Discussion on the characteristics of debris flow in mine safety and disaster prevention and reduction

There are differences between the formation mechanism and evolution process of the debris flow in the mine and the natural debris flow. The systematic research on the debris flow in the mine is still in the initial stage, and the research results are few. The research summarizes the formation conditions and disaster characteristics of mine debris flow, and has important scientific research significance and practical application value for disaster prevention and reduction of mine debris flow. Mine debris flow is one of the most common and most serious types of geological disasters in mines. Unreasonable discharge of waste rock slag during the development of mineral resources is the main solid source of debris flow in the mine. The waste rock type debris flow and tailings type debris flow are the most important type of debris flow in the mine. Mine debris flow is characterized by humanity, frequent occurrence, and pollution controllability. Conduct investigation and evaluation of mine debris flow hazard ditch, study the formation mechanism of mine debris flow, implement the “disaster assessment” and “plan” compilation system of new mines, implement the reduction production and resource utilization of waste slag, select solid waste residue storage and discharge sites, and do Good measures such as slag retaining measures and comprehensive treatment of mine debris flow can avoid the occurrence and damage of debris flow.

First, the mine debris flow and its harm

(1) Conditions for formation of mudslides in mines

Mine debris flow is a kind of geological disaster unique to mountainous areas, which is often the result of the combination of natural factors such as structure, topography, meteorology and hydrology, vegetation and human engineering activities [5]. The formation conditions are the same as the general debris flow, and must have three basic conditions: high and steep topography, heavy rainfall or other hydrodynamic excitation conditions and abundant and loose solid source. Therefore, the mountainous hilly area is inevitably a prone area of ​​debris flow. In addition to our oil and gas, brick clay, the vast majority of metal minerals, non-metallic minerals produced in the mountains, so is mine debris flow in mountain terrain with elevation, due to the development of mineral resources caused mudslides and increased labor under heavy rainfall conditions. During the mining activities such as mine road construction, industrial site construction, mining and mineral processing , the discharged waste rock and tailings sand provide abundant and loose solid materials for the formation of mine debris flow. The mine debris flow becomes the most common and most harmful in mountainous areas. One of the types of geological disasters.

Although the formation, movement and accumulation process of the mine debris flow have the common characteristics of natural debris flow, the biggest difference from the natural debris flow is the different sources of solid phase materials that constitute the debris flow. The source of debris flow in mines mainly comes from waste rock waste slag discharged during the development of mineral resources. It is artificially accumulated and has a high accumulation rate and concentrated accumulation. It represents a continuous accumulation process for several years or even decades, and its scale depends on minerals. The intensity and scale of resource development activities; the source of natural debris flow depends on natural processes, the rate of formation of material sources is relatively slow, and the supply is relatively dispersed (except for the source of landslides and landslides). The scale depends on the surface erosion and gully erosion. strength.

The exploitation of mineral resources unreasonably piled up waste rock slag on the edge of the ditch brain, slope surface and gully river channel, crowded the ditch bed, blocked the river channel, caused poor flooding, increased the longitudinal slope ratio of the ditch bed, and provided for the formation of debris flow. The abundant loose materials exacerbate the occurrence, development and harm of the mudslide in the mine, leading to the non-deli flow or low-frequency debris flow before the mining development becomes a debris flow ditch or evolve into a high-frequency debris flow ditch; or the ditch itself before the mine development is the debris flow Ditch, mining development waste rock slag stacking has increased the occurrence and development of debris flow. The mine debris flow referred to in this paper refers to the artificial debris flow caused by the accumulation of waste rock slag in mineral resources development [8], including the formation of waste rock debris flow and tailings slag.

(2) Types of mine debris flow

Debris flows include natural debris flows and artificial debris flows according to their formation factors. Due to the formation, development and extinction process of mine debris flow, it is always carried out under the mineral resources development activities, so it belongs to the category of artificial debris flow or artificial debris flow [1-3]. The “artificial debris flow” may include debris flows formed by various activities of human beings, such as water and hydropower projects, mountain town construction, and traffic construction.

According to the type of solid phase material provided during the development of mineral resources, the mine debris flow can be divided into a waste rock type debris flow formed by waste rock discharged during the mining process, a tailings type debris flow formed by tailings sand discharged during the beneficiation process, and a mine. A landslide-type debris flow formed by collapsed landslide deposits. The scale and frequency of the debris flow in the mine depends on the amount of waste discharged during the mining activities and the continuous stacking time. According to the fluid properties after the formation of debris flow, the debris flow can be divided into viscous debris flow, transitional debris flow and dilute debris flow; the nature of waste slag discharged by mining and particle gradation determine the type of mine debris flow. Composed of solid phase materials, the mine debris flow can be divided into water stone flow, mud flow and mud flow. The mine water and rock flow is mainly formed in the mining areas related to the distribution of granites , carbonate rocks and hard metamorphic rocks, such as the Xiaoqinling gold deposit; and in the sedimentary rocks such as mudstones and sandy mudstones, as well as schist and phyllite. soft metamorphic rock lithology mine, for the mudflow, mining spoil Shenfu coal mine field mainly siltstone, mudstone, so the formation of debris flow [7].

According to the landform form of the debris flow formation site, the mine debris flow can be divided into a hillside type (slope surface) debris flow, a valley type debris flow and a valley type debris flow. In the excited hydrodynamic conditions, the mine debris flow can be divided into precipitation-type debris flow, ice-water melt-type debris flow and collapse-type debris flow (reservoir, tailings pond, dammed lake, alpine icy lake, collapse landslide blockage valley channel, etc.). Precipitation-type debris flow is the focus of mine disaster prevention and mitigation.

(3) Mine debris flow hazard

The mudslide is characterized by its sudden outburst, strong momentum, strong impact, large volume of scouring and silting, and high speed of mainstream swing. It shows great harm by scouring, impact and siltation. Because the mountain areas where the mine is located are mostly narrow and long valleys, the mining industry sites and personnel are mostly distributed in the area where the mudslide flows through the mine. Therefore, after the occurrence of the mudslide in the mine, it often causes heavy casualties and economic losses of the mine (Table 1, Table 2). Some of the waste rock-type debris flow disasters in our country's history are shown in Table 1.

The tailings pond is one of the important industrial facilities of metal mines. Due to the limited terrain conditions in the mountains, the construction of valley-type tailings ponds is often difficult to avoid residential areas. Therefore, once the mine tailings pond breaks the dam, the tailings containing a lot of water are along the valley. It is dumped downstream to form a sediment flow, causing a major disaster in the group. The research of the pollution assessment team of Clark University in the United States shows that the damage of the tailings pond dam accident is ranked 18th among the 93 accidents and pollutions in the world, second only to nuclear explosions, nerve gas, nuclear radiation and other disasters. Other 60 kinds of disasters such as aviation crashes and fires are serious. The tailings-type debris flow formed by the tailings pond dam that directly caused more than 100 deaths is not new (see Table 2).

Second, the characteristics of mine debris flow

Mine debris flow, like natural debris flow, has a diversity of formation types, which can also cause disastrous consequences for group deaths. However, due to the influence of the man-made activities of mineral resources development during the formation and evolution of the debris flow in the mine, the mine debris flow also has different characteristics of general debris flow.

(1) Humanity

Under the condition that the basic conditions of the debris flow and the rainfall formation in the original valley are unchanged, the occurrence and evolution of the debris flow in the mine is controlled by the human activities of mineral resources development. Loose earth and rock deposits discharged from mining increase the longitudinal slope ratio of the gully in steep and narrow gullies that are easy to collect water. In the absence of effective slag blocking, stable slag retaining and drainage engineering measures Underneath, artificially providing abundant loose materials for the occurrence of debris flow, the original non-debris flow ditch or low-frequency debris flow ditch evolved into a debris flow ditch or a high-frequency debris flow ditch, which aggravated the occurrence, development and harm of the debris flow.

(2) Frequent

In the case of terrain elevation, vegetation cover, rainfall and other conditions, the activity of the debris flow ditch is controlled by the degree of solid material recharge. Usually, after a natural debris flow occurs, the original material is transported out of the catchment area. The formation of the debris flow source in the valley requires decades or even hundreds of years, and it is difficult to form a debris flow in the valley [12]. However, in the mine, once a mudslide has passed, as long as the mining activities do not stop, the waste rock slag of the mining will continue to accumulate in the gully slope continuously, providing a new source of debris for the recurrence of the debris flow. In addition, the cohesive force and internal friction angle of the mining waste rock slag are small, and the impact resistance is weakened. Under the influence of mining blasting, mining earthquake, mining collapse, earthquake, etc., the limit of rainfall that causes the formation of the debris flow is reduced. Therefore, mountain mines become a prone area and frequent occurrence of mudslides. For example, there are 23 mudslides in the same mine in the northwest region, 7 in 3 times, and 4 in 4 times. Ningxia Yugou Coal Mine had successively caused mudslides in 1997-08-13, 1998-05-20, 2002-06-07, resulting in a total of 8 deaths, direct economic losses of 40 million yuan, 2.4km flood levees destroyed, along The high-voltage line poles on both sides of the ditch are all dumped, 293.33hm2 [8].

(3) Pollution

The waste rock, lean ore and tailings slag discharged from mountain metal mines usually contain heavy metal elements such as mercury , lead , cadmium , arsenic , copper and zinc . Therefore, waste rock slag type debris flow, especially tailings sand type debris flow, In addition to the disaster-causing effects of mudslides, such as scouring and burying, it also pollutes rivers, causes pollution of water sources, and causes major social problems.

(4) Controllability

Because mine waste rock slag and tailings sand are the main loose materials that cause the formation of debris flow in the mine, the location and quantity of the mine are determined, that is, the location of the formation of the debris flow is clear, and the endangered object is the downstream circulation area and accumulation area of ​​the area. Mine facilities and personnel within. Therefore, the difference from the general debris flow is that the prevention and control of the mine debris flow is focused on source prevention. Select reasonable slag yards, construct engineering measures such as slag stabilized slag retaining wall and waste slag drainage and drainage; control the stability of the mountain in the subsidence area, and reduce the collapse and landslide deposits as the source of debris flow. By controlling the source of the debris flow in the mine, it is possible to control and mitigate the occurrence of mine debris flow and its disaster losses.

3. Temporal and spatial distribution of debris flow in mines in China

By the end of 2005, the survey of mine geological environment in 31 provinces and autonomous regions in China [13-15] showed that between 1958 and 2005, 609 waste rock-type debris flows occurred in mines in China (excluding tailings-type debris flow), causing 680 deaths. Among them, there are 59 large and large debris flow geological disasters, 447 medium-sized and 105 small. Among the 609 mine debris flows, 923 mudslides occurred in 9,764 metal mines, accounting for 33.3% of the total number of mine debris flows, with an incidence of 20.8 ‰; 26,125 coal mines occurred 231 times, accounting for 37.9% of the total. 8.8‰; 169 times of debris flow occurred in non-metallic mines, accounting for 28.6% of the total, with an incidence of 2.3%.

Figure 1 shows that the number of occurrences of mine debris flow in China has increased significantly since 1994, with an average of more than 10 times per year. Especially since the beginning of the 21st century, the annual mudslides in the mines have been more than 30 times per year, reaching an extreme value of 58 times in 2004. After the mid-1990s, the phenomenon of large mines opening and opening of a mine was prominent. The number of mines increased sharply, waste slag was discharged at will, vegetation was destroyed, soil erosion was intensified, and the ecological environment of mountain mines deteriorated drastically. As a result, the mudslides in mines showed a high incidence. Typical, such as the Xiaoqinling gold mining area, after the disappearance of hundreds of slag-type debris flows in 1994, the subsequent occurrence of waste rock-type debris flow in the mining of several gold mines such as Dongtong, Shaanxi, and Dahuyu, Henan. . The investigation shows that the 18 ramps in the Xiaoqinling gold mining area are caused by the accumulation of waste rock slag, which forms a hidden danger of mudslides, and the hazards of mudslides are becoming more and more serious [14,15].

Figure 2 shows that the mountainous and hilly areas such as the Chinese and Western Tianshan Mountains, the Qilian Kunlun Mountains, the Helan Mountains, the Qinba Mountains, the western Sichuan Plateau, the Yunnan-Guizhou Plateau, and the southern Hunan and southern Guangdong are the high-prone zones of the mines in China. This is consistent with the distribution of regional debris flow high-prone areas in China, that is, in the mountainous areas where mudslides occurred, mineral resources development activities have intensified the occurrence and harm of debris flow.

Fourth, the research status of mine debris flow

(1) Research status of debris flow at home and abroad

The study of debris flow began in the middle of the 19th century. Before the 1930s, the study of debris flow was dominated by line survey and macro-engineering prevention; from 1930 to 1970, it was the understanding of the distribution law of debris flow, the establishment of observation stations on the ground, and the accumulation of observation data; from the 1970s to the 1990s, it was a debris flow model. The experimental and artificial debris flow test is the research period of the debris flow dynamics and kinematics mechanism of the research method; since the 1990s, it is a new era of comprehensive prediction and forecasting of the debris flow system and comprehensive management, with multi-disciplinary, multi-directional and multi-method observations. And model tests were conducted.

The formation of debris flow is the core issue of debris flow research and the theoretical basis for debris flow disaster prevention. The scientific and rational debris flow control plan and disaster mitigation technology are based on the correct understanding of the formation of debris flow [12]. Due to the complex factors affecting and controlling the formation, movement and accumulation process of debris flow, the research on debris flow at home and abroad needs to be further explored and improved. The understanding of the different stages and processes of the debris flow from the beginning to the end is not enough. Risk assessment, forecasting, treatment and hazardous zoning of debris flows are not very effective.

(II) Research content and direction of mine debris flow

The study of mine debris flow is within the scope of debris flow research. Its formation conditions, occurrence and accumulation process have a special aspect in addition to its commonality. Therefore, in addition to inheriting the research content and methods of traditional debris flow, the study of mine debris flow is more important to increase the content of artificial geological and mine geological environment protection, organically combine natural and human factors, and develop mineral resources and geological environment. Organic combination, highlighting the application value of mine debris flow research. So far, the attention of mine debris flow research is far less than that of natural debris flow, which is at a low level of research, insufficient depth and systematic lack of [16]. Therefore, the study of mine debris flow is based on regional geological environment survey, mine debris flow ditch observation, formation model (concept model, physical model, mathematical model), formation mechanism, monitoring and forecasting, risk assessment and comprehensive prevention, and adopt information acquisition method. Field field observation method, simulation experiment method, mathematical model method and comprehensive analysis method are used to carry out investigation and research on mine debris flow. It is necessary to focus on the following aspects:

1. Characteristics, formation conditions and distribution rules of mine debris flow;

2. The mining debris flow disaster and the disaster (risk) assessment;

3. Formation mechanism of mine debris flow;

4. Mine debris flow prevention technology and its mode;

5. The law and prevention mode of tailings sand and debris flow.

V. Countermeasures for disaster prevention and mitigation of mine debris flow

Since the mine debris flow belongs to the category of man-made debris flow, the biggest difference from the natural debris flow is the difference in source of the source. However, once the mine debris flow occurs, there is no big difference between the prevention technology and the natural debris flow. Therefore, to control and reduce the occurrence of debris flow, the focus is on prevention from the source, the key links and key technologies are to control the number of solid phase sources formed by the debris flow in the mine, the accumulation site and its stability, and the stability of the goaf and its slopes. Reach the accumulation of landslides and landslides.

(1) Investigation and evaluation of hidden debris flow in mine debris flow

Due to historical understanding, China's mountain mines lack effective geological environment prevention and control work. Therefore, there are serious mudslide disasters and hidden dangers in the mines. At present, the investigation and evaluation of mine debris flow has not been systematically carried out, which has restricted the active prevention of mudslides in mines. Select regional high-flow areas of debris flow, carry out investigation and evaluation of distribution, scale, type and hazard of mine debris flow, analyze and study the main factors affecting the formation and development of mine debris flow, and provide basic information for disaster prevention and mitigation.

(II) Theoretical study on prevention and control of debris flow in mines

The research on the initiation mechanism of the debris flow in the mine is carried out to study how the slag reactor is started and its critical conditions, movement and accumulation process, etc., to provide a basis for the meteorological prediction of the mine debris flow. For the hidden dangers of mudslides in major mines that seriously threaten the mining production and the ecological environment of human settlements, the rainfall warning and forecasting work will be carried out.

(3) Implementing “disaster assessment” and “plan” to prevent the formation of mudslides from the source

The mining enterprises shall conscientiously implement the geological disaster risk assessment of the construction project, avoid or treat the original debris flow ditch in the stage of mine industry layout, select the mine waste rock waste slag stacking position in the mine construction and production process, and do a good job of guarding measures. Avoid waste rock waste slag from the source to become a debris source. Implement the mine geological environment protection and restoration and control plan, and control the waste rock pile while mining.

(4) Reduced production and resource utilization of waste slag to reduce solid matter forming mine debris flow

Optimize the mining plan, implement the reduced production of waste rock waste slag, or waste rock waste slag without pits, less pits, and dumping technology in open pits. At the same time, according to local conditions, resource utilization of waste rock waste slag and beneficiation tailings, such as road construction, wall bricks, floor tiles and other materials, can improve the comprehensive utilization of mineral resources and economic benefits, while reducing the amount of waste rock waste. Achieving a source of reduced debris flow in the mine.

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