Permanent pillar support empty zone

    I. Overview

The use of permanent pillars (or artificially constructed stone pillars) to support the roof of the empty area and to close the empty area is an empty area treatment method for mines that use gently inclined deposits (Table 1). Permanent pillars include regular, irregularly spaced pillars in the stope; top and bottom columns; panel pillars and isolated pillars reserved specifically to control rock movement. The permanent pillars are kept as far as possible in the lean or non-industrial ore belts under the conditions of meeting the requirements of recovery and empty area treatment.

Table 1 Brief description of some mines leaving permanent pillar support

The method has the advantages of simple technology, low processing cost in the empty area, and suitable for the correct retention of the pillar, and the surface can be protected in a certain period and scope. The applicable conditions are as follows:

1. Horizontally and gently tilting the ore body below the medium thickness;

2. The ore and surrounding rock are very stable, and the geological structure is weak, otherwise the proportion of the pillar is large and it is difficult to achieve the intended purpose;

3. The value and grade of the ore are low; the ore grade is unevenly distributed, and the lean or rock can be left as an ore body;

4. The size of the empty area is not large, or there is a large non-industrial ore belt, which can be divided into discrete small empty areas;

5. There are no more important buildings and structures on the surface.

When adopting this law, the next measure should be taken:

1. Carry out research work on rock mechanics, and provide basis for rational selection of retained pillars (parts, quantities, specifications) and surface movement predictions;

2. Monitoring the pillars, empty areas and surface;

3. All channels that close the empty area to the production area.

    Second, the permanent pillar support empty zone instance

Liu Jingxiang red phosphorus ore mining area coastal shallow sedimentary phosphorite deposits, to about 4200m, wherein the length of segment No. 1 North mine ore 2600m, angle 35 ~ 50 °. The average thickness of the ore body is 3.8 to 4.2 m. The ore is a dense phosphorous rock with a firmness coefficient 6=6～12, and the average grade of P ₂ O ₅ is 29.73%. The direct roof of the ore body is thick layered gray dolomite with a thickness of 10～33m and a firmness coefficient Æ’=8. ~13; Its upper part is a thin layer of argillaceous dolomite, the bottom is black shale, the firmness coefficient Æ’ = 3 ~ 5.

It is mined by the room and column method and the method of retaining ore. The stage height is 50m and the length of the ore block is 30~40m. The mining concentration has reached 100-150m, and the local reach 200m. By 1985, the goaf area was 946,200 m ² and the volume was 3.94 million m ³ , of which the mined area of ​​the northern section was 642,700 m ² and the volume was 2,559,200 m ³ . The depth is below -40m.

With the expansion of the goaf area, the ground pressure and rock movement activities are intensified, which are manifested as: deformation of the pillar, cracking until damage; roadway patching, breaking; surface cracking, small-scale collapse. Although the surface of the mine section does not need to be protected, it is not suitable to use the forced collapse roof to treat the empty area due to the single-pulse mining in the lower stage. The plan to support the empty area by leaving the permanent pillar: the lower part of the roadway along the -10m, -40m level Arranging a permanent isolation pillar with an average slope width of 20 to 25 m and a total length of about 1200 m, separating the goaf from the lower section; leaving a width of 8 to 16 m (average 10.9 m) every 140 to 160 m along the strike. A support column with an oblique length of 115 to 506 m (Fig. 1).

Figure 1 Schematic diagram of the permanent pillar support empty area

1-surface; 2-Yongliu isolation pillar; 3-wayway; 4-space zone; 5-mineral boundary

The principle of supporting the pillars:

1. Slant along the ore body to avoid false tilting;

2. Each pillar is arranged in a straight line up and down;

3. Each pillar is arranged in parallel;

4. In order to carry out long-term ground pressure observation at various stages, combined with ventilation needs, a permanent patio is arranged in the support column.

The column between the nuggets is not recovered, and the bottom column of each stage is to be recovered by 50%.

The main advantages of the program are: no need to change the current underground mining technology, simple construction, low processing costs, no impact on production, and can maintain the economic benefits of the recent enterprises. The disadvantage is that the permanent pillar mineral amount is 31.31% and the loss rate is high.