The coal mining under the water body mainly prevents the water or mud sand in the overlying water body from falling into the well, thereby increasing the risk of underground coal mining and the drainage cost. Over the years, China's water mining has liberated a large number of underwater coal resources, and gained a wealth of experience, forming a theoretical system with China's characteristics.
The mining method under the water body is deep and shallow, first and then near, first adopting the location of thick water-sparing layer and the location of the later-collecting water-sparing layer, the principle of adopting good conditions and complex mining conditions. The coal mining method generally has a single long-walled, inclined layered artificial false-top longwall, a warehouse type, and a pseudo-tilt flexible shield bracket that is urged along the strike direction. The implementation of fully mechanized caving in the water body began in the early 1990s, and the application is relatively common. In the mining areas such as Zhangzhou, Xingtai, Longkou, Datun and Huainan, waterproofing is provided for different water-rich loose aquifers and different types of overburden. Under the conditions of sand control and explosion-proof coal pillars, the fully mechanized caving safety mining has been successfully realized. The roof management generally has all the spans, water sand filling, vermiculite filling and coal pillar support roof.
1.2 Top coal mining under water
The use of top coal mining technology under water body has made great changes in the activity law and structural characteristics of the overlying strata in the stope, resulting in obvious mine pressure. Due to the use of fully mechanized caving mining under water to increase the thickness of coal mining, the mining intensity will also increase, and the degree of destructive impact of mining will obviously increase the impact on safe coal mining under water. Specific technical measures should be taken. The amount of water inflow at the working surface is controlled at a level that guarantees safe production and at the same time achieves good economic benefits, thereby maximizing the mining of coal under water.
The production efficiency of top coal mining depends on whether the top coal caving is sufficient and whether the top coal can be smoothly discharged. Under the condition that the top coal caving is better, the top coal mining rate and top coal caving effect It depends on the determination of the reasonable top coal process parameters. The influence of the top coal release law on the bending zone, the fracture zone and the fracture zone during coal mining under water is determined, especially the impact on the fracture zone.
For coal stope top down, due to mining conditions, coal generally horizontal top and vertical displacement along the direction perpendicular to the lead occurred, resulting in displacement of the top coal breakage and crushing to smaller inclination angle The longwall top coal caving face is mainly characterized by horizontal displacement. The old roof is located in the top of the direct or directly in the hard rock layer above the coal seam, can maintain a large area of â€‹â€‹the suspension, generally does not fall. Due to the use of top coal in the water, higher requirements are placed on the topping.
Under the conditions of top coal mining, the possible caving thickness of the direct roof is still a multiple of the thickness of the primary mining. The value is about 1.9 to 2.5 times under the general mining conditions. The results are confirmed by the actual measurement research of the top coal mining in China. At present, a large number of studies have been carried out on the law of overburden failure caused by layered mining of thin or thick coal seams (primary mining height of 3 m), and the prediction of mining under different overburden conditions (hard, medium hard and weak rock formations) is proposed. The formula for the maximum height of the rock spanning zone and the water-conducting fracture zone, which scientifically guides the mining under water. Due to the large thickness of the fully mechanized caving mining, the movement and damage of the surface and overburden are more severe, and the height of the sloping belt and the water-conducting crack zone is higher than that of other coal mining methods. Nowadays, there is a lack of understanding of the law of overburden damage in fully mechanized caving mining. China's "Three Under" Mining Regulations has made clear technical regulations on the thickness of different types of water bodies, the safety coal pillars to be retained, and gives a single coal seam longwall mining that guides safe coal mining under water bodies. And the calculation formula of overburden caving zone and water guiding fissure zone in ordinary layer mining of extra-thick coal seam. However, due to the numerous geological factors affecting the damage of overlying strata, the mining conditions of each working face are complicated. Especially under the conditions that there is not enough data at home and abroad to unify the surface failure law of fully mechanized caving mining, the existing experience and regulations cannot Promoted in coal mining under water.
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