I. Introduction
Coal is the main basis of our energy, conventional energy reserves in the country, accounting for more than 90% of coal resources, which determines China's coal-based energy production and consumption in large part. In the next 50 years, the main position of coal in China's energy structure will not change. Shanxi is the region with the richest coal resources in China. It has proven reserves of more than 260 billion tons of coal resources, ranking the first in the country with 26%. Shanxi coal has an annual output of 2.67 million tons from 1949 to 500 million tons in 2005. From 1979 to 2004, Shanxi Province produced a total of 6 billion tons of raw coal and exported 4.5 billion tons of raw coal. The raw coal production accounted for 25% of the national output. Although Shanxi Province has provided a large amount of cheap high-quality coal to the whole country, it has also caused huge ecological and environmental pollution, resource destruction and a series of undesirable social problems. According to reports, the current coal industry in Shanxi Province has accumulated collapse, destruction and coal gangue pressure has reached 66,700 hm2, and is increasing at an annual rate of 5000 hm2, of which 40% is cultivated land. In recent years, the state has attached great importance to the restoration of land development and used it as an important means to implement the “dynamic balance of cultivated landâ€. Based on the type of land destruction in the mining area, this paper proposes measures for land reclamation and ecological reconstruction in the mining area.
Second, the land destruction characteristics of the mining area
Shanxi is China's first coal-producing and coal-producing province. The advantages of coal resources are unique, with large reserves, wide distribution, complete varieties, excellent quality and easy exploitation. The province's coal-bearing area is 64,800 km2, accounting for about 40% of the province's total land area. Shanxi's coal geological structure is simple, shallow burial, thick coal seams, and few faults, most of which are suitable for underground mining.
(1) Mining damage to the terrain
Shanxi coal mines are mainly underground mining. Underground mining often causes deformation, cracks and even collapse of the formation, in addition to solid waste accumulation. The surface subsidence caused by coal mining can be divided into: according to its shape and degree of damage: 1. Funnel-shaped craters and stepped faults formed by shallow mining of steeply inclined coal seams or thick coal seams. These collapse pits often occur suddenly, and the plants above them Both the building and the building were damaged, causing damage that could not be prevented, but the collapse occurred only locally, although the damage was severe but the scope was small; 2. The steeply inclined coal seams in the deep mining and the coal seams with a depth ratio >20 and a dip angle of <450 occurred. In a gently sinking basin, this type of collapse is formed in an unconscious slow process. In general, the maximum depth of surface subsidence is about 70% to 80% of the thickness of coal seam mining, and even up to 90%. Usually, due to the various coal pillars left in the ground, their support to the stratum causes the collapsed area to have a complex shape with unevenness. The collapse volume is about 60% to 70% of the coal seam production volume, and the collapse area is the coal seam mining area. 1.2 times. Surface subsidence most direct and obvious damage is to make the building collapse on the area (including buildings, pipelines, railways, roads, bridges, etc.) and even deformation damage. According to statistics, the land subsidence caused by coal mining in Shanxi has reached 8,000 km2, of which the area of ​​the goaf is 5000 km2, and the area causing serious geological disasters reaches 2,940 km2. In addition, underground mining inevitably produces large amounts of solid waste, and most of it is piled on the surface to form a meteorite mountain. Although meteorites can generate electricity and are used as building materials and chemical raw materials, but limited to economic and technical reasons, the current utilization rate is less than 15%, and the meteorites used only account for 3% to 5% of the discharge.
(2) Mining damage to the soil
The damage to the soil caused by mining activities is mainly caused by soil erosion. In the natural state, the surface erosion process caused by natural factors is very slow, the performance is extremely insignificant, and it is often in a relatively balanced state with the natural soil formation process. However, mining activities, such as large-scale stripping, clearing of the ground, and handling of soil, stone, and slag deposits, will accelerate and expand the soil damage caused by natural factors and the movement and loss of soil materials. The soil erosion rate in the mining area is about 2000 times that of the same area forest area. Soil erosion in the mining area has caused land degradation and even desertification.
Mining activities damage to the soil in addition to producing soil erosion, but also lead to more heavy metals into the soil, the soil due to the adsorption, complexation, precipitation and retention and so on, the vast majority of residual heavy metals are accumulated in soil It can cause soil pollution, pollution and damage to plants, and reduce crop yield.
Third, land reclamation technology
In response to the above-mentioned mining damage to the land, in accordance with the requirements of the sustainable development concept, it is necessary to reclamation of the mining area and take remediation measures to restore it to a usable state.
(1) Technical characteristics
Land reclamation in mining area is a systematic and comprehensive system project involving geology, geochemistry, mineral deposits, mineralogy, mining engineering, engineering geology, environmental science, landscape ecology, agronomy, etc. The discipline therefore determines the complexity, breadth and diversity of the land reclamation technology in the mining area. The scientific mine land reclamation technology is to better integrate the advanced, mature and new technologies in various disciplines, and optimize the land use and ecological environment from a long-term perspective.
(II) Basic model of mine land reclamation
1. Engineering reclamation
Engineering reclamation refers to the use of mining equipment and mining technology in accordance with the requirements of the planned new land reclamation and land use status according to the planned terrain and geomorphology status of the abandoned land after mining, and the sequential refilling of the damaged land. Leveling, covering soil and comprehensive remediation, the core of which is land-building, creating a good ecological environment for the formation of bio-community in the bioremediation stage. Engineering reclamation can be divided into two forms: filling and non-filling reclamation. Combined with the direction of land reclamation and the form and extent of land destruction, the commonly used engineering reclamation techniques include: in-situ leveling, terraced leveling, deep-deep shallowing and filling method reclamation techniques.
2, biological reclamation
Bioremediation refers to various biological measures to improve and improve the productivity and environmental safety of reconstruction systems, among which bioengineering, ecological engineering and soil improvement technologies are very important. Bioremediation includes soil fertility and vegetation reconstruction. The core of the project is to quickly build artificial vegetation communities, that is, to establish artificial vegetation in the built ecological environment and form artificial communities. The key technology is to solve the problem of soil ripening and fertilization, and accelerate the restoration. The process of “raw soil†ripening:
(1) Soil fertility. It is through the adoption of various fertilization measures to accelerate the process of soil ripening in reclaimed land. The soil type on the surface is mainly through the application of organic fertilizer, inorganic fertilizer and planting green plants, so as to quickly establish the soil organic reservoir and nitrogen pool to achieve soil fertility; the surface soilless type generally uses weatherable mudstone and sandstone The mixed gravel is used as the soil, the proportion is adjusted, physical and chemical weathering is carried out in the air, and some special resistant plants are planted for biological weathering to achieve the purpose of soil ripening.
Microbial fertilization technology is a method of cultivating and improving poor soil by using microorganisms and chemical agents or a mixture of microorganisms and organic matter to restore soil fertility.
(2) Vegetation reconstruction. The restoration of vegetation can be achieved in two ways: 1 selecting or introducing pioneer plants with fewer restriction factors according to local site conditions, as plants grow, reproduce, and the environment gradually improves, while other plant species invade, eventually The succession is the climax community; 2 by artificially improving the site conditions, making it basically adapt to the growth of plants. Vegetation reconstruction should strengthen the maintenance and management of new vegetation, such as prohibiting grazing, deforestation and strengthening pest control.
(3) Land reclamation technology
The land reclamation technology for coal mining subsidence mainly includes:
1. Desalination method. It refers to the excavation of a large number of drains, so that the accumulated water in the subsidence area is drained, and necessary renovation works are carried out so that the subsided area no longer accumulates water and can be restored.
2, digging deep pad shallow method. Excavation machinery is used to deepen the deep collapsed area to form a water (fish) pond. The removed earth fills the shallow area of ​​the collapse pit to form cultivated land, achieving the purpose of aquaculture and agricultural planting.
3. Filling and reclaiming technology. Combine land reclamation with ecological engineering techniques, and comprehensively use theories of biology, ecological economics, environmental science, agricultural technology, and systems engineering to apply the principles of species symbiosis and material recycling in ecosystems. Multi-level utilization of process technology.
4. Ecological reconstruction technology in mining areas
The ecological reconstruction of the mining area mainly refers to the problem of land function degradation, ecological structure defect, dysfunction or degradation caused by mining. Through engineering, biological and other comprehensive measures to restore and improve the functions of the ecosystem, the sustainable development of the mining area is gradually realized.
(1) Technical characteristics
Its main features: 1. In the process of resource development in the mining area, try to avoid or reduce the damage to the land environment, and adopt an advanced prevention strategy, such as optimization of mining procedures and rational allocation of mining technology; 2. Abandonment or near closed pit mines Land ecological reconstruction, after some coal mines are closed, will leave a few hundred meters deep open pit, dozens of square kilometers of stope and dumping site, which has caused severe damage to the surrounding urban ecological environment, restricting the city's economy and society. Sustainable development requires urgently to rebuild a high-yield, high-quality, high-efficiency and sustainable development ecosystem in accordance with the laws of ecology and technology, and achieve symbiotic and coordinated development among population, land and natural environment; 3) ecological reconstruction of mining areas must be adapted to local conditions. Focus on the principles of comprehensive benefits and dynamic regulation.
(II) Engineering measures for ecological reconstruction of mining areas
1. Strictly plan the dumping site and tailings dam before mining
The dumping site is planned according to the topographical features within the mining area and the minerals, reserves and mining methods. The dumping site requires a place with a large mountain ridge, a narrow exit, a large amount of soil discharge, and stable geological conditions. The effective volume is about 40% more than the mining volume. The dump site must first set up a retaining wall to control soil erosion before vegetation restoration. The retaining wall should be reinforced and reinforced according to the shape of the dumping site and the amount of earth discharged each year. At the same time, the flood control trench should be repaired around the dumping site. The tailings dam must be included in the entire project budget and be constructed and inspected and put into operation at the same time as the main project to reduce the harm to downstream agricultural production and people's lives.
2. Slope protection levee project
Slopes of ancillary works such as stope steps, slopes and roads in mining areas shall be planned for slope protection to prevent landslides and collapses in the stope and roads. At the same time, the downstream of the mining area should also strengthen and raise the river dams and river embankments, and often clean up the silt stones deposited on the riverbed to prevent floods from dams, farmland, roads, bridges and houses.
3. Comprehensive utilization of tailings
The untreated or reused tailings not only occupy a large amount of land but also pollute the environment. Therefore, the comprehensive utilization and treatment of tailings is very important: 1) further recovery of valuable elements from waste, not only reduces costs, It can also reduce environmental pollution; 2) as a secondary resource to obtain new forms of substances, not only can harm to benefit, but also reduce the harm caused by toxic and harmful substances to humans; 3) use waste rock and tailings as underground mined Filling materials in the area not only save money, but also avoid land pressure and reduce the source of soil erosion.
4. Vegetation reconstruction engineering technology
Artificial vegetation is built on the built land according to social needs, forming an artificial vegetation community, and obtaining certain benefits after a period of time. Under the guidance of ecological theory, it combines the theories and technologies of various disciplines, promotes each other, regulates and controls, and makes overall arrangements. It mainly includes the screening and introduction of plants, cultivation and management of plants. Vegetation reconstruction in the mining area adopts a mode of rational allocation of grass, irrigation and arbor. The screening of general vegetation varieties is determined by laboratory simulation, on-site planting test, and empirical analogy. The selected varieties should grow fast, have high yield, good resistance to stress, and be resistant to poorness. Try to use good local varieties, and introduce fast-growing varieties when conditions are appropriate.
V. Conclusion
The destruction of coal resources is inevitable, but special attention should be paid to the coordinated development of the environment and the economy, and the legislative and law enforcement work on land reclamation and ecological protection should be strengthened. Adhere to the city's sustainable development strategy, strengthen ecological environmental protection while economic development, rationally and orderly use and protect the ecological environment, reduce the ecological damage caused by coal mining, and benefit future generations.
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