Prevention and control of roof accidents in general mining face
1 Analysis and prevention of the cause of the roof accident when the first roof is placed for the first time
1.1 Initial ceiling features
Before the coal seam is mined, it is balanced with the rock stratum in all directions. After excavating the open cut, the rock layer is damaged by the force balance, the surrounding rock moves and deforms, and a new stress balance is sought. The square on the top plate becomes temporary. Balanced rock loosening ring, when the working face bracket mainly supports the rock weight in the loose ring. The working face begins to pick up, advances forward, the loosening ring gradually expands, and the force on the bracket increases rapidly. If no measures are taken, the rock layer will crush the bracket, causing a roof accident. Therefore, generally after the 6- to 20 m advancement of the open-eye, the support of the goaf is withdrawn in time, and it falls directly against the column, which is the first time. If the stone is not itself of roof collapse, To the gob roof drill blasting a "force roof." The characteristics of the initial topping of the direct roof are as follows: First, the working surface control top area is larger, the pillars are more, and the pressure is also greater; secondly, when the first time is topped, the range of the primary return column is larger, and the roof falling range is also larger. Large; the third is that the manual operation is large and the time is long.
1.2 Causes of roof fall accidents during initial ceilinging
(1) The topping distance selection is unreasonable. When the selection is too large, the top plate pressure before the topping is greater than the supporting resistance, and the roof accident of the pressing working face is prone to occur;
(2) The initial ceiling area is too large, the impact force is large, and it is easy to push down the pillar and cause the roof to fall;
(3) After the initial ceilinging, the direct roof does not completely fall, and coal mining is continued, so that the area of ​​the controlled roof is getting larger and larger, and it is easy to cause a roof accident;
(4) The method of returning to the column is unreasonable, causing the pressure of the roof to concentrate on the local pillars, causing local roof fracture, which is prone to local roof failure;
(5) The pillars are not supported as required, and the initial supporting force is insufficient, causing the roof to sink too much or the supporting resistance is small. After returning to the column, the working face pillars cannot support the roof and the roofing accident occurs;
(6) The return column is generally operated directly by the worker, so the probability of a wounding accident is large.
1.3 Accident case
Case 1: South Tong a mine coal seam thickness of No. 6 0.2 m ~ 1.8 m, the immediate roof containing pyrite calcareous shale, a thickness of 1.9 m ~ 4.86 m, the hard roof of limestone, the thickness of 2.4 m. Seam angle 30 ° ~ 45 °, the use of metal struts friction, which directly faces the direction of the top wall parallel to the coal face fractured, the top plate is divided into chunks. After the mining, the cracks expand, and when the column is returned, the pushing of the large roof to the coal wall or the inclined direction occurs. The cause of the accident was: when the column was returned to the column, the range of the roof was large, and the impact force was formed. The pillar was pushed down, and the support resistance was reduced to cause a large area to fall.
Case 2: 2303 general mining face of a mine, directly to limestone, 2 m ~ 3 m thick, joint development, the old top is interbedded with limestone siltstone . After the accident, after the completion of a knife coal, the working face is returning from the nose to the end of the machine, returning to the middle of the working face and approaching the old alley. It is found that several pillars are drilled to the bottom of the floor 50 cm, and the hinged column is used. Just pulled down, the entire roof (length 18 m, width 7.2 m, thickness 6 m), pushed the pillar down (falling to the coal wall), occurred in the roof, causing 4 deaths. Causes of the accident: First, the quality of the roof support is inferior. On the side of the coal wall, the roof cracks are found to show the existing cracks. No timely and effective measures have been taken, and the tops of the work are still blindly placed, resulting in a large area of ​​the working face. Ineffective, the measures are not targeted, and the hydraulic props of the work surface have individual liquid leakage. The third is that the initial production and initial release responsibility system is not implemented, illegally commanding and operating illegally.
1.4 Preventive measures for roof accidents during initial ceilinging
(1) Determine the reasonable direct top initial step for the specific direct top conditions;
(2) When the first time is put on top, strive to make a topping success, so that the direct top is completely backward, in order to continue mining;
(3) The pillars shall be supported as required, with quality and quantity, so that the pillars can reach the initial support force and support resistance of the design;
(4) Strengthen the support strength and support density of the top line to ensure that the top line is cut at the top line, and at the same time prevent the falling rock from falling into the working surface and pushing down the pillar;
(5) If forced topping is required, the specifications of the blasthole, the amount of charge and the step of firing shall be strictly specified to prevent the collapse of the pillar and the occurrence of a roof accident;
(6) When the first time is placed, the experienced workers are selected to operate, and there are technicians on-site command;
(7) Workers on the working face, especially the team leader, must grasp the signs of the roof of the working face. Once the roof is found, the on-site personnel should quickly take effective emergency measures.
2 Roofing accidents when the old top is first pressed and the cycle is pressed
2.1 Characteristics of initial pressure and cycle pressure
After the initial topping, if the direct top can not fill the goaf, the old top is placed on the coal seams on both sides like a "beam" and supports the weight of the rock above. When the working surface continues to advance, the old top suspension The exposed area is getting bigger and bigger. When it exceeds its own strength, the balance of the beam is destroyed, and the old top is broken and broken. It gives the working face a big sudden pressure, that is, the first time the old top is pressed. The old top is behind the first time, and continues to advance with the working surface. The old top is in the state of a cantilever. When the length of the cantilever reaches a certain length, it breaks off. With the advancement of the working surface, this kind of fall is regular and occurs periodically, and the cycle of the old top is called to press.
When the old top is pressed and the cycle is pressed, the stepping distance is large, the area is large, the strength is high, and the dynamic pressure shock may be accompanied. The mine pressure appears strong, generally has the following characteristics: First, due to the old top Violent activities, the sinking amount and sinking speed of the working face increased sharply; Second, the support force surged, the roof broken, cracks, pieces and even the working surface appeared sinking; the third is the old top broken At the time, the dull thunder was first generated in the depth of the goaf, and then the goaf appeared to fall off, accompanied by a storm when it fell.
2.2 The reason for the initial pressure and cycle of the old top to cause a roof accident
(1) Before the pressure is applied, the pressure on the working surface is small. When the resistance-increasing pillar is used, the pillar is not strong, and it is easy to lose stability when the pressure is applied, resulting in a topping accident.
(2) Before the pressure, due to the insufficient strength of the support, the direct top and the old top are separated from the floor. When the pressure is applied, the old roof forms an impact on the direct roof and causes the accident of the pushing work surface;
(3) The supporting strength of the working face is not enough or the rigid support (such as the wooden pillar), when the old top is pressed, the working face is crushed, causing an accident;
(4) Before the pressure is applied, the concentration of the supporting pressure will cause the top plate near the old top fracture line to be broken. When there is no measures to prevent roofing, a local roofing accident is likely to occur when the pressure is applied;
(5) When the pressure is applied, a large number of pieces of coal wall are caused. When the mining thickness is large, the coal is easy to cause burial and injury. In addition, the area of ​​the empty roof is increased after the film is applied, which is prone to leakage accidents.
2.3 Accident case
Case 1: 2233 cannon face of a mine, # 10 seam thickness 1.8 m, white quartz sandstone roof, thickness 8 m, the base plate is aluminum shale clay, wood prop. When the working surface advances 48 m away from the opening, the old roof is pressed for the first time, and the direct cutting is forced from the coal wall to break the pillar, causing a large roof, killing 4 people and injuring 2 people. Causes of the accident: insufficient support capacity, resulting in the separation of the direct roof and the old roof. When the pressure is applied, the old roof forms a dynamic pressure impact on the direct roof, and a shock-type accident occurs; no specific safety technical measures are formulated according to actual conditions. .
Case 2: A high-grade general mining face of a mine, the direct top is gray-black sandy shale, with a thickness of 0.8 m to 1 m, and the old top is gray-white medium-fine sandstone with a thickness of 5 m to 8 m. After the initial placement, the old The top is obviously not sinking, causing the direct top and the old top to be separated from the floor. When the old top is pressed for the first time, the direct top is cut along the coal wall. As the working face advances along the pseudo-slanting direction, the stratum-breaking rock stratum drives the strut to slide downwards, pushing down the strut (both inclined down and biased toward the goaf), forming a vicious roofing accident. Causes of the accident: First, the resistance of the pillar is small, causing the direct roof and the old roof to be separated from the floor, and the direct roof is cut off when the pressure is applied, so that the direct roof becomes an independent "hexahedron"; the second is that there is no measure to prevent the old roof from sliding downward.
2.4 Preventive measures for roof accidents when the old top is first pressed and the cycle is pressed
(1) Strengthen the basic work of mine roof management. Carefully prepare reasonable operating procedures and strictly implement the operating procedures. When preparing the operating procedures, the basic information obtained from geological prevention and mine pressure observation should be fully utilized, the supporting design of the working face should be well done and the roof management measures should be formulated, and the relevant technical policies and advanced technologies should be implemented to ensure its scientificity and targeting. Sex, and at the same time, according to production conditions and geological changes, timely development of corresponding supplementary measures. Teams must carefully study the operating procedures, and conduct assessments according to the regulations, and operate according to the operating procedures.
(2) The support design should be: First, the support characteristics of the bracket are compatible with the conditions of the top and bottom plates. The friction-increasing friction strut is suitable for the gently inclined coal seam with the roof sinking amount less than 100 mm and the height of 1.3 m or less; the micro-increasing friction metal pillar can be used for the gently inclined or inclined medium-thick coal seam with the roof sinking amount less than 400 mm; Hydraulic struts can be used for gently inclined or inclined coal seams with a roof sinking of less than 600 mm. Columns with different working characteristics cannot be mixed or segmented on the same working surface. Second, determine reasonable support parameters and layout. Support strength and support density are the most important support parameters for the single pillar working face. The support strength is small, which will cause a large area to fall or the roof step to sink, which is easy to cause a roof accident. Excessive support strength also brings disadvantages such as high cost of the bracket and large workload of the support and return column. In some cases, the excessive support strength makes the pillars under the "limited deformation" work plan for the old roof, and the old roof is pressed to give a greater pressure to the direct top, thereby causing the direct roof to break and causing a roof collapse. Therefore, for each working face, reasonable support strength and support density must be determined by calculation according to the specific conditions of the roof. The layout of the basic support of the single-pillar working face shall be determined according to the conditions of the roof: the unstable roof is made of Qiliang Qizhu plus temporary plastering column (or the front beam arrangement); the medium-stabilized roof is arranged by Qiliangqizhu or wrong beam Qizhu; the stable roof can be Use a hooded pole arrangement. Special support plays an important role in enhancing the supporting force and stability of the working face and improving the effect of cutting the top and blocking the raft. Intensive pillars are generally used under the conditions of old top level II and above; when the old roof is first pressed and cycled, it is necessary to use sheds, rafts or increase the density of support.
(3) Further implement the roof management responsibility system, from top to bottom, conscientiously implement and be responsible at all levels. Educate the majority of employees to work standard, live and work hard, and work according to quality standardization standards.
First, to strengthen the quality management of supporting materials, according to the design of each pillar qualified to use and strictly implement the regular maintenance system;
The second is strict engineering quality management, supporting and recycling pillars according to design requirements;
The third is to strictly follow the rules and regulations, and must not violate the rules of command and illegal operations.
(4) Strengthen the quality of support and dynamic monitoring of the roof. Support quality and roof dynamic monitoring is one of the prevention management sciences. By monitoring and forecasting the roof dynamics, support quality and unsafe factors and their changing rules of various parts of coal mining face, timely feasible measures can be made. Effectively control the top plate.
(5) Conduct safety class assessment work. The assessment of the class can be changed into static safety, quality inspection for dynamic inspection, regular inspection for daily inspection, timely reflection of unsafe hidden dangers on the site, and immediate rectification, to achieve the purpose of predictive prevention after the accident. In particular, it is necessary to strengthen the forecasting of the old roof to observe and observe the change of the sinking speed of the roof. When the sinking speed suddenly increases to a certain range, the forecast is issued in time, and necessary measures such as strengthening support are taken to eliminate the cutting along the coal wall. A top or working face pressure type accident occurred.
(6) Strengthen mine geological work. A considerable part of the roof accidents in the mining face is caused by the failure to take timely targeted measures due to geological changes. Geological forecasting is of great significance for reducing roof accidents.
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