Mine Geological Safety - Mine Geological Environment and Geological Hazards
Mine geological work is an indispensable basic technical work in mining. It refers to the geological work directly for production in the production area or mining area of ​​the deposit in the mining process, according to the needs of the mine work. The geological work of the mine geological work Based on the project of mine mining activities, it is the technical basis and basis for mining production and management activities. The mining activities must be moved with the advancement of mining operations. There is no fixed working space and place, and the working environment conditions are greatly affected by engineering geology and hydrogeological conditions. Therefore, in order to ensure the smooth progress of mining activities, it is necessary to understand the impact of mine geological structure, hydrogeology and rock properties on mine safety.
Mine geological environment and geological disasters
Environmental geological problems refer to geological disasters caused by human beings engaged in technical and economic activities or natural factors. The environmental geological problems brought about by human beings in the process of exploiting and utilizing mineral resources are becoming more and more obvious and increasingly serious. Currently, the total annual human exploitation of mineral resources exceeds 1.0 × 10 11 t, of which 50% to 60% coal, 85% iron, 85% to 90% of the metal deposit 50% of the chemical raw materials mining, 100 % of non-metallic and building materials are open-pit mining, resulting in extremely large mine stripping. With the sharp decline of surface mineral resources, the exploitation of mineral resources is becoming more and more deep, and the impact on the environment and the depth and breadth of damage are increasing. Due to huge mining engineering activities, various environmental geological problems, such as soil erosion, landslides, collapse, subsidence of ground subsidence, mine heat damage, induced earthquakes, polluted water bodies and air, cause huge losses to people's lives and property.
I. Surface environmental geological problems caused by mining
(1) Destruction of landscapes and reduction of cultivated land area Whether it is open-air or underground mining, the destruction of the landscape by the mining engineering activities is very significant. Large areas of land are occupied, trees are cut down, vegetation and soil are destroyed, rocks are exposed in large areas, water and soil are largely lost, and rivers are diverted. With the continuous expansion of the tailings pond area and the gradual drying up of the tailings pile, the degree of desertification of the land has also increased. About 90% of China's metal mines are open-pit mining. The annual stripping of rock and soil is about 2.2-260 million tons, which is one of the important factors causing soil erosion, vegetation damage, and even desertification disasters.
(2) Disasters caused by accumulation of waste ore and meteorites The accumulation of waste ore, vermiculite and tailings extracted underground or in the open air is increasing, and the degree of deterioration of the geological environment has been reached. At present, China's coal mines discharge nearly 200 million tons of vermiculite per year, plus more than one billion tons accumulated over the years, the number is quite large, occupying large areas of land and farmland. Waste ore and vermiculite are disposed of for a long time, causing weathering and spontaneous combustion. The temperature can reach several hundred degrees, and a large amount of harmful gases such as H 2 S, SO 2 , CO 2 and dust are generated, which pollutes the air. Atmospheric precipitation seeps into the waste rock pile, dissolves some harmful chemicals, and then discharges it into surface water bodies and infiltrates into the groundwater of the soil, causing the water body to be contaminated. The groundwater mineralization, hardness increases, soil salinity increases, causing nicotine, causing crop growth. The development was severely hindered, and part of the mining area was abandoned. China's metal mines discharge about 200 million tons of tailings each year. In order to reduce the land occupation and solve the increasingly tense land use contradiction, the construction height of tailings dams is increasing. When the rainy season or heavy rains occur, the dam break becomes a major hidden danger in the mine. In addition, surface waste ore and meteorite accumulation can also cause environmental hazards such as collapse, landslides and mudslides.
Second, environmental geological problems caused by open pit mining
As the depth of open pit mining increases, the scale of the slope also expands, which not only seriously destroys the natural balance of ground stress, but also causes the deformation, damage and slip of the artificial slope. The form of its destruction is mainly collapse and landslide.
(1) Collapse Collapse is a form of destruction in which the slope rock mass moves rapidly under the action of gravity, suddenly collapses and accumulates at the foot of the slope. It can occur on the slope of an open pit or on a steep slope of a mountain. For example, China's western Hubei Salt Lake River phosphorus ore giant landslides occurred, its accumulation body thickness of 20m, the most thick 38m, accumulation of earth and stone of 106 m 3, caused huge casualties and property losses.
(2) Landslide A landslide is another form of failure in which a local rock mass of a slope slides along a plane or a curved surface as a whole. In addition to the structural conditions of the slope rock mass and the geological environment (such as atmospheric precipitation, weathering and earthquake action), the factors affecting the instability of the open slope are mainly human induced factors. For example, an unreasonable stripping ratio causes a landslide. The lower the stripping ratio, the larger the slope angle, and the total slope angle of a large open pit mine increases by 1°, which can reduce tens of thousands of tons of rock-peeling and save tens of millions of yuan. However, the steep slope of the slope often causes creeping deformation of the slope, leading to major landslide accidents. The open-pit blasting vibration not only increases the sliding of the slope, but also destroys the rock mass of the slope, reduces the strength of the rock mass, makes the rainwater and groundwater easy to penetrate along the blasting gap, accelerates the weathering of the rock mass, and reduces the stability of the slope.
3. Environmental geological problems caused by underground mining
The environmental geological problems caused by underground mining are mainly the collapse of goaf and geothermal hazard.
(1) Collapse of goaf After a large area of ​​underground ore body is mined, the balance is destroyed due to the loss of support of the upper layer, resulting in bending and slumping, which leads to the deformation and collapse of the surface. For example, Hunan Tin Mine is an underground mine that has been mined for hundreds of years. The mining depth is 300-400m. There have been many underground roof accidents. In 1971, large-scale ground pressure activities occurred. The volume of the empty area reached 2.274 million cubic meters, and the underground fell 16.9. Ten thousand cubic meters, making the surface move by 794,000 cubic meters.
Due to human activity mining, tunnel destroyed top, bottom slate stone stability, reduces the strength of rock tunnels, produce a series of band gap or weak, and provides an important way for a variety of water-filled flow channels into the mine. When these cracks or passages communicate with the overlying aquifer or surface water body, or because the top and bottom of the tunnel with reduced strength cannot withstand the pressure of the surface (or underground) water body, it will cause sudden flooding of the mine and cause underground flooding. China's coal mines and metal mines have occurred in floods, causing serious casualties and economic losses. For example, 81 people were killed in a large flooding accident in the Danlajiapo mine in southwestern Guangxi.
(2) Geothermal Geothermal is a geological phenomenon, and its heat source mainly comes from the heat released during the metamorphosis of radioactive elements and the heat released by the chemical reaction of elements. The temperature distribution of the rock below the surface is the variable temperature zone, the constant temperature zone and the warming zone. The temperature change zone is generally within 20m, and its temperature is greatly affected by surface changes. The temperature of the ground is generally about 20 to 30 m, and the temperature change is about 1 to 2 ° C higher than the local average annual temperature. Below the constant temperature zone is a warming zone, and the temperature of the rock formation increases regularly with increasing depth. Most of the earth's area is 100m deeper from the constant temperature zone, and the temperature rises by about 3 °C.
For mining work, geothermal heat causes an increase in the underground temperature of the mine, which is unfavorable for mining. Especially when the mining work enters a deep level, it is necessary to fully consider the geothermal factors, adjust the ventilation system in time, strengthen ventilation measures, improve working conditions, and take effective measures to properly use thermal energy.
4. Earthquake activity induced by mining
Earthquake-induced earthquake activity (also known as mine earthquake) is a kind of underground artificial induced disaster. According to its causes, mine earthquakes can be divided into induced tectonic ore-induced earthquakes, induced rockbursts on the working face, and rockburst induced by coal bursts.
(1) Induced tectonic ore-type earthquakes There are two types of induced tectonic ore-seismic earthquakes. One is the earthquake induced by the imbalance of underground stress caused by mining. The epicenter of this mine is located in the deep mining area, the source is very shallow and the magnitude is low. The second is the earthquake induced by mining pumping. Due to the water pressure before pumping, the fracture surface is infiltrated by water, and once the water pressure is lost, the pressure relief occurs along the fracture surface to form a bias stress, and when the stress is greater than the shear strength of the section, an earthquake is induced. For example, after the pumping and draining of the Endouqiao mining area in Hunan, 16 earthquakes occurred.
(2) Induced collapse-type ore-induced earthquakes Most of the induced earthquakes in the mining area belong to this type and are caused by the fall of the goaf or the roof. In the Datong Coal Mine in Shanxi Province, China, there were more than 40 earthquakes caused by the collapse of the roof between 1956 and 1980. During the mining of some karst water-filled deposits in southern China, due to a large amount of water pumping, drainage and drainage, causing tunnel collapse, there have been small earthquakes.
(3) Working face rockburst or coal explosion induced mining earthquake Mine mining face suddenly flies out like a bomb explosion, accompanied by loud noise, air waves and vibration, destroying the roadway engineering facilities or causing casualties. This phenomenon is called rockburst, also known as impact ground pressure. There have been many underground rockbursts in China. For example, Sichuan Mianzhu Mine has experienced many rockbursts in mining, and one of them has thrown more than 20 tons of coal 20m away.
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