First, the concept of coal and gas outburst
Coal and gas outburst refers to the dynamic phenomenon caused by coal and gas suddenly thrown from the coal (rock) wall into the tunnel space in a short period of time. In the process of coal and gas outburst, the coal body thrown is several tens of tons to several thousand tons, and a large amount of gas is poured out to fill the entire roadway space. According to the current research results, the forces causing coal and gas outburst have ground stress and gas pressure.
Second, the danger of coal and gas outburst
1. The generated high-pressure gas flow can destroy the roadway, causing the wind flow to reverse and destroy the mine ventilation system.
2. A large amount of coal rock is sprayed to cause the construction workers to be buried.
3. The wells are full of gas, causing people to suffocate, causing gas to burn or explode.
Third, the form and basic characteristics of coal and gas outburst
1. Stand out. The combination of ground stress and gas pressure does not determine the effect of gravity.
(1) The protruding outward throwing distance is far away and has a sorting phenomenon;
(2) The angle of coal thrown is less than the natural angle of repose;
(3) The thrown coal has a high degree of fragmentation and contains a large amount of coal and fine coal powder;
(4) There are obvious dynamic effects, destroying the bracket, pushing down the mine car, destroying and throwing out the facilities installed in the roadway;
(5) There is a large amount of gas effluent, and the gas effluent amount greatly exceeds the gas content of the protruding coal, sometimes reversing the wind flow;
(6) The protruding holes are in the shape of pears, tongues, inverted bottles and other special shapes with small cavities.
2, pressed out. The main factor is the in-situ stress caused by mining, and the gas pressure and the self-weight of coal are secondary factors.
(1) There are two forms of extrusion, that is, the overall displacement of coal and the throwing of coal at a certain distance, but the displacement and the throwing distance are small;
(2) After extrusion, in the crack between the coal seam and the top plate, fine coal powder is often left, and a large amount of cracks are present on the coal body with overall displacement;
(3) The extruded coal is in the form of a block with no sorting phenomenon;
(4) The amount of gas emission from the roadway increases;
(5) Press out a wedge-shaped hole that may be free of holes or large cavities.
3. Pour out. The main factors are ground stress and gravity.
(1) The poured coal is piled up in the natural rest angle, and there is no sorting phenomenon;
(2) hole was decanted small hole large cavity, or bore axis inclined lead seam along the vertical direction;
(3) No obvious dynamic effects;
(4) Deposition often occurs in a steeply inclined coal seam with soft media;
(5) The amount of gas emission from the roadway has increased significantly.
4. Highlight the basic characteristics of dangerous coal seams
There are obvious differences in the medium, structure, occurrence conditions and characteristics of the prominent coal seams and non-protrusive coal seams. These differences are the basis for the evaluation of the outstanding risk of coal seams. In general, the prominent dangerous coal seam has the following characteristics:
1. It has a high degree of deterioration.
2. It has high gas pressure and gas content. (0.74MPa, 8m3/t)
3. The gas permeability is low, and the top and bottom plates are generally closed.
4. The structure damage type is high and the strength is low. (III, IV, V, f<0.5)
5. The initial velocity of gas emission is large. 10m2MPa·d
6. The prominent dangerous coal seam has obvious pore structure characteristics that are different from non-protruding coal seams. There are many large holes and few small holes.
★ In one of the following situations in the outburst coal seam, it is considered to be a dangerous working surface:
1. Structural failure zones in prominent coal seams, including faults, folds, igneous rock intrusions, etc.;
2. The area where the coal seam occurrence conditions change drastically;
3. The area where the mining stress is superimposed;
4. In the process of predicting the working surface, there are power phenomena such as nozzle holes and top drills;
5. The working surface has obvious obvious signs.
5. General rules of coal and gas outburst
(1) As the degree of deepening increases, the risk of protrusion increases.
(2) The protrusion strength increases with the thickness of the coal seam, especially the thickness of the soft delamination.
(3) The greater the gas content and gas pressure, the more serious the hazard. The prominent gas is mainly gas, and in a few cases it highlights carbon dioxide.
(4) The more serious the damage of coal, the smaller the strength of coal and the greater the danger of protrusion.
(5) The protrusion from the top to the bottom is the majority, and the protrusion from the bottom to the top is very small. The outstanding hazard increases as the dip angle of the coal seam increases.
(6) Prominence is closely related to geological structure.
(7) In areas where stress is concentrated in mining, the risk is highlighted.
(8) Compared with other types of roadways, Shimen uncovers the most dangerous hazard and has the highest outstanding strength. The outburst is generally more in the coal roadway excavation, followed by the mining work surface.
(9) Prominence mainly occurs when the working surface is fired, and other vibrating operations or roofing can also induce protrusion.
(10) The poorer the gas permeability of the top and bottom of the coal seam, the more favorable it is for the storage of coal seam gas, the greater the risk of its outstanding.
(11) There are generally signs before the protrusion: the pressure of the coal body and the support increases, the movement of the coal wall is intensified, the coal bulges outward, the shovel falls, the coal falls off, the coal is shot out, there is a cracking sound, the coal cannon sound, like a sports car The same squeaking thunder, coal dust becomes larger, gas is suddenly big and small, the temperature is lowered or raised, top drill or clamp drill, coal hardness changes, coal quality is dry, gloss is dark, and layering is disordered. It is very important to grasp the signs and take timely measures to ensure the safety of personnel.
Sixth, the characteristics of all kinds of roadways
The types of roadways are different, and the prominent conditions are different. This causes certain changes in the effects of prominent factors to form prominent features.
(1) Shimen protruding
There are three types of stone gates: the protrusion when the coal seam is uncovered, the extension of the extension, and the protrusion when the coal gate passes. Among them, the outstanding proportion of the coal seam when uncovering the coal seam is the most important because it is most advantageous for the occurrence of outstanding conditions.
1. Prominence when blasting uncovers coal seams
Before Shimen uncovers the coal seam, if the gas in the coal seam is not discharged, the original high gas pressure is preserved. When the shot is uncovered, the high gas pressure and certain ground stress may cause the surface layer of the exposed coal (rock) wall to suddenly break, and the broken coal (rock) is expanded by the high pressure gas. The belt is thrown into the roadway, and this chain breakage throwing process makes the protrusion expand deep into the coal body. Judging from the prominent types, most of the protrusions in the blasting of the coal seams are of the gas outburst type. In addition to the basic features of gas outburst, they also have the following characteristics:
(1) The straight road near the protruding point is almost completely covered by the protruding coal, and the curved roadway or the mountain is also piled up;
(2) Sometimes only a certain layer or a certain layer of coal seams protrudes, and the protruding holes expand along these layers;
(3) The position and depth of the protruding holes are mainly controlled by the gas pressure and the distribution of coal structure. In many large protrusions, the protruding holes often go deep beyond the concentrated stress zone of the roadway, and the depth is more than 10 meters.
The most important thing to prevent the opening of Shimen is to take measures to pre-discharge coal gas in a certain range around the roadway. For the stone gates that open the coal seam from the bottom plate, the gas of the coal body should be pre-discharged. For the stone gates that open the coal seam from the roof, the gas of the coal surrounding the Shimen, including the coal at the bottom of the stone gate, is pre-arranged.
2, postponed
This kind of protrusion is a sudden delay after the vibration gun is released, which poses a great threat to safety production. The reasons for the prolonged extension have not been fully studied. It takes a certain amount of time to start the projecting, usually within a few seconds to tens of seconds, but the time required for the extension is longer, some hours to tens of hours. This shows that the prominent factors of launching and developing are closely related. If the shot is not prominent, it means that the internal conditions are not mature at this time, and it takes a certain time to complete the outstanding conditions. During this period, certain changes occur in the coal seam, resulting in the accumulation process of energy. If there is no timely support or unqualified support after blasting, the stability of the coal wall will gradually decrease with time, the stress of the hard coal body will gradually increase, and when the coal body suddenly breaks, the thrust of the gas is also suddenly due to the crack. The increase is multiplied, leading to a prominent occurrence.
The basic measures to prevent prolonged extension are to identify the geology, pre-discharge the gas, properly blast, and strengthen the support.
3. Prominence when crossing the coal gate
When the coal seam is uncovered, due to the high ground stress, the permeability of the coal is very low. Therefore, high pressure gas is still accumulated near the coal wall around the coal gate, and the coal body near the coal wall also has a high stress state and is in an unstable equilibrium state. The overloaded coal body, even if it is a small vibration force, will make it lose its balance and induce protrusion. A considerable part of this type of protrusion is initiated by the ground stress. At this time, if for some reason, such as shooting, when the strong ground pressure is induced, the coal body is broken, and the high-pressure gas can be thrown out of the coal rock by several tens of meters.
To prevent such protrusions, there are technically measures to relieve pressure and pre-discharge gas. Pressure relief measures are taken in high-stress areas, such as pressure relief drilling, coal seam water injection, hydraulic punching, etc., or pre-discharge gas measures, or pressure relief and pre-discharge gas mixing. Both types of measures should be accompanied by qualified support measures.
Among the above-mentioned three types of stone gates, the number of protrusions is the highest when the coal seam is uncovered. In addition to the prolonged extension, the other major categories are mostly induced by shooting. Because Shimen has the strongest protruding strength, when uncovering coal seams or passing through coal gates, it is necessary to strictly implement long-range shooting measures to evacuate personnel to an absolutely safe location. It is best to evacuate all personnel to the ground, shut down underground, and use downhole. At the time of handover, the gun was fired on the ground.
(2) Prominence of coal roadway
There are three types of protrusions in coal roadway excavation. Compared with Shihmen's protrusion, the proportion of gas outburst type in coal lanes decreases, while the proportion of extrusion and dumping types increases, and the outstanding average strength decreases. In some special occasions, such as the upper and lower coal pillars with high stress concentration factors, especially when the coal pillars are located in geological structural belts with geological structural forces, the elastic energy accumulated in the coal seams is often high and the geostress is large. The permeability is very low, and it can close the high-pressure gas. When the protrusion is extended to the deep part of the coal body without discharging the gas, the high-strength protrusion will also occur, which is very noteworthy. Therefore, in the tunnels where the ground stress is abnormal, the risk of protrusion is greatly increased, and effective preventive measures must be taken.
(3) Standing up the mountain
There are three types of protrusions in the mountain excavation, but the type of dumping is significantly increased, especially in steeply inclined coal seams. The outstanding strength of the uphill mountain is similar to that of the flat coal seam in the gently inclined coal seam. The strength of the inclined and steeply inclined coal seam is smaller than that of the flat roadway, which is because the gravity of the coal is easy to appear. In the outburst coal seams, the danger is higher.
(four) down the mountain
There are two types of highlights in the excavation of the mountain, that is, protruding from the extrusion. At this time, gravity is a prominent resistance, so it is generally not seen. The strength is similar to that of a flat road, generally without holes.
(5) Highlighting the working face
The outstanding statistics of many mining areas indicate that there are fewer prominent phenomena in the mining face. A complex area of ​​geological formation that generally occurs.
(1) Located near the oblique axis portion.
(2) Located at the intersection of the oblique axis and another fracture fold.
(3) Located in the small fault group and the top or bottom plate convex depression group.
(4) Areas of sudden change in coal thickness and inclination.
7. Analysis of the causes of coal and gas outburst
Before and after the occurrence of coal and gas outburst, there are various anomalous manifestations of geological tectonic stress and mechanical properties of geostress, gas and coal seams. In summary, there are three main factors that occur prominently: geostress, gas and coal structure. Each of these highlights has these three factors working at the same time. The first two factors are the driving forces that lead to the emergence and development. The latter factor is the force that hinders the emergence. If the first two factors take the dominant position, that is, the stress caused by the ground stress and the gas pressure applied to the coal body is greater than the breaking strength of the coal, a prominent phenomenon may occur; when the latter factor takes the dominant position, No prominent phenomena occur. If in the region where the first two factors are dominant, measures to reduce the in-situ stress and to extract gas or increase the strength of the coal are artificially caused to artificially cause the latter factor to take the dominant position, then the outstanding danger can be eliminated, thereby achieving Safe Production.
(1) Highlight the specific cause of the occurrence
Prominent mines should generally have sound organizational structures, better management systems, necessary technical equipment and anti-burst measures. Generally speaking, no prominent accidents should occur. However, due to various factors, outstanding accidents still occur from time to time. The main reasons are:
1. The idea of ​​anti-protrusion work is paralyzed, the emphasis is not enough, and no practical anti-burst measures are taken according to the regulations.
2. Inadequate implementation of comprehensive measures against outbreaks.
3. There is a lack of seriousness in implementing anti-burst measures.
4. Do not conscientiously formulate effective anti-burst measures and establish measures effectiveness inspection system in accordance with the provisions of the “Safety Regulations for Coal Mines†and the “Protection Regulationsâ€.
5. Error prevention prediction or effect inspection error.
6. Neglected in safety protection measures.
7. The lack of advanced and reliable advanced exploration structures and instruments and equipment for highlighting dangerous predictions have affected the forecasting and forecasting effects to some extent. Some also highlight the original anti-burst measures, technical equipment and operating processes after the changes in the local quality conditions of the mines. I have not adapted, but I have not found a new solution.
8. The operator lacks common sense of coal and gas. For example, lack of awareness and understanding of the prominent omen, but also fortunately, no precautions.
Eight, the development of anti-burst measures
As far as the defense prevention measures are concerned, they can be summarized into three stages of development. The first stage is the stage of safety protection measures, the main measure is the vibrating shot. Under the condition that the personnel are away from the working surface, the vibration cannon is induced to protrude to ensure personal safety. The second stage is the stage of universal adoption of prevention of outstanding technical measures, that is, the uncovering of coal seams in Shimen and the mining face of outburst coal seams, such as mining protection layer, advanced drilling, loose blasting, etc. Assist in the use of safety precautions. The third stage is the two “four in one†comprehensive measures to further improve the effectiveness of the anti-burst measures.
The "Anti-Sudden Regulations" require that two "four-in-one" comprehensive measures must be taken when mining outburst coal seams, including:
Regional comprehensive anti-burst measures include the following:
1. Regional outstanding risk prediction;
2. Regional anti-burst measures;
3. Inspection of the effectiveness of regional measures;
4. Regional verification.
Local comprehensive anti-burst measures include the following:
1. The work surface highlights the risk prediction;
2. Anti-burst measures on the working surface;
3. Inspection of the effect of the work surface measures;
4. Safety protection measures.
Highlighting risk prediction is the first step in comprehensive prevention measures. The purpose of the forecast is to identify areas and locations that highlight hazards in order to make the implementation of the outbreak prevention measures more targeted.
The prevention and control measures are the second link of the comprehensive prevention measures. It is the first line of defense to prevent the occurrence of prominent accidents, that is, to prevent the occurrence of protrusions. Outburst prevention measures are only applied in areas and sections where significant hazards are predicted.
The effect test of the anti-burst measures is the third link of the comprehensive prevention measures. The purpose is to test whether the forecast indicators fall below the prominent hazard value after the measures are implemented to ensure the anti-burst effect of the anti-burst measures.
The fourth step of the comprehensive measures for the prevention of security measures is to prevent the occurrence of a prominent line of defense. The purpose of safety protection measures is to highlight accidents or prevent accidents when accidents occur.
Nine, the conclusion
Prevention of coal and gas outburst is a complex system engineering, and there is a long way to go. In the work of preventing coal and gas outburst, people have been making unremitting efforts in two aspects. First, study the mechanism of coal and gas outburst, and master the law of occurrence and development so that theory can be used to guide practice. However, since the prominence is a particularly complicated process, people have not fully understood the outstanding essence in theory. So far, there is no outstanding prediction method or prevention method directly derived from the prominent theory for the coal mine site. Second, study the prominent prediction methods used in coal mine sites and highlight prevention methods. This kind of research is based on the experience of the field, summarizing the relevant data, forming some methods for on-site application, and then continuously improving in practice. Due to the many factors that have prominent influences, the geological conditions of each mining area are different. There are different prediction thresholds that vary with the mine, and the effects of the anti-burst measures are quite different. However, as long as we firmly establish a prominent accident is an anti-controllable idea, we must firmly believe in victory, and take scientific and reasonable comprehensive anti-burst measures, we will be able to overcome this natural disaster.
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