Isolation and clearing

I. Overview

During the mining process, the empty area often has a large distribution range. Due to various reasons (such as the different mining speed of each ore body, the mining column is not timely recovered, etc.), there are often several stages of simultaneous operation. Therefore, there are some pedestrian and transportation lanes. Or the production section is connected to the empty zone. In addition to adopting appropriate mining methods and empty area treatment methods to avoid large areas of sudden spills in the empty area, the following measures should be taken to avoid the impact of air and wave disasters: 1. Close the empty area and block all the passages leading to the production area; 2. Unblock the empty area, connect the empty area with the old empty area above the surface, and guide the impact of the air and waves to the harmless place.

The isolation and clearing of the empty area can be used as a safety measure for other empty area treatment methods (such as permanent pillar support empty area, natural collapse surrounding rock treatment empty area, etc.), and can be an independent empty area treatment method ( Abbreviated as isolation or closed method). In the latter case, after the ore is produced, the empty area is closed and allowed to exist or collapse. Obviously, this is an economical and simple method of treatment. In the past, it was considered to be only suitable for dealing with small, empty areas where the surrounding rock is very stable and scattered. Due to its outstanding advantages, many mines at home and abroad are now expanding their use. The Soviet Krivoy Rog iron mine, with the development of mining operations down, whether natural caving breakout force and can not develop to the surface so that breakouts, to form a stable natural balance of the arch, so in most cases are isolated using The method handles empty areas.

When using isolation, the following measures are generally used:

1. Closure from the empty area to all production areas;

2. Open the "skylight";

3. Leave the isolated pillar isolation space at the appropriate location;

4. Leave a bed of mineral rock of sufficient thickness to isolate the wide area from the lower production area;

5. The production area under the cushion layer adopts the “closed” mining layout, and the operations such as mining, cutting, mining and mining in the ore block are carried out under the isolation of the empty area;

6. Close monitoring of the empty area and rock cushion.

There are several types of closed types:

1. Rock blocking wall (Fig. 1a, b): In the roadway where the blocking wall needs to be constructed, the surrounding rock and the roof surrounding rock are peeled off with shallow holes or deep holes, and the roadway is filled by the loose block stones that are blasted. . Use Copper Mine copper officer medication chamber when blasting this approach, there is no blockage was found to be out of the rock phenomenon.

Figure 1 Rock blocking wall

A-peeling filling; b-blast hole blasting filling

The formation of rock blocking wall is very simple. The disadvantage is that once formed, the roadway loses its use value; with the extension of time, under the influence of blasting vibration, the loose rock will compress and form a gap in the upper part of the wall to reduce the blocking effect. Therefore, it must be checked regularly during use.

2. Concrete blocking wall. For important structures or main passages that require special protection, such as wellbore, bottoming yards, diverticulum, main transportation lanes, etc., concrete blocking walls can be used. It can effectively prevent the air impact damage caused by the huge fall of the empty area. The Tongguanshan Copper Mine is closed by a reinforced concrete blocking wave wall at the passages leading to the empty area at various stages. Considering the shock wave energy when the roof falls, the sealing thickness is generally 3m, and the wedge shape is formed. The main reinforcement of the steel bar is ø16～18mm rebar with a spacing of 200mm; the secondary reinforcement is ø6～8mm round steel with a spacing of 400mm. Each blocking wall has a 200-300mm hydrophobic hole. When the Shouwangfen copper mine closes the empty area, the section with a section larger than 6m ^{2 has} a concrete wall thickness of 2m. The reinforcement is used to increase the strength of the wall. The two sides of the roadway are also drilled with a 0.5m anchor hole and inserted into a round steel reinforcement. When the section of the roadway is less than 6m ² , the wall thickness is 1m. The Fengshan Mine in Yimen Copper Mine is a protection shaft and a main transportation roadway. In addition to the top hole filling with shallow holes, the prefabricated block wall is used to close the empty area (Fig. 2).

Figure 2 Concrete block blocking wall

3. Toothed blocking wall. When it is necessary to check the condition of the empty area regularly, a toothed blocking wall can be set (Fig. 3). The interaction between the incident wave and the reflected wave generated by the shock wave flowing through the toothed blocking wall can greatly reduce the intensity.

Figure 3 toothed blocking wall

4. Buffer type blocking wall. The buffer type blocking wall is composed of logs and sleepers with a diameter of 180 to 250 mm. During the construction, there are holes of 200-250mm between the materials (Fig. 4). The members are fixed with horse nails and wedged with the wall of the roadway. The length of the blocking wall is generally less than 3m. It can withstand the pressure created by the impact of 0.2 to 0.4 MPa.

Figure 4 buffer type blocking wall

A-sleeper buffer type blocking wall with sidewalk; b-wood buffer type blocking wall; c-wood block wall

The advantage of the buffer type blocking wall is that the structure is simple and the structure is fast. It has an opening and does not affect the ventilation of the roadway. Therefore, it is mostly used in ventilation tunnels.

    Second, the example

The No. 2~5 ore bodies in the west mining area of ​​Shizishan Copper Mine are produced in layers and like layers, buried between +40m and -210m. Because the copper content of the rock between the ore bodies is about 0.1%, the 2~5 ore bodies are combined and mined, the total thickness is 30-80m, the strike length is 250-310m, the ore body inclination is 40-60°, and the surface is 70-140m. The surface is allowed to collapse. The ore is stable and the joints are not developed. -40m or more with the vertical direction of the stage of the mining method back to the mining room, large blast back to the mining column, forming an empty area of ​​230,000 cubic meters. In view of the hard and stable surrounding rock of the roof, the joint structure is not developed, and it has the self-stabilizing condition under large span. In order to avoid the ore mining under the overburden, it is decided not to collapse the surrounding rock and continue mining under the empty area. The main measures taken are: 1 Reserve a 20m thick caving ore cushion, and the uniform ore release control layer will fall smoothly; 2. Ensure that the rock drilling working face does not communicate with the empty area; 3. The upper part of the empty area is 15×15m “skylight” straight through the surface. 4. Close the passages leading to the empty area in all production areas; 5. Using a series of methods such as deep hole foundation method of roof drilling, surface level monitoring, and borehole water level monitoring, the caving situation, empty area height and cushion position of the empty area Monitoring; 6, mining to the lower part, the empty area is further expanded, leaving a 25m wide supporting pillar in the 17 ^# line lean section, separating the large empty area into two smaller empty areas. After adopting the above measures, by the end of 1985, 2 to 5 ore bodies had safely produced 2.112 million tons of ore, and the loss and depletion were much lower than the caving method under the overburden mining (Fig. 5, Fig. 6).

Figure 5 Langshan Copper Mine Empty Area Clearing and Monitoring

1-skylight; 2-original ore body boundary line; 3-hole; 4-cracked rock; 5-ore pad

Figure 6 Nugget structure under the ore cushion

1-empty zone; 2 - ore cushion; 3-valanche overburden; 4-rock drilling approach