Generally speaking, the environmental geological problems caused by coal mining in northwest China are very serious, which is the most serious type of mine environmental geological problems among all mining types. Underground mining and open-pit mining have different effects on the geological environment of the mining area, and the environmental geological problems caused by underground mining are the most serious. Coal mines in northwest China are mainly underground mining, and its output accounts for about 96% of coal production. The main environmental geological problems are shown in Table 3-7. See Figure 3-3 for the schematic diagram of environmental geological problems in coal mining.
Table 3-7 Main Environmental Geological Problems of Coal Mining
Figure 3-3 Schematic Diagram of Environmental Geological Problems in Coal Mining
The open-pit mining of outcrop coal and shallow coal seam has changed the original landform: landslide (①) induced by high and steep slope, occupation of waste dump (②), landslide (①) caused by rainstorm on the slope of waste residue accumulation ditch, and debris flow (③). Ground fissures (⑥) above coal seam mined-out areas (④ and ⑤) will cause buildings to crack, farmland to be destroyed, ground subsidence above slightly deep coal seam mined-out areas (⑥), farmland to be destroyed and villages to move. At the same time, coal gangue accumulates and occupies land. At the same time, coal gangue dust and toxic and harmful gases produced by spontaneous combustion (⑧), methane and carbon dioxide emitted by wind wells pollute the atmospheric environment (⑨), which is harmful to human health. Surface water, soil (attending) and crop pollution are caused by open-pit mine dump and coal gangue leaching water, while groundwater and karst water pollution are caused by infiltration (attending).
3.4.2. 1 Coal gangue covers an area.
Coal gangue is the waste produced in the process of coal mining and coal preparation, which usually accounts for 12% ~ 20% of coal mine output. It is the most important solid waste in coal mine, and its main harm is to accumulate and occupy land and destroy vegetation. Huanglingdiantou, Shaanxi Province is located in the Loess Plateau, and the forest vegetation in the small watershed area is good, but some coal gangue discharged from coal mines accumulates on the hillside, occupying a well-grown miscellaneous forest. The Yellow River wetland in Xiayukou, Hancheng, Shaanxi has dense reeds and good ecological environment, but the coal gangue discharged from this mine fills the beach, which destroys the ecological resources and environment of the Yellow River wetland.
Influence of 3.4.2.2 on Water Resources
Carboniferous-Permian coalfields around Ordos Basin, with Ordovician limestone in the lower part and Jurassic sandstone and mudstone in the upper part, are serious water shortage areas in arid basins. Mine drainage leads to the destruction of groundwater balance system, the decrease of surface water volume and the decline of groundwater level. The acidic well water with high salinity in coal mine caused groundwater pollution, which aggravated the water crisis. The dip angle of coal measures strata in Liudaowan coal mine in Urumqi, Xinjiang is 67 ~ 78. After mining, mined-out collapse and broken zone are formed from top to bottom, which causes environmental damage of water resources loss. The continuous exploitation of coal resources in a large area has caused groundwater damage that is difficult to recover, and at the same time, it has led to a sharp drop in surface river flow and ecological environment damage. Since 1997, many rivers in Shenfu Coalfield Development Zone of Shaanxi Province have been cut off, such as 75d in 2000, 106d in 2006 and 1 in 2006. Due to cracks in the mined-out area of coal mine, the maximum width is more than 2 meters, and the ground in some areas drops by 2 ~ 3 meters. The Shuanggou River with the original flow of 7344 cubic meters/day has completely dried up, 26.67 hectares of paddy fields have become dry land, and poplar and other vegetation have died in a large area.
Collapse, Landslide and Debris Flow in 3.4.2.3
Mining residues excavated or accumulated on high and steep slopes of open-pit mines cause landslides due to heavy rain, ground subsidence and ground fissures. Landslides in coal mining areas mainly occur in open pit mines, loess plateau and mountain mines. For example, Sandaoling Open-pit Coal Mine in Hami, Xinjiang has suffered three large-scale landslides: 1967, 1983 and 1999, which caused traffic disruption in the mining area and direct economic losses of several million yuan. Due to the increase of coal mining, landslide activity in underground goaf of Shiguai mining area in Baotou, Inner Mongolia has intensified in recent years. At present, the landslide body is 100~370m ~ 370 m long from east to west, 600 m wide from north to south, with an area of about 16× 104m2 and a volume of about 400× 104m3. Since 1979, 5000m2 houses and other buildings have been destroyed, and the 600m road leading to Wudangzhao tourist attractions has been blocked, resulting in economic losses of about 4 million yuan. Many groups of ground fissures about 0. 1 ~ 1.5m in the east-west direction and about 100 ~ 300m in the north-south direction have appeared in Hongqi Mountain, endangering the lives and property of 677 households and 1947 people at the foot of the mountain.
Mountain creep caused by underground mining and canal seepage in Xiangshan Coal Mine, Hancheng, Shaanxi Province directly threatened the safety of Hancheng Power Plant, the main workshop of Kengkou Power Plant, and paid hundreds of millions of yuan for prevention and control. The strata above the mined-out area of Baizigou Coal Mine in Binxian County, Shaanxi Province collapsed, which made the surface slope out of balance, resulting in the loess landslide on July 6 1995, with a slip distance of about 30m, and the earthwork volume 180× 104m3 blocked the river and formed a dammed lake. The landslide pushed the three buildings in the mining department forward by 5 ~ 7 meters, resulting in cracks in the walls of the buildings, bulging floors and destroyed foundations. Fortunately, there were no casualties due to the accurate prediction in advance. 199 1 On August 9, 2008, the loess plateau on the west side of Jin Huashan coal mine in Tongchuan, Shaanxi Province was collapsed and landslide was caused by underground mining, and the earthwork volume reached 1050× 104m3, which buried Xilong village at the foot of the slope, destroyed a large area of fertile land and caused huge losses.
Serious landslides occurred in Jiaoping, Wangshiao, Lijiata, Jin Huashan, Taoyuan and other coal mines in Tongchuan, Shaanxi. There are more than 1,000 landslides 1 in Tongchuan mining area, 1 in Tongchuan urban area and 36 landslides1. Shenfu Dongsheng mining area is located in arid and semi-arid zone, with low vegetation coverage, staggered soil wind erosion and water erosion, loose rock structure, easy weathering, frequent natural disasters and very fragile ecological environment. Since 1980s, the coalfield has been mined in a large area, and the mined waste rocks and dumped soil have been piled up in disorder, and excavation along the hillside has increased the ground slope. Man-made debris flow in the mining area is distributed on both sides of the river, which directly flows into the river bed, reducing the cross section of the river bed and reducing the flood discharge capacity. Even if the water depth is moderate, it can cause great disasters. On July 2 1989 and July 2 1 day, there was a sudden rainstorm in the upper reaches of the mining area, with a rainfall of 3 hours 120mm, and debris flow with sediment concentration as high as 1360kg/m3 was formed in Wulanmulun River, with 1 1 sludge. Destroyed the mine embankment 1.870 m, irrigated land of 600 mu, subgrade retaining wall of 60 m, resulting in railway track interruption, traffic interruption for one month, and economic loss of more than 20 million yuan.
Land subsidence and ground fissures in 3.4.2.4.
Ground subsidence, ground fissures, farmland destruction, road collapse, rail distortion, building cracks caused by underground mining, and mine water seepage caused by underground water seepage along cracks. In arid areas, the destruction of surface water system makes it difficult to use water for production, life and agriculture in mining areas. At the same time, it can also induce mountain cracks to form landslides.
Land subsidence and ground fissures are the most common and serious disasters in large and medium-sized underground coal mining areas. Such as Liudaowan Coal Mine in Xinjiang, Huating, Yaojie, Agan Town and Wangjiashan Coal Mines in Gansu, Shizuishan and Shitanjing Coal Mines in Ningxia, and Weibeibei-Tongchuan and Shenfu-Dongsheng coalfields in Shaanxi.
According to the survey data, among 579 kinds of mines, there are 5 mines with ground subsidence1/kloc-0, covering an area of 20236km2. Among them, non-coal mines 10, accounting for only 8.70%; There are 0/05 coal mines/kloc-0, accounting for 9 1.30% of the collapsed mines. According to the subsidence area and severity, there are 8 mines with poor grade greater than 10km2, accounting for 8%. 1 ~ 1~ 10km2 has 37 mines with poor grade, accounting for 35%; There are 37 medium-grade ores with 0. 1 ~ 1km2, accounting for 35%; There are 23 ones with better grade less than 0. 1km2, accounting for 22%.
The ground collapse in coal mining area is the most serious, because the thickness of coal seam is more stable than that of metal ore body, the distribution range is wider, the occurrence of coal seam is more gentle, the goaf formed by coal mining is much larger than that of metal mine, and the overlying strata are mostly soft shale, siltstone and argillaceous rock. The range and depth of ground subsidence and ground fissures in coal mines are related to many factors, such as coal mining method, mining area of working face, recovery rate of mining area, coal seam occurrence and so on. Generally speaking, under the same conditions of other factors, the influence scope and depth of ground collapse caused by full mining (when fully mechanized caving is adopted in longwall working face) are greater than that caused by under mining (partial caving of strip). The greater the mining thickness of coal seam, the smaller the dip angle, the shallower the buried depth, the larger the mining area, and the greater the scope and depth of ground subsidence and cracks. The maximum surface subsidence w can be estimated by the formula: W=qMcosα.
Where q is the subsidence coefficient, q = 0.70 ~ 0.90 for full caving mining method, and q = 0.02 ~ 0.30m for strip partial caving mining method is the normal thickness of coal seam; α is the dip angle of coal seam.
When the ratio of mining depth to mining thickness is less than 20, the surface often undergoes severe deformation, and when the ratio reaches a certain level, the surface collapse disappears. 5 # coal seam is mined in Dalian Yao Coal Mine, Shenfu Mining Area, Yulin, with a thickness of 4 ~ 6m and a buried depth of 90 ~ 12000m2. 1On May 5, 1992, the ground collapsed at a depth of 0.7m above the mine. Relevant data show that the average ratio of the collapsed area to the mined area is 1.2, and the average ratio of the collapsed volume to the mined volume is 0.6 ~ 0.7. When the mining depth is large, there are fewer ground and surface cracks. When the mining depth h > (100 ~ 150) m, or F=H/M≥20(M is the thickness of coal seam), the surface movement and deformation are obviously continuous in time and space, and there is no ground fissure.
According to the Ninth Five-Year Plan of the coal industry, in 2000, the ground subsidence area of coal mines in China (except the northwest, the same below) was 182.20km2, the reclamation area was 48.40km2, and the reclamation rate was 26.6%. The ground subsidence area of coal mines in northwest China is 35.76km2, and the reclamation area is 4.40km2, and the reclamation rate is 12.3%, which is lower than the national average of 54.9% in the same period. In 2000, the coal output in northwest China reached 8994× 104t, and the subsidence area of ten thousand tons of coal was 0.3 1ha, which was 55% higher than the national average of 0.20ha, while the reclamation rate was 5 1.5% lower. It can be seen that the prevention and control of underground coal mining subsidence areas in northwest China should be stepped up.
Liudaowan Coal Mine in Urumqi is only 1.5km away from the friendly business center. The dip angle of coal seam in this mine is 67 ~ 78, which belongs to steep coal seam. In recent 50 years, due to the periodic collapse and fracture of the top coal and overlying strata, a strip-shaped collapse pit consistent with the strike of coal seam has appeared, with a depth of 40 ~ 50m, and parallel cracks have formed on both sides of the collapse pit, resulting in continuous ground. At present, the subsidence area is only used as a landfill of urban industrial waste in Urumqi, and new subsidence pits and ground cracks are constantly produced on the surface of its virtual soil. The land of 3km2 can't be developed and utilized, which forces the construction of municipal facilities to take a detour and becomes a dead corner of Urumqi's urban construction and development.
The mining area of Shizuishan Coal Mine in Shizuishan City, Ningxia is 5. 15km2, and the subsidence area has reached 6.97km2, accounting for 135% of its mining area, forming a surface subsidence depression with a depth of 8 ~ 20m, and the crack width in some sections is1m.. The railway transportation base in the mining area is higher than the subsidence area 10 ~ 20m, which makes the toll paid by mining enterprises for the railway as high as1000000 yuan every year, and the national road crossing the mining area 109 is forced to divert.
The total area of ground subsidence in coal mine goaf in Shaanxi Province is about 1 15km2 (Table 3-8), which is mainly distributed in Weibei and northern Shaanxi coal mining areas, with only sporadic distribution in Qinba Mountain area in southern Shaanxi. Among them, the old mining area in Tongchuan City suffered serious ground subsidence due to early mining. As of 1999, according to incomplete statistics, its ground subsidence is 63.82km2, accounting for 55.38% of the ground subsidence area in the coal mining area of the province, of which 80% is cultivated land. In recent years, the development of coal mines in Shenmu County has been increasing, and the area of ground subsidence has increased due to the shallow coal seam. By 200 1, the land subsidence caused by township coal mines in this county has reached 5.32km2
Table 3-8 Ground Collapse in Coal Mining Areas of Shaanxi Province
In the mining areas of Tongchuan, Huangling, Heyang, Baishui and Hancheng in Weibei coalfield of Shaanxi Province, and Daliuta, Dalian kiln, carambola, Shachuangou, Liuzhangou and Xinmin coalfield in Shenfu coalfield of northern Shaanxi Province, ground subsidence, ground fissures and landslides have occurred to varying degrees, resulting in large-scale farmland destruction, house cracking, railway track distortion and road collapse. The rainstorm in July, 2006, with an area of 5438+0.2km2, caused land subsidence and ground fissures in Cangcun Group 3 1.2km2 cultivated land in Shan Mei Coal Mining Area, Huanglingdiantou. The widest ground fissure is 15m, and the settlement gap reaches 7.45m. 60% of the cultivated land cannot be reclaimed, and the farmland is abandoned, with an estimated economic loss of 2.7 million yuan. In April 2000, CCTV's Focus Interview exposed the problems of villagers' cave cracking and cultivated land destruction caused by underground mining in Heichiyuan Township Coal Mine, Huangbao Town, Wangyi District, Tongchuan City, Shaanxi Province. Coal mining in Baishui County, Shaanxi Province led to cracks in the waiting room of Baishui Railway Station, rail sinking and ground uplift of the square. When the horizontal tensile deformation of the surface of Weibei coalfield in Shaanxi reaches 0.8 ~ 2.2 mm/m, ground fissures appear, with a width of 300 ~ 700 mm and a depth of 5 ~15 m. There are more than 5,400 ground fissures in Tongchuan mining area. Taking Wang Shi 'ao Coal Mine as an example, more than 70 fractures were drawn on the topographic map of 1:5000, with a total length of nearly 7000m. In 1990s, the mine floor in Yaojie coal mine area of Gansu Province covered an area of 598. 1ha, and there were 20 ground collapses, totaling 443.54ha. The ground collapse area was 48.4% larger than that in 1980s, and it expanded at the rate of 14.47ha per year. During the period of 10, many catastrophic geological accidents such as catastrophic landslides occurred. The area of soil erosion was 449～550 ha in 1980s and reached 663～720 ha in 1990s. In August, Wangjiashan Coal Mine, Jingyuan, Gansu 1995, two floods carried debris flows into the underground from ground cracks, causing many casualties.
A mined-out area was formed after 1997 in Daliuta coal mine area of Shenmu, Shaanxi Province, and ground subsidence and ground fissures appeared near 1998. The mined-out area of Daliuta mining area is about 3.9km2, with a total area of about 5.8km2 and a total area of ground fissures of about 5.45km2. The mined-out area of Huojitu well in Daliuta is too large, resulting in a large area of ground subsidence, in which the subsidence area of 205 working face is 0.3km wide and 3km long, with an area of 0.9km2, and a total of ground fissures 16 are found, which are distributed intermittently along the whole working face. The subsidence area of .. 206 working face is 0.3km wide, 3.5km long, with an area of 1.05km2. Five cracks with a width of 5 ~ 60 cm and a spacing of about 5 m were found .. The subsidence area of 207 working face is 0.3km wide, with a length of 1.5km and an area of 0.45km2, which is the whole subsidence. Among them, 5 fractures are well developed, with a width of 5 ~ 30cm and a spacing of about 10m. According to the measured data of Daliuta, Bulianta and Yujialiang mines in Shendong mining area, the ground subsidence area of ten thousand tons of coal is 0.35~0.42ha, which is almost 1 times of the ground subsidence area of ten thousand tons of coal in China. The main reason is that the coal seam is shallow (665,438+0 ~ 65,438+065,438+000 m) and thick (0,000 m).
Soil erosion in 3.4.2.5
According to the statistics of the Ministry of Water Resources 1992, the area of mild soil erosion in the western region is 104.07× 104km2, accounting for 58.05438+0% of the national soil erosion area. Soil erosion caused by soil erosion is an important factor of ecological environment deterioration. In the loess area and the transitional area between loess and desert, the possibility of soil erosion in mining area is the greatest. According to the environmental report data of Tongchuan, Hancheng and Shenfu coal mining areas in Shaanxi Province, the average erosion modulus of Shenfu-Inner Mongolia Dongsheng coal mining area is1.21×104t/km2 a, covering an area of 3024km2, and the annual water and soil loss is 3,659.04x1000. ; The average erosion modulus in Junggar mining area is calculated as1.30×104t/km2 a, the area is calculated as 1365km2, and the annual soil erosion is1774.5x104t. According to the remote sensing data of several mining areas in different periods before and after development, as well as the comprehensive analysis and calculation of river, dam and sediment data, it shows that the amount of soil erosion after coal mining is generally about twice that before mining. Before the construction of Huangling mining area in Shaanxi Province, soil erosion modulus was 500t/km2·a, and after five years of construction, soil erosion modulus reached1000t/km2 a. Soil erosion is very serious in Yaojie, Agan Town and Jingyuan coal mining areas in Gansu, Shizuishan and Shitanjing coal mining areas in Ningxia and Shenfu-Dongsheng coal mining areas in Shaanxi and Inner Mongolia. In Wuda and other coal mining areas in Inner Mongolia, the erosion modulus is10000 ~ 30000t/km2 a, which is 3.0 ~ 4.5 times of the water and soil loss before mining. This not only destroys the ecological environment, but also directly threatens the safety of the mining area. For example, in Zhongji Coal Mine, Shenmu, Shaanxi Province, slag poured into the river, occupying two-thirds of the riverbed, which blocked the river from flowing back in the rainy season in August of 1984, causing serious well flooding accidents.
Land Desertification in 3.4.2.6
The ground subsidence caused by coal mining destroys the balance of shallow groundwater system, and the vegetation in the subsidence area in some areas dies because of the decline of groundwater level, which forms or intensifies land desertification. Open-pit coal mines, transportation and natural gas pipeline projects occupy a large amount of cultivated land, destroy vegetation and activate some fixed and semi-fixed sand dunes. The accumulation and weathering of coal mine waste residue in Gobi desert area aggravated land desertification.
The large-scale development of Shenfu coalfield mining area in Shaanxi Province, as well as the indiscriminate excavation and mining by local and individuals along the banks of the river ditch, have destroyed vegetation, led to exposed sandstorms, and aggravated soil erosion and land desertification. Since the development in the mid-1980s, 666.7ha of cultivated land has been destroyed, more than 6000× 104t of waste residue has been piled up, and 4946.7ha of vegetation has been destroyed. The amount of sediment discharged into the Yellow River has increased to 20 19× 104t. According to the Environmental Impact Report of Shenfu Dongsheng Mining Area, if necessary sand control measures are not taken, when the production capacity of the mining area reaches 3000× 104t, the desertification area will increase by 129.64km2, the desertification area caused by coal mine development will be 1.53 times that caused by natural development, and the amount of sediment entering the river will increase by 480×.
Water and soil environmental pollution in 3.4.2.7
The pollution sources of coal mine water are mainly mine water, coal washing water and coal gangue leaching water discharged from coal mining. According to the related literature, the study on the geological environment of coal mines in the suburbs of Moscow shows that in the soil 50 ~ 60m away from the bottom of the gangue hill, the iron content in each 146 ~ 160mg soil reaches 160mg, and the aluminum content reaches1/kloc-0.
For a long time, due to the limitation of technical level and lack of understanding, mine water has been treated as a water hazard, and it has been discharged in vain without comprehensive utilization and protection. In 2000, the coal output of state-owned mines in northwest China was 3785× 104t, with an average drainage of10.3t, while the coal output of other mines was 5209× 104t, with an average drainage of 0.324t The coal mines in northwest China are mainly located in arid and semi-arid areas, and the mining areas are short of water resources. Uncontrolled drainage not only greatly destroys groundwater resources and increases the cost per ton of coal, but also leads to ground collapse, groundwater loss and water quality deterioration, and may also lead to sudden underground water seepage accidents.
Coal mine water is mostly acidic water, which is directly discharged without treatment, which aggravates the mine water crisis in arid areas. The pH value of some mine water in Shaanxi, Ningxia and Inner Mongolia is less than 6, and the pH value of Lijiata mine water in Tongchuan, Shaanxi is 3. The direct discharge of acidic mine water will destroy the living environment of aquatic organisms in rivers and inhibit the growth of vegetation in mining areas. Most of the mine water in Gansu, Ningxia, western Inner Mongolia, Xinjiang and central and eastern Shaanxi is high salinity water, and the salinity is generally greater than1000 mg/L. Among them, the salinity of most mine water in Jingyuan, Gansu is above 4000mg/L, especially in Wangjiashan Mine, which is as high as15000 mg/L.
In July, 2002, in the investigation of some mining bureaus in Weibei coal mining area of Shaanxi Province, it was found that some mines in Baishui County of Shaanxi Province directly discharged roadway wastewater into underground karst fractures, resulting in karst water pollution. This problem should be paid great attention to by relevant departments, and measures should be taken to protect karst water as soon as possible to prevent groundwater resources from being polluted.