Coal and rock dynamic disaster phenomenon is a kind of disaster phenomenon with dynamic effect and disaster consequences under the action of external force. It has the characteristics of wide range and various forms, such as earthquake, volcanic eruption, tunnel instability, landslide, coal and gas outburst, rock burst, roof accident and so on. Which belongs to coal and rock dynamic disasters. The phenomenon of coal and rock dynamic disasters is very harmful, which will cause great casualties and losses to people's lives and property.
Faced with frequent natural disasters, such as hurricanes, droughts, floods, earthquakes, landslides and avalanches, India has established a unique disaster management system. National, state, county and district levels have unified disaster management institutions. India has also formulated a series of pre-disaster preparation and departmental development plans, as well as post-disaster reconstruction plans such as hurricanes and earthquakes [1].
(1) earthquake [2 ~ 8]
As we all know, the earth is always in motion and change. The movement and change of the earth will produce great force, which will deform the underground strata. Deformation is slow at first; But when the force is too great for the rock stratum to bear, it will suddenly break; When the vibration produced by rock fracture reaches the surface, it will cause the vibration of the surface, which is an earthquake. Generally speaking, the longer and wider the deformation zone is, the more energy is released, and the greater the magnitude of the tectonic earthquake is. As shown in figure 1. 1, a picture of Zhang Weixing can clearly see the faults caused by the earthquake, while as shown in figure 1.2, a photo of the San Francisco earthquake scene of 1906 shows that the rupture caused by the earthquake has broken a row of fences that were originally connected together.
Figure 1. 1 satellite image of earthquake fault
Photo 1.2 1906 San Francisco earthquake scene photo.
Earthquake disaster is the first of all disasters, with sudden, unpredictable and high frequency, and produces serious secondary disasters, which will also have a great impact on society. When a strong earthquake occurs, buildings will be destroyed, and at the same time, it will cause surface damage such as landslides, mudslides, ground fissures, ground fissures, sand blasting, water inrush and tsunamis. A series of other disasters caused by the earthquake, including fire, flood, gas and toxic gas leakage, the spread of bacteria and radiation, plague and other disasters caused to life and property.
Annals of Bamboo Records is the earliest written record of earthquakes in the world so far. The book called this earthquake "Taishan Earthquake", which recorded an earthquake phenomenon that occurred in 1830 BC. There are more than 5 million earthquakes in the world every year! However, less than 2% of earthquakes can be felt by people, including more than 100 destructive earthquakes every year, which have caused huge economic losses and casualties to human beings. According to the Internet data of the National Earthquake Information Center (USGS NEIC) of the U.S. Earthquake Survey, in 200 1 year, there were more than 2 1 1,000 earthquake deaths worldwide, among which the earthquake with the largest number of deaths occurred in Gujarat, India on June 26th, 65438, with 20,000 deaths. Strong earthquakes often bring serious harm to social and economic development, human survival safety, social stability and social function with their sudden and huge destructive power. Among the losses caused by various natural disasters, earthquake losses account for 52%, which is a veritable "big head".
China is located between the Pacific Rim seismic belt and the Eurasian seismic belt, squeezed by the Pacific plate, the Indian plate and the Philippine Sea plate, and the seismic fault zones are very developed, with 23 main seismic zones. In the past 20th century, nearly 800 earthquakes of magnitude 6 or above occurred in China, covering all provinces, autonomous regions and municipalities except Guizhou and Zhejiang provinces and the Hong Kong Special Administrative Region. It is one of the countries that suffered the worst earthquake disaster in the world. This is more obvious in the current rapid development of global urbanization, especially in the case of a sharp increase in the number of cities in China. As far as all kinds of natural disasters in China are concerned, among earthquakes, meteorological disasters, marine disasters, geological disasters, crop biological disasters, forestry disasters and other disasters, according to the statistics since the founding of New China for more than 50 years, meteorological disasters account for 57% of the economic losses caused by various disasters, ranking first among disasters, but according to the statistics of population deaths caused by various natural disasters, earthquake disasters account for 54%, making it a group.
The frequent occurrence of earthquakes around the world and the huge losses caused by them put forward a serious research topic for earthquake prediction. However, from a global perspective, earthquake prediction is still in the exploratory stage, mainly based on the empirical prediction of earthquake observation data accumulated for many years, and the occurrence and development law of earthquake preparation mechanism is not completely clear. So today's earthquake prediction has great limitations. Seismologists analyze the earthquake risks in different areas, predict the possibility of earthquakes in this area in a certain period of time in the future, divide the dangerous areas and predict the possible losses after the earthquake. Since 1970s, great progress has been made in the study of earthquake preparation process and precursor mechanism. For example, the United States and the former Soviet Union put forward expansion-expansion model and avalanche-instability model, and China put forward source combination model and expansion-creep model. Wu Lixin et al. [6 ~ 7] took fault stick-slip as the simulation object, and used biaxial loading experimental system and infrared thermal imager to simulate the temporal and spatial evolution characteristics of infrared radiation temperature field in the process of double shear stick-slip under the conditions of four types of fault combinations. The research shows that the temporal and spatial evolution of temperature field on fault plane is not only related to stress level, but also related to lithology and roughness on both sides of friction surface. The specific manifestations are as follows: ① the infrared radiation is strong in areas with strong stress concentration and friction; However, infrared radiation is weak in areas with weak stress relaxation and friction. (2) When the lithology and friction surface conditions of the two faults are symmetrical, the infrared thermal image is butterfly-winged; When the friction surface is rough, the infrared thermal image shows asymmetric and unbalanced temporal and spatial evolution characteristics, such as beaded, needle-shaped, inverted needle-shaped, strip-shaped, single butterfly-shaped or their sequential changes. Combining satellite thermal infrared remote sensing with differential interferometric radar (D-INSAR) technology, focusing on the pre-slip of active faults and its subsequent stick-slip, is expected to become a new way to monitor tectonic earthquakes and predict short-impending strong earthquakes by remote sensing. Although these studies explain the mechanism of earthquake preparation and precursors to a certain extent, due to the extreme complexity of earthquakes, various theories still cannot fully explain the characteristics of various precursor phenomena.
In the practice of earthquake prevention and disaster reduction, people gradually realize that earthquake prevention and disaster reduction involves all aspects of social and economic life and the lives of the general public, and it is a complex social system project. In order to effectively reduce earthquake disasters, on the one hand, under the leadership of the government, we should popularize earthquake science knowledge, raise the awareness of earthquake prevention and disaster reduction of the whole people, rely on the legal system and science and technology, mobilize and organize all forces, and make concerted efforts; On the other hand, researchers should devote themselves to the study of earthquake prediction mechanism and comprehensive prediction, and change from empirical prediction to physical prediction to improve the accuracy of earthquake prediction.
(2) Volcanic eruption [8 ~ 9]
There is a "liquid zone" under the crust 100 ~ 150 km. In this liquid zone, there are molten silicate substances containing gas volatiles at high temperature and high pressure, that is, magma. Magma rushed out of the surface from the weak part of the earth's crust and formed a volcano. Volcanic eruption is one of the most powerful natural phenomena on the earth, and the energy it releases is sometimes thousands of times larger than that of a nuclear explosion.
The substances ejected from the volcano include solid substances such as broken rocks, debris, volcanic ash powder, liquid substances such as molten rock flow, water and various mud flows, and gaseous substances such as oxides of water vapor, carbon, hydrogen, nitrogen, fluorine and sulfur, and sometimes visible or invisible light, electricity, magnetism, sound and radioactive substances are ejected, which will lead to death, failure of electrical appliances and instruments, etc. In the past 500 years, millions of people have died from volcanic disasters. The deadliest volcano in human history occurred on the Greek island of santorini in the European Aegean Sea from 65438 BC to 0470 BC. When the volcano erupted, it spewed out as much as 62.5 billion cubic meters of material, destroying a human civilization called Minos.
Although volcanic eruption is sudden, it also has its inherent regularity. Precursors are more obvious than earthquakes, so people can know in advance and escape. In order to predict volcanic eruptions more timely and accurately, scientists have made unremitting efforts and successfully predicted some volcanic eruptions. For example, in 1979, the United States set up an observatory around Mount St. hellens, which successfully predicted the volcanic eruption of Mount St. hellens.
(3) Landslide and collapse [10 ~ 1 1]
Landslide usually refers to the rapid sliding movement or falling of earth-rock or rock under the lubrication of gravity or water, which is a typical form of rapid block movement. Landslides will cause slope instability, and falling rocks will often destroy buildings on both sides of the road, bury houses, hinder traffic and other accidents, and even hit passing vehicles in serious cases, causing casualties.
Landslide is a serious geological disaster second only to earthquake and flood, which not only occurs in much greater frequency and breadth than earthquake events, but also causes huge losses, which will endanger people's lives and property. For example, the table 1. 1 shows the annual average number of landslide deaths in some countries and regions.
Table 1. 1 Average number of deaths and annual probability caused by landslides (end of 20th century)
In China, because 70% of the places belong to mountainous areas, the density and frequency of landslides are very high, so it has become one of the countries most seriously affected by landslides in the world. Up to now, the provinces and cities that have reported landslide disasters are: Nanjing, Xi, Baoji, Yan 'an, Chongqing, Lanzhou, Taiwan Province and Hongkong. With the rapid development of economy and the unreasonable development and utilization of land resources, the landslide problem that endangers human safety will become more prominent and serious. Therefore, it is of great practical significance to minimize the damage to geological environment, control slopes, prevent landslide accidents and reduce the losses caused by landslide disasters to people's lives and property.
(4) Coal and gas outburst [12]
Coal and gas outburst is a kind of coal-rock dynamic disaster phenomenon, in which the coal-rock mass containing gas moves rapidly from the coal-rock mass to the mining space under the pressure, accompanied by a large amount of gas emission. The phenomenon of coal and rock dynamic disasters is also the main research object of this book.
According to the mechanical characteristics of dynamic phenomena, it can be divided into outburst, extrusion and dumping, and its main forces are geostress, gas pressure and gravity.
Classification according to the intensity of dynamic phenomena:
1) Small outburst: the intensity is less than 50 t/ time (after outburst, the gas concentration can return to normal in a few minutes);
2) Medium outburst: the intensity is 50 ~ 99t/ time (after outburst, the gas concentration can return to normal in one shift);
3) Secondary outburst: the intensity is 100 ~ 499t/ time (after outburst, the gas concentration gradually returns to normal above 1 day);
4) Big outburst: the intensity is 500 ~ 999t/ time (after outburst, the gas concentration can return to normal in a few days);
5) Extraordinary outburst: the intensity is greater than 1000 t/ time (after outburst, the gas concentration returns to normal after a long time).
This powerful dynamic disaster phenomenon poses an extremely serious threat to coal mine safety, especially to the lives and property of underground workers. The biggest outburst in the world occurred in the process of uncovering coal in the -7 10 m horizontal crosscut of Donbas Gagarin Mine in the Soviet Union in July, 1969. Outburst coal amount1.4000 t, and outburst gas amount is more than 2.5 million m3.
Coal and gas outburst in China is mainly coal and gas outburst. There have been more than 30 coal, rock and carbon dioxide outbursts in four mines, and the outburst phenomena in different regions have different characteristics. The biggest outburst in China occurred in1August 8, 975, and the No.6 coal seam was exposed by vibration blasting in the main adit of Sanhuiba No.1 Mine of Tianfu Mining Bureau, Sichuan Province. * * * The outburst coal and rock is 12780 t, and the gas is1.4000m3..
(5) rockburst [13 ~ 17]
Similar to coal and gas outburst, rockburst (also known as rockburst, rockburst or mine earthquake) is also a strong dynamic disaster phenomenon, but without the participation of gas, it is usually due to the rapid and violent release of energy gathered in coal and rock mass after the internal stress reaches a certain level, resulting in the destruction of coal and rock mass, as well as the destruction of supports, equipment and shafts, which will cause casualties in serious cases.
The recorded rockburst occurred in South Staffordshire Coalfield 1738, England. Since then, there have been many rockburst accidents in Germany, Poland, Canada, the former Soviet Union, Japan, France and China. The disasters caused by rockburst accidents in China are very serious. At present, there have been more than 4000 rock bursts in nearly 50 pairs of mines in China, causing hundreds of casualties and more than 30 kilometers of roadway damage.
Rock burst has three obvious characteristics: suddenness, instantaneous vibration and great destructiveness. According to the different stress state in coal and rock mass, rockburst can be divided into gravity rockburst, tectonic stress rockburst and intermediate rockburst or gravity-tectonic rockburst. According to the impact intensity, rockburst can be divided into ejection, mine shock, weak impact and strong impact. According to the intensity of magnitude and the amount of coal and rock thrown out of coal and rock mass, the rock burst is divided into three levels: slight impact (1 level, that is, the amount of coal and rock thrown out is below 10 ton, and the magnitude is also below 1) and moderate impact (level 2, that is, the amount of coal and rock thrown out is between 10 ~ 50t). According to the location and position of rockburst, it can be divided into coal body impact and surrounding rock impact.
The mechanism of rockburst is very complicated. Based on the field investigation and laboratory research results, scholars at home and abroad have studied it from different angles and put forward the following theories to explain the mechanism of rockburst: strength theory, stiffness theory, energy theory, impact tendency theory, three criteria theory and deformation system theory.
1. 1.2 coal and rock dynamic disaster mechanism
The mechanism of coal and rock dynamic disasters is very complicated, and many scholars have done a lot of work on its occurrence mechanism and prediction. Because this book mainly studies the electromechanical coupling of coal and gas outburst, rock burst and other coal and rock dynamic disasters, the following mainly expounds the mechanism of coal and gas outburst and rock burst.
(1) mechanism of coal and gas outburst [18 ~ 24]
Coal and gas outburst is an extremely complicated dynamic disaster phenomenon of coal and rock containing gas, and it is one of the main natural disasters in coal mine production. For coal and gas outburst and other coal and rock dynamic disasters, researchers all over the world are trying to understand the outburst mechanism and have made great progress. However, the continuous appearance of prominence shows that human understanding of prominence is far from perfect. Before Skoczynski and Khodot put forward the typical comprehensive outburst hypothesis, there were more than 100 kinds of outburst hypotheses, but in summary, there were mainly single-factor hypotheses such as gas-dominated hypothesis, ground pressure-dominated hypothesis and chemical essence hypothesis. So far, the hypothesis of chemical essence has not been supported in field observation and laboratory experiments, and has been abandoned by most researchers. However, the outburst hypothesis based on gas and ground pressure only explains the internal mechanism of outburst from one side, and there are many unexplained phenomena.
It is difficult to draw a clear timeline between the single factor hypothesis stage and the comprehensive hypothesis stage. Before and after Necrasov, a Soviet scholar, put forward the hypothesis of comprehensive action of ground pressure and gas in 1950s, various single-factor hypotheses appeared, while Necrasov's comprehensive hypothesis was not a classic comprehensive hypothesis. In fact, the comprehensive hypothesis should be marked by the comprehensive hypothesis put forward by Soviet scholar Sko Censky in the mid-1950s based on the experience of outburst coal seams and the scientific research achievements at that time. According to this hypothesis, outburst is the result of comprehensive action of ground pressure, gas contained in coal, physical and mechanical properties of coal, micro and macro structure of coal, coal seam structure and self-weight of coal. Since then, the famous scholar Huo Dollt has put forward the energy hypothesis of the comprehensive hypothesis, which makes the outstanding comprehensive hypothesis more perfect. Khodot and others from Censky Mining Research Institute of the former Soviet Union have done a lot of measurement and research on the pore structure, adsorption performance, permeability and mechanical properties of coal in the laboratory, and conducted simulation experiments of coal and gas outburst on the pressure testing machine. On this basis, the energy sources of coal and gas outburst are expounded. From the point of view of energy, the coal seam change situation, kinetic energy of surrounding rock, gas expansion work and the work needed to cause outburst are calculated by mathematical method, and the energy hypothesis is put forward. Since the advent of the energy hypothesis, it has greatly promoted outstanding research, and most of its viewpoints still have guiding significance today. The main disadvantage of the comprehensive action hypothesis represented by Khodot is that it does not explain the detailed failure process and failure conditions of gas-bearing coal, and does not consider the role of time factors in outburst, so it cannot explain the phenomenon of self-uncovering and delayed outburst of crosscut. Although various comprehensive hypotheses were put forward before and after the energy hypothesis, such as Bob Love's hypothesis of uneven stress distribution by Macheyev Security Institute of the former Soviet Union, and the dynamic effect hypothesis put forward by British scholars Pooley[ 19] and Farmer[20], they are all similar, and their similarity lies in that the outburst is the result of the comprehensive action of three factors: gas, geostress and physical and mechanical properties of coal. What's their difference? Like Khodot's comprehensive hypothesis, they all ignore the influence of time factors on outburst without exception, and fail to explain the failure process and specific conditions of gas-bearing coal bodies. They can't explain the natural outburst phenomena such as self-uncovering and delayed outburst. Jiang et al. of China University of Mining and Technology [2 1] made an experimental study on coal and gas outburst in the process of uncovering coal in crosscut, and put forward the spherical shell instability hypothesis of coal and gas outburst mechanism. Zhang [22] studied the technology of three-dimensional seismic detection of gas outburst danger zone, and applied it and verified it in Pansan Mine, Huainan. The research results show that high-resolution 3D earthquake can detect small faults with a drop of more than 3 m and small folds with corresponding amplitude, and faults and folds can cause structural stress concentration, coal destruction, gas accumulation and outburst, and gas outburst danger areas can be divided through quantitative evaluation of fault destruction and fold deformation. The application of three-dimensional seismic technology to detect the dangerous area of gas outburst has broad application prospects.
In the research process of coal and gas outburst and its mechanism, many methods are adopted, but in summary, there are mainly observation statistics, logical deduction, experiment, numerical analysis and numerical simulation. The early understanding of the prominent mechanism was mainly based on observation and statistics, supplemented by logical deduction, or the synthesis of these methods. The understanding of outburst mechanism depends on the depth and breadth of observation. The complexity and non-repeatability of salience make observation statistics very difficult, so the salience mechanism based on personal observation statistics inevitably has some one-sidedness. With the accumulation of observation statistics and the development of laboratory experiments, people gradually understand the prominent contour. Coupled with the progress of related disciplines (such as rock mechanics, rock fracture mechanics, rheological mechanics) and the application of high technology (such as scanning electron microscope, computer technology, etc.). ), based on a large number of excellent examples and experiments, combined with numerical simulation technology and new laboratory results, the researchers put forward a more perfect excellent mechanism, and excellent rheological mechanism is one of them.
However, most of the above assumptions are based on mechanics, and the detailed deformation and fracture process of gas-bearing coal and rock materials are rarely considered, which is the main reason why the research on coal and gas outburst can not be further carried out at present. Gas-bearing coal rock is a typical heterogeneous medium composed of porous solid skeleton composed of coal and rock particles with uneven spatial distribution, free gas in pores and quasi-liquid adsorption layer on pore surface. The behavior and behavior of this medium can't be fully and truly described by any single theory. For example, solid mechanics or rock mechanics generally use pure mechanical theory to study the behavior and properties of solid porous media such as coal and rock, and mainly adopt the effective stress principle of pure mechanical action when considering the action of pore fluid; Fluid mechanics or seepage mechanics mainly studies the law of fluid migration in pipe holes or fractures, regardless of the role of solids.
A large number of practical phenomena and experimental results show that the behavior change and movement process of gas-bearing coal and rock, a special three-phase medium, is a comprehensive action of mechanics (rock mechanics and rock fracture mechanics), physics, surface physical chemistry, electrodynamics, acoustics, thermodynamics, heat transfer and seepage mechanics, which is essentially different from single-phase or two-phase media. Therefore, it is necessary to combine macro and micro to describe and reveal the nature and dynamic disaster process of gas-bearing coal and rock, a special medium, across the above disciplines or theories.
Generally speaking, coal rocks and various concrete buildings under natural conditions belong to the media containing pore fluid, but usually, people ignore the role of pore fluid and simplify it into single-phase or two-phase media. In addition, this simplification allows a small deviation. However, the essence of this simplification is contrary to the actual situation, especially in the case of active pore fluid and high pressure, simplifying treatment will lead to wrong understanding results. Therefore, studying the dynamic disaster process of gas-bearing coal and rock plays an important role not only in understanding the disaster mechanism and rockburst mechanism of coal (rock) and gas outburst, but also in understanding and revealing the mechanism of earthquake and landslide, and evaluating the stability and life of large concrete dam foundations and high-rise buildings.
The theoretical basis of preventing and controlling outburst disasters is outburst mechanism, and the comprehensive hypothesis of coal and gas outburst has been widely recognized. It is considered that outburst is the result of the comprehensive action of in-situ stress, gas and physical and mechanical properties of coal. However, due to the outstanding complexity and limitations of research methods, there are insurmountable difficulties in outstanding laboratory simulation and field observation. We haven't fully understood its mechanism, so we can't accurately predict and monitor outburst, and we can't fundamentally explain the harm caused by outburst. Therefore, it is urgent to adopt new methods and means to study dynamic disasters such as coal and gas outburst.
(2) Mechanism of rockburst [25]
For a long time, rockburst, as one of the main problems in rock mechanics, has been concerned by academic and engineering circles at home and abroad. The mechanism of rockburst is also very complicated, and scholars at home and abroad have conducted a series of studies on it on the basis of field investigation and laboratory research. Its mechanism can be summarized as the following theories.
strength theory
Strength theory holds that when stress concentration occurs around the stope and the stress reaches the strength limit of coal (rock), coal (rock) is suddenly destroyed, thus forming rockburst. Modern strength theories, such as vault theory and cantilever beam theory, put forward at the end of 1930s all take the "ore body-surrounding rock" system as the research object, and hold that the bearing capacity of coal (rock) should be the strength of the "coal-surrounding rock" system, and the decisive factors leading to the failure of coal (rock) are: ① stress value; (2) The ratio with the strength of rock mass. In 1970s, Brauner put forward the theory of coal (rock) clamping, and deduced the formula for calculating the ultimate compressive stress of coal.
Energy theory
The energy theory explains the mechanism of rockburst from the perspective of energy transformation. According to this theory, when the energy released by the "ore body-surrounding rock" system is greater than the energy consumed when its mechanical equilibrium state is destroyed, rockburst will occur. Scholars from all over the world have made unremitting efforts to this end. The following are some major achievements.
From the point of view of energy source, Petuhoff thinks that the energy generated by rock burst is composed of the destroyed coal (rock) accumulation energy and the elastic deformation energy of the adjacent coal pillar or coal (rock) layer edge. The theory of residual energy was put forward by Americans in 1970s, and it is believed that the existence of residual energy is the mechanical reason for the dynamic instability of surrounding rock.
From the perspective of energy criterion, Brauner put forward the energy criterion of rockburst in 1970s, which considered the correlation between energy release and time when rockburst occurred, but did not consider the spatial effect of energy release.
However, the study of energy theory needs further research work.
Stiffness theory
The stiffness theory was originally obtained by Cook and others according to the rigid pressure theory. The theory holds that the rigidity of mine structure is greater than that of mine load system, which is a necessary condition for rock burst. In recent years, Petuhoff further defined the rigidity of mining structure as the rigidity that decreases after the stress-strain curve reaches the peak strength.
Impact tendency theory
The theory of impact tendency was put forward by scholars in Poland and the former Soviet Union. Impact tendency refers to the inherent property of coal and rock that produces impact failure, and it is a necessary condition to produce impact ground pressure. Through a lot of research, Chinese scholars put forward an experimental method to comprehensively judge the impact tendency of coal and rock with three indexes: elastic energy index, impact energy index and dynamic failure time of coal and rock. The theory of roof impact tendency is also reflected in the study of roof impact tendency, including roof bending energy index and coal seam impact caused by roof fracture under longwall mining method.
In addition, some progress has been made in the research of test methods, data processing and comprehensive evaluation.
theory of stability
In the mid-1960s, NevilleCook first applied the stability theory to study rockburst. Later, Lippmann put forward the "basic theory", and Zhang put forward the theory of rockburst instability, which was initially applied in practice.
Bazant and others analyzed the energy dissipation and scale effect caused by near-wall crack propagation, which made it possible to estimate the energy of rockburst. Zhang Xiaochun and others discussed the formation and failure mechanism of surrounding rock loose zone near coal mine roadway. Through theoretical analysis and experimental simulation, the structural instability model of coal mine spalling rock burst is established.
In addition, the bifurcation theory and catastrophe theory of material failure, which have developed rapidly in recent years, have also made some progress in the study of rockburst mechanism.
Generally speaking, rockburst is an unstable phenomenon caused by crack propagation and deformation localization, which is closely related to the mechanical properties of anisotropic coal-rock medium with cracks and the evolution and instability of stress-strain field of surrounding rock under load.