Discussion on the Influence of Juye Coalfield Development on Geological Environment

(Shandong Lunan Geological Engineering Survey Institute, Yanzhou 272 100)

About the author: Bu Hua (1967—), male, senior engineer, engaged in hydrogeology, engineering geology, environmental geology and geological disaster exploration.

Abstract: Juye coalfield is the largest undeveloped high-quality coalfield in Shandong and even East China, and has entered the stage of comprehensive and substantial development. This coal field has a large area, large reserves and high degree of development, which has seriously damaged the geological environment. According to the occurrence characteristics and development planning engineering characteristics of this coalfield, this paper makes a preliminary analysis and discussion on its influence on geological environment.

Key words: Juye coalfield; Geological environment; surface collapse

Juye coalfield is the last large-scale comprehensive coalfield with proven reserves in Shandong and even East China, and has now entered the stage of comprehensive and substantial development. The development of this coalfield is of great significance to improve the self-sufficiency rate of coal in Shandong and East China, promote further economic development, especially to maintain the sustainable development of Shandong's coal industry and promote the economy of western Shandong. However, the development of coal resources is often at the expense of geological environment, which has caused serious impact or damage. Juye coalfield has a wide coal-bearing area, thick coal seam and centralized synchronous mining, and its development will definitely have a serious impact or permanent change on the geological environment in this area.

1 Overview of Juye Coalfield

Juye coalfield is located in Heze City and Jining City in the southwest of Shandong Province, and it is distributed in a north-south direction. Coal-bearing area 12 10km2, and coal geological reserves are 55.7 1× 108 t. After deducting temporary unrecoverable reserves, the planned geological reserves at this stage are 30.96x100t, and the coal-bearing strata are Taiyuan Formation and Yuemengou Formation of Carboniferous-Permian. Coal-bearing 6- 100t, in which No.3 coal seam (Shanxi Formation) is the main coal seam, with an average thickness of 5.96m in the north and 7.58m in the south, with a maximum thickness of 1 1.36m, a buried depth of 500 ~ 1200m and a maximum buried depth of/kloc. The main coal seam has a large thickness, good coal quality, stable distribution, coal seam dip angle of 2 ~ 19, moderate structural degree and good mining conditions. The whole coal field is divided into seven mine fields, with a total construction scale of 1860× 104t/a and a service life of 50 ~ 77 years, as shown in table 1.

Table 1 List of Basic Information of Various Minefields in Juye Coalfield

2 regional geological environment background

Juye coalfield is located in the western part of Huang-Huai-Hai Plain, with a flat terrain and a ground elevation of 37 ~ 46.2 m. The micro-geomorphology types include gentle slope, shallow depression, basin depression and floodplain highland. There are many rivers in this area, and the utilization of surface water is high. Irrigation from the Yellow River is the main form of farmland water use in this area, and the level of groundwater exploitation is low. This area is a famous production base of high-quality grain, cotton and oil in China, and its economy is dominated by agricultural cultivation, with a weak industrial base.

Geographically, the coal field is located in the northwest of the fault block depression in southwestern Shandong, and the fault structure is relatively developed, which controls the distribution boundary of the coal field. The strata are mainly Ordovician, Carboniferous, Permian, Neogene and Quaternary. The Neogene and Quaternary loose sediments are 450 ~ 800 m thick, and the main lithology is silty clay, clay, silty soil and silty fine sand.

The lithology of vadose zone is mainly silty soil, and the soil environment quality is good under the current conditions, and it is basically unpolluted. Loose sediment is the main occurrence medium of groundwater in this area, and its water abundance is seriously restricted by topography, burial conditions and sedimentary environment, with great spatial differences. The shallow and ancient river belts are rich in water, and the unit water inflow is 200 ~ 400 m3/(d m); The deep water area and the river-crossing area have poor water yield, and the unit water inflow is less than 200m3/(d m). The main sources of groundwater are atmospheric precipitation infiltration and river water leakage, which flows from west to east and is mainly discharged by lateral runoff and evaporation. The buried depth of the average water level for many years is 2 ~ 5m, and the hydrochemical types are complex and changeable, with high background content of chemical components and poor water quality, mostly salt water or brackish water.

Since the neotectonic movement, the crust in this area has shown the characteristics of overall subsidence movement, and the fault activity tends to ease and the crust is relatively stable. Soil salinization has been effectively controlled and the degree of harm has been basically eliminated; Influenced by modern sedimentary environment and groundwater level, the main environmental geological problem at present is sand liquefaction.

3. Influence of coalfield development on geological environment

3. Impact of1on topography, landform and stratum structure

Juye coalfield is a fully concealed mine field. The roof is managed by vertical shaft development, single longwall mining, retreating mining and full caving, which has a serious impact on the overlying strata structure, topography and geomorphology, and the main manifestation of the impact is ground collapse. According to the occurrence characteristics of coal seam and the designed mining area of coal field, the theoretical subsidence value 10mm is taken as the cut-off point affected by mining, and the probability integral model is selected for preliminary prediction. Under the condition of fully mining No.3 coal seam in the design mining area, the ground subsidence area will reach nearly 570km2. Due to the concentration of mines, the mining areas are basically connected, and the subsidence area will become a regional artificial basin. Under the condition of current water level depth, the water accumulation area is about 180km2, which is equivalent to 1.8 times of the normal water area of Dongping Lake. The average depth of the subsidence area is about 4.7m, and the maximum depth will reach 9m.

After the development of coal field, the geological environment in this area will change seriously. On the surface, the terrain elevation will be lowered, the broad and flat plain will become a great basin, the part where the subsidence depth exceeds the groundwater level will become a stagnant lake, and the edge of the subsidence basin will form an inclined "slope", resulting in a complex shape of rugged, and various original landforms will no longer exist. Underground and overlying strata collapse, and its original structural characteristics such as stress state, integrity and continuity are destroyed, especially the shallow modern sedimentary structure becomes more loose.

3.2 Impact on groundwater environment

There are two main impacts on groundwater environment: first, coal mining leads to ground subsidence, which destroys the original structure of aquifer, breaks the natural circulation conditions, dynamic characteristics and equilibrium state of groundwater, turns groundwater into surface water, and the original runoff, evaporation and mining emissions become direct evaporation emissions on the water surface, which is accelerated by mine drainage, thus reducing regional groundwater resources; Assuming that the surface evaporation, surface runoff and underground seepage are not considered, the water resources equation in this area is that the consumption is equal to the surface evaporation minus the precipitation. The annual average precipitation in this area is 696.9mm, the annual average evaporation is191.9mm, and the evaporation gap is 12 15mm. Second, groundwater pollution caused by mine drainage, mining production, domestic drainage and coal gangue leaching; After all the seven mine fields are completed and put into operation, the total displacement of the mine is about (6.9 ~ 7.7) × 104m3/d, the external displacement after deducting the reuse amount will be greater than 5.6× 104m3/d, and the displacement of production and living is about (0.9 ~1) ×/kloc-0. Mine water is grayish black, containing a large number of suspended impurities, a certain number of microorganisms and some heavy metal elements. Domestic sewage contains more bacteria and organic matter. In addition, the content, salinity and total hardness of mine water in this area are also high, especially the coal preparation wastewater contains toxic additives such as flotation oil and flocculant (Shan, 1999). If the water is discharged into rivers or collapse pits through open channels, it will not only pollute the surface water, but also seep into the groundwater and pollute it. A large number of coal gangue produced by coal mining will be leached and washed by rain, and the dissolved pollution components will penetrate into the ground with water, which will also pollute the groundwater environment.

3.3 Impact on soil environment

Land subsidence destroyed the structure of soil, and a large area of land accumulated water turned into lakes, and the spatial environment, internal structure and exchange conditions of soil changed, which reduced or lost the production capacity and the function of purifying the environment. Then, the construction of mining area and the accumulation of coal gangue occupied a large area of farmland, and the land lost its original use function. Harmful substances in mining areas, coal gangue and discharged wastewater seep into soil with water, which increases harmful components or content and deteriorates environmental quality.

3.4 secondary geological disasters

Coal gangue is an inevitable product in coal production, which usually accounts for 10% ~ 20% of coal output (Chen et al., 1999). The discharge rate of coal gangue in Juye coalfield is close to this value, which is about 10.4% ~ 19.7%. If the median is 65438+.

In the gentle slope area of subsidence area, due to the decrease of surface elevation, the groundwater level rises relatively and the evaporation increases. With the increase of water level, the salt accumulated on the surface increases, resulting in secondary salinization of land. According to preliminary calculation, the area of secondary salinized land is about 100km2.

In the process of mine construction and mining, with the excavation of foundation pit, site leveling and other engineering activities and ground subsidence, the surface vegetation and soil structure are destroyed, the soil becomes loose, and the terrain slope increases, which leads to the decrease of soil cohesion and internal friction, the enhancement of erodibility, the decrease of erosion resistance and the intensification of soil erosion.

4 Conclusions and suggestions

Juye coalfield is located at the junction of Shandong, Jiangsu, Henan and Anhui provinces, with superior geographical position and convenient transportation. Its development is of great significance for alleviating the contradiction of energy demand in East China and promoting the sustainable development of regional economy. At present, the land in this area is vast, agriculture is developed, the geological environment is basically in a natural state, and the influence of external dynamic geological processes is relatively weak. Coalfield development will cause environmental geological problems such as land subsidence, water pollution and secondary geological disasters, among which land subsidence has the greatest impact on the geological environment, which will permanently change the topography of this area, turn the vast plain into a large area of artificial subsidence basins and stagnant lakes, change and reduce the land use function, and make the geological environment more fragile.

Geological environment is the foundation of human existence. In the process of coal field development, we should strictly follow the principle of regional mineral development, effectively handle the relationship between resource development, society and environment, pay attention to the implementation of various pollution prevention measures and comprehensive ecological environment improvement plans, and do a good job in environmental protection while developing.

refer to

Chen, Yang Xinrong,. 1999. Talking about the environmental problems and countermeasures of coal mines in China. See: Editor of the Editorial Board of Coal Mine Environmental Protection. Excellent paper on coal mine environmental protection (1). Beijing: Coal Industry Press, 82.

Shan Zhong Jian. 1999. Some environmental problems in coal production and processing and coal washing measures. See: Editorial Committee of Coal Mine Environmental Protection. Excellent paper on coal mine environmental protection (1). Beijing: Coal Industry Press, 58.