cracks, gangs and roofing of the road spray layer of the jade iron ore and Fushan iron ore are caused by the fact that the upper section has no physical blasting.

The same segment adjacent approach mining mode has a greater influence on the stress distribution in the rock mass around the approach. The following five methods were calculated by the finite element method: parallel feeding of the approach, single-side single-entry recovery, single-entry double-sided recovery, double-entry double-sided recovery, and dual-entry single-sided recovery. The calculation results are listed in Table 1.

Table 1 Values ​​of stress distribution around the approach of different mining methods

It can be seen from the values ​​listed in Table 1 that the peripheral stress of the approach is the lowest with the parallel recovery mode of each approach. However, when this type of recovery is used to pick up the location near the contact roadway, mutual influence will occur, causing stress concentration. To this end, Fushan Iron Mine and Yushiyu Iron Mine take a certain distance ahead of the adjacent mining approach, that is, each access working surface forms a step. According to the measured results of the 250m section of the jade iron ore mine, the superimposed distance of the adjacent access working face is less than 5m, which will not cause stress superposition, which is beneficial to maintain the stability of the rock mass.