In decades of research and application, success and failure in this field coexist. We
analyze these experiences and summarize them as follows:
Dense scaffolding is basically impossible.
At the early stage of research in the last century, gobside laneways were basically completed in the form of brackets. At that time, the application of various support forms had solved the coal pillar-less coal mining problems in many mining working faces. However, they are all applied to some low-gas mines without spontaneous combustion where the mining surface pressure is relatively small and the coal seam occurrence conditions are good. And the application situation is not satisfactory.
This method is rarely used due to problems such as the variety of supporting materials, heavy workload, poor support effect, and poor isolation effect of the goaf area.
The gangue stacking method should be eliminated
The gangue stacking method is a seemingly simple and economical method, but because this method cannot effectively support the roof in a timely manner, it can easily cause the roof to fall excessively. The sinking makes the tunnel unfavorable for mining work. Although this method has low material unit price, it consumes a lot of manpower and has poor isolation effect, so its adaptability is very small. The emergence of some good methods will accelerate the elimination of this method.
The masonry wall method has shortcomings
The use of prefabricated block walls can overcome many of the shortcomings of dense columns and gangue stacking mentioned in Sections 2.1 and 2.2 above, and can basically form an isolated mine. Enclosed walls in empty areas. However, this method still cannot solve the problem of the connection between the wall and the roof. It often causes excessive separation of the roof and makes the support effect poor. Improvements should be made on this basis. 2.4. Filling along the goaf with high-water materials and retaining the gob is the mainstream retaining method. Along with the working face, a tunnel filling body is constructed on the side of the goaf area to form a tunnel support belt. High-water materials can change the compressive strength of the filling body by adjusting the water-cement ratio, which can meet the engineering needs of various strength requirements. It can provide greater initial support resistance and increase resistance quickly. It can adapt to the sinking of the roof and ensure that the tunnel is smaller. It has good maintenance effect and has a high degree of mechanization. The roadside filling body constructed has good sealing performance and is effective in isolating the goaf area; the slurry made of this material does not solidify when stored alone for 24 hours, and is easy to be transported over long distances. It is very Suitable for large-scale gob-side retention.
The cast-in-situ concrete partition wall method has been proven to be better in practice
Practice in recent years has proven that although concrete walls use a large amount of valuable materials. However, this method has wide adaptability, high bearing capacity, can form sufficient capping strength, and is safe and reliable. has been widely accepted.
The disadvantages of concrete walls are that their relatively high engineering costs and construction complexity, as well as the speed of strength increase, cannot adapt to high-yield and efficient mine working faces. There are also some construction methods that cannot ensure that the wall is tightly attached to the top in time. The construction methods of this technical solution mainly include:
Large-scale self-moving gob-side lane filling bracket
This bracket greatly improves the safety of gob-side lane filling, and its structure is complex , the bracket is independent, flexible, adaptable and safe, and has good use effect.
Defect: After the construction of the concrete structure is completed, it cannot be close to the roof, causing the roof to separate from the layer and increasing the maintenance cost of the lane.
Barrel-column roadway support method
The spacing between barrels and columns is 1.4 to 1.8 meters. The number of barrel-column construction is small, which reduces the workload, the construction speed is fast, and the work surface is reduced. The impact of production ensures the normal advancement of the working surface. The number of concrete in the barrel column is 300#, the ultimate compressive strength of the specimen is 30Mpa", and the maximum support force of the concrete barrel column with a diameter of 600-660mm can reach 976OkN. However, it is inconvenient to close the goaf and the effect is worse than that of the overall concrete wall.
Paste concrete is mainly composed of Portland cement, sand and pulverized coal. Ash and paste concrete are added with additives. The special filling body has a fast solidification speed and early strength, and its maximum strength can reach 2.5 m.
The advantages of this method are. The paste form is easy to construct. The disadvantage is the incompatibility between strength and mining, which results in a much larger amount of material.
Support technology
Flexible mold support technology is developed by Wang Xiaoli of Xi'an University of Science and Technology. It was developed by a professor. It has been successfully used in more than 10 mines and is currently being promoted. The application of this technology to coal mines as filling walls is an advancement in coal mine technology. The achievement appraisal has reached the international leading level, and it enjoys a number of invention patents.
The application of this technology simplifies the construction process of cast-in-situ concrete technology for retaining roadways along the gob.
Technical evaluation of cast-in-place concrete partition walls
In the past implementation of gob-side lane retention, there were more failures than successes. Therefore, it has had side effects on the gob lane retention technology, and most people have lost confidence. Through research in recent years, people have finally realized that the mistakes in retaining roadways along the gobs in the past were mostly caused by the strength of the isolation wall and the support connection problem. In recent years, the application of cast-in-situ concrete partition walls has brought new vitality to the technology of gobside lane retention. The inherent advantages of concrete can meet engineering needs.
While concrete is an ideal method for partitioning walls, it does have some drawbacks.
The main defects in concrete construction are:
l Various brackets or formwork using steel formwork have formwork leakage, which affects the construction quality;
l It is difficult for steel formwork to solve the problem of wall roof connection, and it is easy to cause uneven gaps between the roof and the wall, and it is easy to cause excessive sinking of the roof, which greatly reduces the support effect;
l Strength of cast-in-place concrete It takes 28 days for the final strength, and any additives can only guarantee an increase in initial strength. There is no guarantee that the demand for mining dynamic pressure will be fully met under any circumstances. Therefore, the solution can only be solved by increasing the size of the concrete wall, resulting in a waste of concrete;