Management and prevention of broken roof

1.0 Mechanism and law of roof collapse of broken roof

The broken roof occurs mostly in fault zones, folds, joints and cracks in the old alleys. Due to the existence of the above geological structures, the roof subsidence and joint fissures are more serious, and the rock blocks are very broken, mainly in the top coal. Or the top plate is low in strength, and it is easy to break and break under the action of mine pressure. Sometimes the top plate appears as a broken piece of several meters in diameter, even powdery.

1.1 During the process of geological change, the rock layer is pulled or squeezed, and the rock layer is cut to form a fault, which destroys the integrity of the roof, so that the cracks in the roof near the fracture surface develop and break, and the fault layer is filled with powder. Or mud, the fault plane is relatively smooth, so that the rock between the upper and lower discs has no cohesive force, especially when the fault plane becomes a water-conducting fissure, it is separated from each other and the tectonic stress and residual stress change the stress field of the original rock. The distribution and the magnitude of the stress, therefore, local topping is prone to occur near the fault, and the initial topping, initial pressure, and periodic pressure step are changed, which makes the roof management lose its regularity.

1.2 Due to crustal movement, the formation rock can no longer withstand horizontal pressure and fold, so that the tectonic stress and residual stress in the fold affect the distribution of the stress field and the stress of the original rock layer, and it is easy to gather a large amount in the anticline and the oblique direction. The elastic energy. In particular, when the small folds are affected by the mining, the top plate is partially broken, and the broken rock is easy to push down the bracket, causing local roofing.

1.3 Due to the influence of the compression of the coal seam, the extruded coal and rock layers are thinned, and many joints and crack sliding surfaces are formed after the top plate is pressed, so that the roof is mostly broken and the working surface is passing through the broken surface. It is easy to cause local roofing. Due to the influence of the original or tectonic, there are a large number of joints and fissures in the coal and rock layers. These joints and fissures cause the roof to form separate and isolated blocks of the shape of "herringbone", "straw hat flower" and "pot bottom stone". Because of its isolation and isolation, it is easy to fall off and cause local roofing, and sometimes even push the bracket down, causing a large roof. The original or structural fissures may cause different roofing accidents due to the different positional relationship with the working surface, mainly due to the difference in the relationship between the joint fissure surface and the working surface line, resulting in the umbrella, probe coal, roof sinking, horizontal movement, and step shift. Especially in the case where the roof has an aquifer or water in the old pond, the inclined crack of the inclined coal seam increases the water in the mining space, which reduces the rock strength of the direct roof, which causes the working face to help, local roofing, and even a large area. Pushing down the roof of the shed.

2.0 Measures taken for the management of broken roof

The main feature of the broken roof is its fracture. The broken roof allows for a shorter exposure time and a small exposed area. If the timely support is not available, the roof leakage accident is likely to occur. If the timely and effective control is not obtained, the leakage roof range becomes larger and larger, resulting in a large roof accident. In order to prevent the leakage of the broken roof, it is necessary to properly control the roof before it occurs locally, so that it does not form a weak link or seal it in time after the local leakage occurs, strengthen the support and limit the local leakage. The area has further expanded. To this end, according to the law of the topping mechanism of the broken roof, to prevent the occurrence of local roofing accidents, it is necessary to take targeted measures.

2.1 Strengthen production geological work. Detailed geological specifications must be provided before the working face is recovered, including geological structure changes, fault occurrence, fold and fracture zone, joint fissures and water.

The actual nature of the case 2.2 mining area technicians and engineers in charge of the recovery process, we must grasp the face of faults, folds small structure, the top of the slate, broken belt, predict possible roof collapse in scope, nature, and to develop practical And targeted measures.

2.3 Strengthen employee training and education so that employees fully recognize the harm of local roofing and the importance of strengthening project quality. It is required to do a very fine job. The main types of workers, such as mining, support, and returning, should repeatedly educate the local topping mechanism. It is necessary to summarize the experience of preventing local roofing and minimize the occurrence of local roofing accidents.

2.4 Strengthen cycle progress and operation process management. The working surface of the single-pillar strut, due to the small support resistance and the large amount of the top and bottom plates, there is a significant difference in the top plate breaking condition of 2 meters and 2 days into 1 meter in the working face of our mine, as long as it reaches 2 meters per day. , the roof condition is greatly improved, and the integrity of the roof is ensured. In the operation process, it is ensured that the coal falling and the topping are not carried out at the same time, so as to prevent local roofing caused by the simultaneous topping and falling coal.

2.5 The mosaic roof of the joint development of the joints mostly occurs on the side of the coal wall. Most of the time is after the shot, in the empty roof stage where the permanent support has not been established. Therefore, the mine uses the method of leading the hanging beam and the early test board to shorten the beam end. The distance to the coal wall to control local roofing.

2.6 Timely advance support, inserting the back to deal with the local empty roof (empty) to prevent roofing and pumping. When the roof is broken due to the broken roof and loose roof, it is necessary to set up the raft in the empty roof area in time. .

2.7 Strengthen the support of small fault zones with small drop. When the mine is working on site, the fault is obliquely intersected with the working face, the contact surface between the fault and the working face is minimized, and the method of partial fault crossing is adopted; and the extended top control and dense backing are adopted at the local over-fault, and the quality reaches “ The method of “stable”, “tight”, “average” and “qi”; after the step of increasing the top step, the pillars at the fault are recovered again; the coal is shot down to take shallow eyes, less charge, and small cannons. Control the roof to reduce vibration damage. Because of the adoption of the encryption bracket, the reduction of the top distance, the rafting near the fault, the stratum support layer, and the placement of the small gun, the effect of effectively controlling the local roof at the fault zone is achieved.

2.8 Most of the broken roof rock layers have lost their support ability. At this time, the roof rock layer can only be stabilized by the support of the bracket. The force acting on the bracket is the “fixed load” weight of the established broken rock mass. Fully mechanized mining and fully mechanized caving face must be done to prevent the roof from falling. In the event of a roof leakage phenomenon, a void is formed above the top beam of the bracket, so that the bracket cannot be effectively supported on the top plate of the bracket and is in an unsupported state. Under the action of the mine pressure, the fracture will continue to break and even leak. . In order to prevent local leakage, first consider the selection of the bracket to prevent the joint between the bracket front beam and the adjacent bracket of the telescopic front beam section from being too large. The ZFSB4400/16/28 bracket originally used in our mine, the front beam and the front of the telescopic The joint between the adjacent brackets of the beam section sometimes reaches more than 0.2 meters. The broken coal and broken smash of the broken roof are easily leaked from the seam and the top of the bracket is empty, so that accidents such as accidents occur frequently. Later ZFSB3800/16/28 type brackets have been improved, which greatly reduced the occurrence of leakage accidents. In the case of defects in the bracket itself, in order to reduce the occurrence of coal leakage and leakage of the broken roof, the mine adopted a roof. The method of paving the diamond mesh before the harbinger is strengthened to prevent the expected effect; the netting is stopped when the roof is fundamentally improved, thereby reducing the cost per ton of coal. The YFJ2200/16/24 type top-loading coal hydraulic support used by the Yaoqiao Mine Coal Mining Team has a smaller frame joint, and almost no leakage or leakage occurs.

2.9 The phenomenon of the top leakage of the broken roof occurs not only in the frame of the bracket, but also in the front of the bracket, that is, the position of the beam end. Since the bracket itself cannot support the position of the beam end, the position of the beam end is in an empty top state. For fully mechanized mining and fully mechanized caving face, it is best to minimize the beam end distance. If possible, the beam end distance is zero. In the serious working face of the piece, the bracket itself cannot support the coal wall anyway and leave no support space. In this case, temporary support is used to control the top plate. The measures we have taken are to use a semi-circular wood with a diameter of more than 300mm, a thickness of more than 150mm and a length of 2.4-3m for temporary support of one beam and three columns close to the coal gang. When the shearer cuts to this position, the monomer is changed. It is more practical during the closing period, and the relative influence time is longer in the normal normal mining process. For the latter case, we can use the rebar of 28mm diameter or 32mm diameter to hit the coal body at 0.1m below the front beam of the bracket. Set to move ahead. According to the degree of fracture of the top plate, the spacing of the rebar is determined. The spacing of the rebar is generally controlled between 300-500mm. The rebar must be set to be consistent with the pitch angle of the working surface to prevent the rebar from entering the bracket and affecting the production. . The rebar can be used to support the top plate. In order to prevent the old pond side rebar from being pressed by the top plate during the over-bracket process, a semi-circular or large plate can be placed on the support to provide a support point for the rebar and the rebar is set. The direction of the fault is as vertical as possible.

2.10 When over-crushing the top plate, the bracket worker must adhere to the pressure-removing top-loading frame to minimize the amount of roof-sinking. In order to increase the speed of the bracket with pressure-removing frame, the supporting unit can be selected according to the height of the working surface bracket. The bottom of the unit is placed in the base socket of the adjacent bracket, and the upper part is placed above the front beam of the bracket to assist in the movement. At the same time, the coal machine driver should avoid the position of the infeed near the fault when crossing the fault, and at the same time cutting the coal. As far as possible, the friction support of the significant top plate and the fault plane is promoted from the upper plate of the fault to the lower disk. Therefore, it is very important to strengthen the on-site management of the work surface and standardize the operational behavior of employees.

Through the analysis of the characteristics of the roof and the mechanism of the broken roof, we have taken a series of measures to control the local roof accident of the mine roof. Therefore, in order to effectively control local roofing, it is necessary to formulate specific measures to control local roofing, strengthen the management and observation of the broken roof, and conduct statistics on local roofing accidents, sum up the rules, so as to take countermeasures to prevent problems before they occur. It even prevents the occurrence of the top of the broken roof.

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