Impact ground pressure mechanism and prevention in coal mining in China

Fund Project: National Key Basic Research and Development Program (973) Funded Project (2010CB226800); National Natural Science Foundation of China (51174213); China University of Mining and Technology National Key for Coal Resources and Safe Mining. Material instability type (b) Slip-shift type (c) Three types of structure-stabilized impact ground pressure Schematic shift-type impact ground pressure.
The slip-type displacement ground pressure, as shown in (b), refers to the coal seam slip-off impact extrusion caused by the difference between the top and bottom plates and the coal seam stiffness under the influence of mining, such as the coal seam translation of the Lippmann study. Model 5; or a kinetic phenomenon of sudden and severe damage induced by slippage of faults, structures, or structural surfaces near the well.
Structural instability type impact ground pressure.
The rock mass around the roadway or working face, due to the mining stress or the sudden breaking of the large-area suspended roof or the sudden earthquake damage caused by the mining earthquake, often the impact of the large area of ​​the coal pillar or roadway surrounding rock is prominent and the whole occurs. The structure of the shaft is unstable, as shown in (c). Such as the mining of the island working face, the recovery of coal pillars, coal mining under the hard roof. For example, in 2008-06-05 Qianqiu Coal Mine, a ground pressure accident occurred, and the huge energy released by the surrounding rock in the stope caused the 105m long roadway project to have outstanding impact damage.
In the practice of coal mining, the damage caused by the impact ground pressure of the second and third types is usually more severe than that of the first type. Such impact ground pressure is large, kinetic energy, and vibration is large, which often causes great damage and Serious consequences.
2 The mechanism of impact ground pressure and the key scientific problems in the research of prevention and control The production practice shows that there is no obvious macroscopic precursor of the dynamic disaster phenomenon of coal mine impact, which has sudden, transient vibration and great destructive characteristics. It is difficult to determine when, where, and how strong it is. In terms of mechanics, coal mine rockburst is a nonlinear dynamic process of coal-rock system under specific geological conditions due to the steady state accumulation of energy during the deformation and failure of mining activities, and the non-steady state release. The comprehensive reflection of environment, internal structure, structure and its physical and mechanical properties is very complicated, involving interdisciplinary subjects such as geology, mining, geophysics, rock mechanics and nonlinear dynamics. At the same time, the problem has obvious characteristics of space-time evolution.
Compared with underground projects in other underground industries such as underground powerhouses, hydropower chambers, and subway tunnels, coal mining has very distinctive features: 1 The mining space is large. The deep-wall mining methods in China's deep coal mines have formed hundreds of thousands or even millions of cubic meters of mining space. The large mining area and the wide range of mining are unmatched by any other underground engineering. 2 Mining disturbance is strong. The longwall mining method in the large space rapid mining has caused strong mining disturbance to the surrounding rock, causing the overburden strata to fall and the large-scale deformation and settlement of the surface, especially for the 10 million-ton mine that is concentrated on one side of the deep one mine. The large-scale strong disturbances caused by shallow mining and other underground engineering are unmatched. 3 media properties and stress states are complex. In addition to the complexity of geological conditions in deep coal fields, large-scale mining has repeatedly disturbed the coal and rock mass around the mining space, causing it to undergo deformation and destruction processes many times, resulting in the media properties of the coal and rock mass having both intermittent structural features. It also has the property of breaking medium; under the joint action of high ground stress and strong unloading, the space-time relationship of mining induced stress redistribution is complex, the energy dissipation of coal and rock mass caused by high stress release, transfer and transmission and the power of energy release process The characteristics of the school are obvious, and it is easy to induce the impact of ground pressure and power disaster.
Through years of research, Chinese scholars have proposed four key scientific problems that need to be solved in the field of rockburst and prevention technology in coal mining: the mechanism of action and the quantitative analysis method of geological conditions on impact ground pressure.
In the long-term geological evolution process, the deep coal mass contains huge deformation energy. The energy storage degree and the original rock stress distribution depend on the hardness, compactness and mineral composition of the coal rock mass, and also depend on the geological structure and fault. The extent of the fold. At the same time, the instability of the hard roof (especially the thick sandstone roof) during the deep coal seam mining is also the cause of the transient impact dynamic disaster caused by the pillar and stopway working face.
Therefore, the impact of ground pressure hazard is closely related to coal rock composition, fault, fold, primitive stress field and tectonic stress anomaly. How to scientifically and quantitatively describe the mechanism of geological occurrence conditions and its correlation with coal mine rockburst disaster is a common science problem. By studying this scientific problem, it reveals the impact mechanism of coal rock mass impact tendency, geological structure and original rock stress conditions on coal mine deep well dynamic disaster disaster.
Deformation and failure law and engineering dynamic response characteristics of deep intermittent coal and rock mass.
The deep coal rock mass is usually a layered structure containing joint fissures.
The concentrated mining of deep coal is strongly disturbed, which causes the coal and rock mass around the stope and the roadway to inevitably deform and destroy to form an intermittent structure. During the multiple mining disturbances and long-term rheological processes, the discontinuous structural coal and rock mass will have new cycles of rupture and continuous decay, resulting in large deformation, strong rheology and ultra-low friction effects. Under the conditions, it will cause an impact of ground pressure and power disaster. In the deep coal mining project, the destruction of the surrounding rock of the roadway does not mean the failure of the roadway. The sudden dynamic damage of the surrounding rock is due to the structural characteristics of the discontinuous coal rock mass, the external load, the rock pressure relief and the energy release. The result of the action. Therefore, by exploring the scientific problems of deformation and failure regularity and engineering dynamic response characteristics of deep discontinuous coal and rock mass, the structural characteristics of discontinuous coal and the deformation and failure characteristics after fracture are studied, and the deformation of surrounding rock is allowed but the deformation development is restricted. Stable conditions, so as to understand the mechanical response of the surrounding rock after the rupture of the roadway (post-peak), the instability characteristics of the surrounding rock and its evolution law and dynamic instability control measures.
The mining stress distribution, the space-time evolution law of the energy field and the multi-factor coupling disaster mechanism.
Before the mining, the coal and rock mass is in the deep three-dimensional stress equilibrium state, and the mining activity breaks the original stress balance, which leads to the redistribution of the macroscopic stress field and the energy field in the three-dimensional space of the stope. The dynamic evolution of the stress field and the energy field And development will inevitably create conditions for the birth, occurrence and development of dynamic disasters. Therefore, by studying the temporal and spatial evolution of the mining stress distribution and energy field and the multi-factor coupling disaster mechanism, it is possible to reveal the energy accumulation and release mechanism of the deep fractured coal and rock mass during the mining process, the space-time evolution of the energy field and the dynamic catastrophic Based on the energy triggering conditions, a model, criterion and energy analysis system for dynamic instability of deep coal and rock mass based on energy mutation are proposed.
The theory and method of multi-parameter monitoring, early warning and prevention of impact ground pressure.
During the development of the impact and pressure dynamic disaster, the stress state in the coal and rock mass will change and be accompanied by the release of energy. Among them, microseismic, acoustic emission and electromagnetic radiation are the physical effects of this release process. Study the precursory information law of stress, microseismic, acoustic emission and electromagnetic radiation in the process of deformation and failure of coal and rock mass, and monitor and analyze the stress changes and microseismic, acoustic emission and electromagnetic radiation activities of coal and rock mass near the roadway and stope. The multi-parameter dynamic change trend of precursor information can establish the impact ground pressure monitoring and early warning system for early warning and effective prevention. At the same time, starting from the conditions of dynamic disasters such as impact and pressure, the mechanism of controlling the distribution of mining roadway layout, mining sequence and protective layer mining is discussed. The new mine is studied in the mining design stage or the produced mine is used in the unmined area. Reasonable mining design and protective layer mining to prevent the occurrence of dynamic disasters such as impact and ground pressure, and put forward the theory and method of optimizing mining design for deep mining in coal mines.
3 Research status and existing problems of impact ground pressure generation mechanism and prevention technology 3.1 Geological structure conditions and interaction mechanism of coal mine impact rock pressure Formation of deep coal mine impact ground pressure and deep geology characteristics, tectonic formation and evolution process and regional stress environment There are close relationships between factors, and the geological evolution experienced by deep coal seams controls the occurrence, distribution and thickness of coal seams, affecting the occurrence of geological structures, the distribution of tectonic stress fields or residual stress fields. The dynamic movement of geology has produced a variety of geological structures, and the characteristics of these structures directly determine the occurrence conditions of mine geological disasters, and are also the main factors that induce the impact pressure of coal mines.
Studies have shown that the impact tendency of coal rock, the occurrence of faults and folds, and the occurrence conditions of overlying strata are the main geological conditions for inducing impact ground pressure.
The coal seam impact tendency index was first proposed by Polish scholars. China currently uses four indexes of elastic energy index, impact energy index, dynamic failure time and uniaxial compressive strength as the impact tendency index of coal seam. Through the statistics of mines with impact pressure in China in the past 10 years, the strong impact tendency accounted for 29%, the medium impact tendency accounted for 8%, the weak impact tendency accounted for 38%, and the non-impact tendency identification accounted for 25%. It shows that most of the coal seams that have impacted the ground pressure have a tendency to impact. However, impact pressures have also occurred in mines that have no impact tendency. For example, Xuzhou Quantai Mine, Pingdingshan 10 Mine and Beijing Da'anshan Mine are weak and non-impact coal seams. considering. It should be pointed out that the monitoring principles of different monitoring systems are different, the monitoring objects, effective accuracy, and monitoring range are also different. How to get the correct warning results from these precursor information still has a long way to go. For example, Yima Qianqiu Coal Mine has installed ARAMIS, ESG microseismic monitoring system and monitoring equipment such as KBD-5 and KBD -7 electromagnetic radiation meter, but it has not been able to make predictions for the “11.3” impact ground pressure accident that occurred in 2011.
The prevention and control technology of impact ground pressure can be roughly divided into three types: First, the mining optimization design method is adopted to avoid the occurrence of impact ground pressure, including optimization of development layout, liberation layer mining, coal pillarless mining, pre-excavation pressure relief lane, and width. Roadway excavation, wide roadway column method, etc.; second, to solve the problem of areas with impact danger, avoid high stress concentration and improve the medium properties of coal and rock mass to weaken the ability to accumulate elastic energy, including roof deep hole blasting, coal seam unloading Blasting, coal seam high pressure water injection, large hole pressure relief method, directional hydraulic fracturing method, high pressure water jet grooving, bottom blasting method, pre-drilling pressure relief chamber, coal seam high pressure hydraulic fracturing, floor grooving method, etc.; Using more effective support methods, by increasing the strength of the support or improving the support method to improve the ability of the support body to resist impact, this is a passive protection method, such as the impact vibration roadway surrounding rock rigid soft energy storage support method, high Prestressed, strong bolt U-shaped steel support method, portal hydraulic support (or hydraulic support), constant resistance large deformation anchor (cable) support method. It should be pointed out that the mining design optimization method is a kind of method to eliminate the high concentration of stress from the source and reduce the risk of impact ground pressure. At present, many impact ground pressure mines do not consider the stress superposition and concentration problems in the mining during the mining design stage, resulting in In the post-production and production, there is a situation of silo coal pillar mining and mining under the coal pillar. If the mining design optimization method such as roadway layout optimization and protective layer mining can achieve the purpose of eliminating the stress concentration caused by multiple superposition of stress.
The technical management system for impact rock pressure and the design of anti-shock work flow are also very important. For example, Shandong Energy Group has formulated eight strict regulations on impact ground pressure mine and severely impacted ground pressure coal seam production: impact ground pressure before mining Risk assessment, optimization of mining design scheme, anti-shock pre-treatment before mining, monitoring and early warning during mining, danger zone in the mining process, inspection of the effect of disarming, safety management of impact ground face, impact ground pressure The summary of prevention and treatment experience has established three systems and one process of “anti-shocking”, namely, organizational system (anti-shocking personnel), technical system (technology, equipment investment), management system (related anti-shock management system) and closed-loop work. The process, in the technical system, focuses on the “three strong” anti-shock technology in the danger zone, namely strong pressure relief, strong monitoring and strong protection, and achieved better anti-shock effect.
In order to meet the major demand for monitoring and early warning of deep ground coal mine pressure, the monitoring, early warning theory, technology and means of deep well impact ground pressure need to be improved. At the same time, the mechanism research on the prevention and control method of rockburst at home and abroad lags behind the practice of prevention and control of rockburst. Therefore, the theoretical research on the mechanism and prevention method of dynamic earthquakes such as rockburst is still the long-term goal of research on the impact of ground pressure dynamic disaster. On the basis of equipment early warning monitoring equipment, from the aspects of optimizing mining design, changing the distribution of mining stress field and improving the properties of local coal and rock mass, the theory of impact rock pressure in deep coal mines and the technical methods of impact ground pressure relief are established. The theory and technical system of comprehensive prevention and control of deep rockburst in coal mines in China is an important guarantee for the effective prevention and control of rock and rock impact pressure such as rock burst.
4 Conclusion The essence of coal mine rockburst is the nonlinear dynamic process of coal rock mass system due to the steady state accumulation of energy during the deformation and failure process, and the unsteady state release. The impact pressure is based on the instability form and the instability mechanism. Classification can be divided into three types: material instability type impact, slip misalignment type impact and structural instability type impact.
The research on impact ground pressure in coal mining needs to solve four scientific problems: the mechanism of action and quantitative analysis method of geological occurrence environment on impact ground pressure, deformation and failure law of deep intermittent coal and rock mass and engineering dynamic response characteristics, The temporal and spatial evolution of mining stress distribution and energy field and the multi-factor coupling disaster mechanism, monitoring and early warning and prevention methods of coal mine impact ground pressure, the solution of these problems is helpful to reveal the mechanism of impact ground pressure and propose effective prevention and control methods. To ensure the safe and efficient mining of coal resources.
The research on the impact pressure in deep coal mining in China has obtained a series of research results, but the relationship between the geological structure characteristics of deep coal seams, the spatial structure of coal strata and dynamic disasters, and the spatial evolution law of stope stress in deep mining are still needed. The disaster mechanism, theoretical research on the method of prevention and control of rockburst will be further explored.
Due to space limitations, a large number of charts and formulas have been omitted from the text, and thanks to Wang Tao and Zhu Jie for their contributions to the formation of this article.

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