Application of foamed concrete in mines

Due to its light weight, good thermal insulation and thermal insulation properties, as well as its functions of earthquake resistance, energy absorption and noise reduction, foamed concrete materials are currently used in many fields such as domestic construction, floor heating, and gardening. The application of foamed concrete in coal mines in my country has just started, but it shows good momentum. In the near future, foamed concrete will be used as mine backfill materials, support materials and water blocking materials.

1 Backfilling Materials

1 Backfilling of Goaf Areas

Our country is a large coal production and consumption country. However, long-term coal mining has formed large-scale subsidence areas. According to incomplete statistics, by 2005, the subsidence area nationwide had reached 700,000 hectares. Mining subsidence has led to the abandonment of a large amount of farmland and the destruction of surface water systems, causing serious ecological disasters. Backfilling the goaf is the most direct and effective method to cure surface subsidence and mining damage. Backfilling of coal mine goafs is a worldwide problem. For a long time, the main technologies used at home and abroad include dry filling, water-sand filling and cement filling. The cemented backfill mining method is mostly used in metal mines. Generally, gravel, river sand or tailings are used as aggregates, mixed with cement or lime cementing materials to form a slurry or paste, and then transported to the filling area by pipeline pumping or gravity flow. Compared with water-sand filling, cemented filling materials have greater strength after cementation and can be used for medium-thick ore bodies with deep burial depth, high ground pressure, and unstable surrounding rocks. The use of cemented filling has become an inevitable trend for backfilling in coal mine goafs. In recent years, our country has successfully tested and popularized new technologies such as high-concentration cement filling and high-water rapid-setting full-water solidification cement filling.

The cement used in traditional cement-bonded concrete filling materials is generally 42.5 ordinary Portland cement, the dosage is 150~300kg/m3, the water-cement ratio is about 1.2~1.3, and the 28d concrete compressive strength is 5.0~10.0MPa , cement accounts for 30 to 60% of the cement filling cost. Generally, the cost per ton of coal will increase by about 40 yuan/ton. Reducing cement consumption and cost is an effective way to find new filling materials suitable for mines. Foamed concrete is easy to transport, has good fluidity and is cheap. It can maintain a certain strength by mixing tailings powder and cement of different grades. It can be used as a new type of filling body to backfill in coal mine goafs. used in.

2 Filling of caving voids

After the roof of the mining working surface collapses, a cavity of a certain range and height will be formed. If it is not processed and filled in time, the support body will not be able to perform its functions. The supporting effect may cause a wider range of roof accidents and economic losses, and may also cause gas accumulation.

The traditional method of dealing with these roof voids is to manually build wooden stacks or use polyurethane materials to chemically reinforce them. The construction speed of wood stacks is slow, the material consumption is high, the contact surface between the wood stacks and the roof is small, the control effect is poor, and the operation is very dangerous. Chemical reinforcement has disadvantages such as high cost and easy heat and fire. These shortcomings can be overcome by filling the roof cavity with foamed concrete. By adjusting the foaming multiple and changing the water-cement ratio, the compressive strength of foamed concrete can be adjusted to a maximum of about 13MPa. When the material reaches its yield limit under unidirectional compression, the material can still maintain a high load-bearing capacity as the deformation increases. Because the material structure is closed-cell, it has good air tightness. This method of using foam cement to fill caving cavities can mechanize the work of dealing with roof caving cavities, and the construction is safe and fast. It can increase the support for the cavity wall, prevent the roof caving range from continuing to expand, and improve the interaction between the bracket and the surrounding rock. , and can prevent the accumulation of harmful gases in the cavity and prevent fires. It is a new technology with many advantages.

1-Foam cement 2-Filling pipe 3-Woven cord 4-Overhead beam 5 Anchor rod 6-Baffle 7-Plastic woven bag

2. Mine support

Concrete has always been used for cast-in-situ walls in underground tunnel projects such as shaft shafts, shaft bottom yards, various cave chambers, and tunnels that are not affected by mining. Rigid cast-in-situ concrete only produces elastic deformation under the pressure of surrounding rock, and failure is more common when it withstands large rigid displacements.

Because foam concrete has certain flexibility, high compressibility, and certain strength, it can be used as the following support forms for mines:

1 As The collapsible supporting cushion layer

reduces and moderates the stress on the support, keeps the support evenly loaded, and can effectively release the initial elastic deformation energy of the surrounding rock. The specific structure is shown in Figure 4.

2 Made into foamed concrete blocks, used for roadway masonry and immediate support

Used to build load-bearing walls and ventilated sealed walls. In recent years, foamed concrete has been used The ventilation and sealing work of building block construction has been promoted and applied in many mines in my country. Due to its good shrinkability and superior overall sealing performance, it has been unanimously praised by on-site engineering and technical personnel.

3 Can-type piers

A foam concrete bracket called Can has been used in the United States, Australia and other countries for more than 10 years. In recent years, this pier has It has already been used in our country. In March 2009, Shanxi Meidaning Coal Mine introduced a batch of piers from Australia. The piers were produced by the Australian Hanson burrel company, with a maximum load of 200 tons. The pier was scientifically tested in the 402 air dynamic pressure tunnel along the underground dual-measurement mining in Daning Mine.��, the test achieved satisfactory results. By comparing with the wood stack, the maximum bearing capacity of the wood stack was 33.6 tons, and the average bearing capacity was 28.48 tons; while the maximum bearing capacity of the piers was 125.6 tons, and the average bearing capacity was 75.75 tons. , which are 3.75 times and 2.66 times that of the wood stack respectively. Judging from the surface displacement of the roadway, in the area supported by wooden piles, the average movement of the roof and bottom is 221.6mm, and the average movement of the two gangs is 154.5mm. In the area supported by piers, the average movement of the roof and bottom is 221.6mm. The moving amount is 85.37mm, and the average moving amount of the two gangs is 34.2mm, which is 38.5% and 22.1% of the wooden stack respectively. The support efficiency of piers is 3-5 times that of ordinary wooden stacks.

With the increase in the span of coal mine tunnels in my country and the optimization of the mining system, tank-type piers will be used in dynamic pressure tunnels, long-span cutting tunnels, shutdown maintenance, tile row tunnels, narrow coal pillar tunnels, etc. It has been further applied in the support of soft rock and dynamic pressure tunnels such as gob-side tunnels.

3. Grouting and water blocking

Grouting and water blocking is an important technology for mine water prevention and control. At present, most coal mine tunnel water blocking grouting materials use cement slurry or cement-water glass slurry. Its main advantages are low cost and wide source of materials. However, it is easy to shrink after hardening and produce small cracks. The cracks gradually expand under hydraulic erosion, and the water blocking effect is not ideal. Foamed concrete is used as the water blocking material. Since it is not affected by shrinkage deformation, the closed-cell structure can effectively absorb shrinkage deformation and increase the water flow path to achieve the purpose of water stop. The use of foam cement to plug water in Shengli Oilfield has achieved certain results, with an average validity period of 12.5 months.

IV. Conclusion

Foamed concrete has a production history of several decades in my country, but it has been mainly used in the construction industry and has not been widely used in the coal mine field. In the future, it is necessary to strengthen research and development work on foam materials, construction technology and construction equipment to adapt to the use requirements of my country's mines and play a greater role in the safe and efficient production of my country's mines.

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