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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
mine
Section
Ore inclination
(°)
Ore thickness
(m)
Characteristics of roof stone
Ore stability
Buried depth
(m)
Mining method
Mining method parameters
(m)
Empty area support status
Empty area
Shao Dong
Gypsum mine
7~20
13~19
Limestone, medium stable Æ’ = 6 ~ 8
Steady, Æ’=6~8
50-70
Room method
Mine room width 10 ~ 20
Mine length 30 ~ 45
The top pillar is 4m, the continuous column is 6~8m wide, and the proportion of the pillar is 40%~50%.
The roof is slightly curved and sinking, and the suburban surface is currently protected.
Pingyang Mine
Jilongshan
20~30
Average 3 to 7
Tuff , stable, ƒ=8～10
Gravel-like alum, stable, Æ’=12~15
30~40
Empty field method
Going 100 to 150 long,
Inclined from 100 to 120,
Stage high 40
Supporting the roof with irregular pillars with a spacing of 20~25m and a diameter of 5m
The empty area is 250,000 m 2 , and the surface is partially collapsed. The rest is in good condition. The surface farmer houses are protected.
Taishan Xishan
Gypsum mine
Plate kiln
Concave mining area
5~15
Average 8 to 10
Shale dolomite
More stable
60～70
Room method
The mine is 6-8 wide.
Picking height 6 to 10,
Panel length 100
The top mine is 2~3m thick, and the single column size is 6×6～8×8m.
The empty area is 400,000 m 2 , and the empty area has a long time of more than 30 years. The roof is detached, the local part is naturally degraded, the pillar is cracked, and the surface is still good.
Feldspar
Gypsum mine
Jiajiapo
5~10
Average >10
Shale class
Dolomites
More stable
Average 65
Room method
The mining area is 8 wide, the mining height is 8-10, and the length of the panel is 90-100.
The roofing mine is 3m thick and the column is 6×6～8×8m.
The empty area is 180,000 m 2 , and the existence time is 20 to 30 years. The local pillars are cracked, the roof partially falls off and the surface is still good.
The new copper smelting ore
520 ore body
420 ore body
26~55
Average 7
Average 2
Crystalline limestone, Æ’=4~6
Dolomite, limestone, stable, Æ’=3~7
Copper-bearing skarn, stable, ƒ=8～10
House column method, room column retention method
The stage height is 50-67, the length of the nugget is 40-60, the width of the column is 6, the bottom column is 5, and the top column is 2.5.
Leave a permanent column for one stage, leaving a permanent column support empty area roof at about 200m at this level.
The total volume of the empty area is 1.52 million m3 , the maximum vertical height is 250m, and the strike length is 400m. It has been in good condition for nearly 20 years.
Dangping tungsten mine
Baoshan
20~40
Average 12
Crystallized limestone, stable, Æ’=10
矽å¡å²©çŸ¿Æ’=20～21, sulfide ore Æ’=8～15
Comprehensive law, room and pillar method, comprehensive or pillar-retaining method
Stage height 40 to 51
Nugget length 50 ~ 60
In the 210,000 m 3 large empty area, there are two permanent pillars of 5 m and 10-12 m along the long axis, and the others are irregular pillars.
The total volume of the empty area is 420,000 m 3 , which is in good condition and partially collapsed near the surface.
Sinko mercury mine
Hotel
15~25
3 to 9 parts
Up to 18
Sputum dolomite, Æ’ = 8 ~ 10, partial Æ’ = 10 ~ 14
Steady, Æ’=8~10
240
Comprehensive law
The nugget is 40~50 wide and slant length 32
The top and bottom columns are 3 meters wide, leaving 3 meters of irregular ore pillars and artificial rock pillars to support the roof of the empty area. The proportion of pillar reserves is 8% to 12%.
The old airspace has been exposed for 100 years and is in good condition.
Tongren mercury mine
Lu La
5~10
a few meters to
More than 10 meters
Steady, Æ’=8~10
Steady, Æ’=8~12
150
Comprehensive law
Nugget area 30×40
15 to 20 meters spacing, ø4m pillar and artificial rock pillar support empty area roof
The empty area has been maintained for more than 20 years without collapse
Guizhou mercury mine
Foot punch
Slow tilt
0.3 to 4 to
5~10
Mud dolomite, Æ’=10
100
Comprehensive law, room method
Ø2～6m irregular pillar support empty area roof
The area of ​​the goaf is 50,000 m 2 and the volume is 340,000 m 3 . The maintenance of the empty area is good for more than 20 years.
Guizhou mercury mine
Wanshan
3~17
0.5 to 30
Dolomite limestone, ƒ=8～10
ƒ=10～12, a few ƒ=16
55～340
Room method
Mine length 30, width 8-12
Irregular pillar support aerial roof, the proportion of pillar reserves is 5% to 6%
The goaf is up to 30m, and some old empty areas are 500-600m 2 . The roof rarely lands naturally.
Barry tin mine
20~30
0.5 to 8
Thick layered limestone, stable, ƒ=8～12 矽 shale, ƒ=12～15
Steady and medium stability
200
Comprehensive law
The stage height is 20, the length of the nugget is 50-60, the width of the top column is 1.2-2, and the width of the bottom column is 3.
Ø2～3m permanent pillar support roof
5 years after the mining of individual ore blocks, the roof of the empty area collapsed
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 ƒ=8. ~13; Its upper part is a thin layer of argillaceous dolomite, the bottom is black shale, the firmness coefficient ƒ = 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.