Permanent pillar support empty zone

Â Â Â 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 (Â°)	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, Æ’=8ï½ž10	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	60ï½ž70	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 6Ã—6ï½ž8Ã—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 6Ã—6ï½ž8Ã—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, Æ’=8ï½ž10		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	çŸ½å¡å²©çŸ¿Æ’=20ï½ž21, sulfide ore Æ’=8ï½ž15		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 30Ã—40	15 to 20 meters spacing, Ã¸4m 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		Ã˜2ï½ž6m irregular pillar support empty area roof	The area of â€‹â€‹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, Æ’=8ï½ž10	Æ’=10ï½ž12, a few Æ’=16	55ï½ž340	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, Æ’=8ï½ž12 çŸ½ shale, Æ’=12ï½ž15	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.	Ã˜2ï½ž3m 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.

Â Â Â 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 Â°. 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=6ï½ž12, 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 10ï½ž33m 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 â€‹â€‹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.

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