Is there an earthquake in the mining area?
The traditional earthquake refers to a natural phenomenon in which the earth's crust generates seismic waves during the release of energy due to structural effects. In the case of mining operations, earthquakes may also occur in mines. This kind of induced earthquake caused by mining activities is called “mine shockâ€.
China's first mine earthquake reported in 1933. seen in Fushun coal mine victory, and now with the increase over time as well as the depth of the mine, a sharp increase in the number of mine earthquake. According to the statistics recorded by the Seismic Station, the number of mines in the Fushun mining area is as high as 3000-4500 per year; in some mining areas, due to the mining depth of 1000 meters, the phenomenon of mining earthquakes is very prominent, the scope of impact is large, and the surrounding area is strongly felt. In the China Seismological Network, you can see the distribution map of the mines that have occurred in each mining area.
Causes of mine earthquakes
From the literal point of view, mine shock is the vibration phenomenon in the mining process, and when it comes to mine earthquake, we must first introduce two noun concepts: impact ground pressure, rock burst. Because the mine shock belongs to one of the categories of impact ground pressure, and the impact ground pressure is equivalent to the rock burst within a certain range, first we will explain what is the impact ground pressure.
In coal mines, impact ground pressure refers to the energy accumulated in the mine roadway and the coal and rock mass around the stope, which is released in a sudden, sharp and violent form. The generated power throws the coal rock into the roadway and a strong sound occurs at the same time. vibration coal and rock mass destruction, stand and equipment damage, casualties, some of roadway collapse destruction; and in metal and nonmetal mines, rock burst phenomena collectively referred to as rock burst.
Mine shock belongs to one of the categories of impact ground pressure. Under the influence of regional stress field and mining activity, the mining area and surrounding stress are in an abnormal state of instability and instability. After accumulating a certain amount of energy in local areas, impact or gravity The formation vibration is released by the release of the action mode. In the case of strong earthquakes, the vibration of the rock mass can be felt on the ground, and even the buildings on the ground are destroyed. In simple terms, the cause of the mine earthquake is that the mining area artificially changed the originally stable crustal structure, resulting in uneven earthquakes in the earth's crust.
Definition of mine earthquake, impact compression and rock burst
In fact, impact rock pressure, rock burst and mine shock, although they have certain similarities, or can be replaced with each other to a certain extent, they are in terms of phenomena, the lithology of the medium, or the mechanism of occurrence. There are substantial differences in control methods. For the definition of the relationship between the three, Dr. Du Xueling from Guizhou University of Technology discussed the relationship between mine shock and impact pressure and the relationship between rockburst and rockburst:
1. Definition of mine earthquake and impact ground pressure
(1) Dependency definition
When the impact ground pressure occurs along with the deformation of the roadway and other dynamic phenomena, the formation vibration will occur in this process, so the impact ground pressure must be accompanied by the mine shock, and vice versa.
(2) Definition of roadway damage
After the first mining pressure and periodic pressure of the mining site, the roof of the goaf will break and fall. In this process, the rock stratum and the stratum will be caused by the falling roof, which will cause the earthquake. . However, if there is only stratum vibration and there is no destructive instability in the roadway or working face, then such mine shock is not considered to be impact pressure. Therefore, it cannot be simply thought that mine shock is impact rock pressure or impact ground pressure is mine shock. The main feature of mine shock is the vibration event occurring in mine engineering, and the main feature of rockburst is the destructive and disastrous nature of mining space. .
(3) Scope of use
The mining earthquake occurrence environment includes a variety of well mining environments such as coal mines, gypsum mines, and metal mines, and the impact ground pressure is generally used in the underground mining environment of coal mines. The scope of application of the two is also different.
2. Definition of rockburst and impact ground pressure
(1) Physical and mechanical definition
Rockburst and impact ground pressure can be considered equivalent within a certain range. From the perspective of stress, it is believed that both of them have macroscopic damage, and there must be a process in which the stress exceeds the strength limit of the coal and rock mass; from the energy point of view, it is believed that both occur with the dynamic phenomenon, the ejection and movement of the coal and rock mass Wait for the supply of excess energy
(2) Scope of engineering application
Rockburst is more suitable for rock bursting under hard rock conditions such as metal mines, deep tunnels, hydropower projects, etc., and impact ground pressure is more suitable for the severe impact dynamic disasters in underground coal mining, which is the result of the two projects. The environment determines.
The reason is that in the underground mining process of metal mines, the surrounding rock media are generally in the rock environment of engineering hard rock, and it is more appropriate to use rockburst to directly describe the bursting phenomenon of common rocks. As an engineering soft rock, in addition to the impact ground pressure in the rock roadway, the impact ground pressure of the general coal mine is affected by the mining factors, and the occurrence time of the impact instability has more obvious hysteresis, and the impact ground pressure The scope is large and the damage is strong. The “shock†and “ground pressure†respectively describe the dynamic process and stress environment of the disaster, which reflects the special characteristics of the coal mine impact instability. Therefore, the impact pressure is more used in underground coal mining. Suitable. To a certain extent, it can be considered that the impact ground pressure is a violent rockburst in the underground coal mining process, but in the narrow sense, the rockburst and the impact ground pressure are not the same, so the two should be different.
(3) Defining the degree of engineering damage
It is generally believed that the damage caused by the impact of ground pressure is more serious than the rock burst. When rockburst and rockburst are applied to different rock media environments respectively, the degree of engineering damage is not the same. For example, the damage range of a tunnel rock burst may be only a few meters, and the impact ground pressure is often accompanied by severe deformation of the roadway's gangs and bottom drums. The damage ranges from a few meters to several hundred meters, and the mine is severely impacted. There have been instances of extensive damage.
Conclusion
In order to reduce the damage caused by the mining earthquake, the current mining area mainly uses the theoretical analysis method and the field measurement method to monitor the mine earthquake. The former is mainly used in the engineering geological survey or development design stage, through the drilling of ore samples at the site, rock mechanics tests, using one or a set of indicators to analyze the possibility of mine shocks; the latter is to use the necessary instruments to the underground The site or rock mass of the project is directly monitored or tested to determine whether there is a possibility of occurrence of a mine shock. The more advanced methods are the acoustic emission method and the microseismic method.
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