| Huainan is the main coal base in China;large amount of abandoned lands,abandoned mines and other abandoned remnants emerged after the closure of mines.Potential hidden dangers such as environmental safety and human settlements would be inevitable once land reclamation and ecological reconstruction are not well conducted.The resource-exhausted mining area of Datong coal mine,with an area of about 5.7 square kilometers,is the central area connecting the old and new urban areas.Considering the importance of the geographical location and urgency of development of the study area,research on ecological restoration technology at the exhausted area of Datong coal mine in Huainan plays an important role in enhancing regional economic structure and promoting sustainable development.Meanwhile,it is of extremely significance for the management and development of resource exhausted mines in other resource-based cities.The Datong coal mine resource exhausted mining areas was selected as the research object.Both field sampling and laboratory test were applied in this study.Both the ground transient electromagnetic test and the network parallel electrical technology were carried out to evaluate the geological stability of the subsidence area.In addition,the scientific problems such as the repair technology of damaged river system,the technology of ecological restoration and the construction technology of constructed wetland were studied.The main conclusions were listed as follow:(1)There were few natural water bodies in the study area.Most of the water bodies were formed by collapse pits,with the water quality of V and even inferior V.The pollution was mainly TN,TP,COD and heavy metal.The elevated pollution level in the Datong wetland might be attributed to the chemical waste and coal gangue leachate.(2)The soil nutrients in the study area were evaluated synthetically by Z-score standardization,principal component analysis and cluster synthesis method.The results showed that the F value of soil nutrients in the study area was-5.64-1.06,and the soil nutrient status ranged from lack level to extreme lack level.Heavy metal pollution level in the soil was from moderate pollution to heavy pollution with Cd and Cr heavily polluted.The ecosystem of artificial restoration in Datong resource exhausted mining area is simple and not stabilized yet,and the plantation had obvious high values of heavy metal(3)The physical and mechanical properties of loose layers were determined by borehole sampling and indoor geotechnical test,transient electromagnetic method and network parallel electrical method.As was shown,due to the repeat excavation of the small coal mines,the middle and eastern part of the goaf area were of relative activation;thus those two parts were regarded as the unstable region,other areas were supposed to be stable regions without the influence of repeated mining of small coal mines.(4)According to the comprehensive analysis of the basic process of wetland water cycle,hydrogeological conditions and natural water cycle factors,the response relationship among wetland surface area,water storage volume and wetland inflow volume were analyzed.Meanwhile,the relationship between wetland surface area and wetland discharge volume were figured out to investigate the water balance equation of closed wetland in Datong coal mining subsidence area and construct the water cycle model of Datong wetland.(5)Many ecological restoration technologies,including the terrain reconstruction technology,the gangue matrix profile reconstruction technology,pollution control technology,pond anti-seepage technology,species selection and optimization technology of plant community were studied in this study to improve the eco-environment of the coal mining subsidence area.The vegetation cover,the water quality and the.ecological landscape in the exhausted mining area of Datong are expected to improve once the aforementioned methods applied.(6)In order to control the soil erosion of the soil slope and improve the landscape conditions,the slope surface restoration technology of the three dimensional vegetation net on the soil slope was studied.This technology can not only successfully construct artificial shrub herbaceous plant communities of Lespedeza,IPM and Bermuda on soil slope of quarry,but also can effectively control soil erosion of soil slope surface.The advantages of this technology includes both replacing the non-woven cover by shade cover of three dimensional vegetation network technology and overcoming the deficiencies in the use of non-woven fabrics.In addition,this technology can not only be used in the quarry slope formed by the building,but also in other types of the slope less than 30 degrees.Moreover,this technology can be applied to the soil which contains stone,brick construction waste and coal gangue.(7)A set of technology was designed for the treatment of chemical waste leachate.This technology was consisted of both coagulating sedimentation and subsurface flow wetland.First,the technology of coagulation sedimentation was used to pretreat the leachate,and then the artificial wetland purification system was introduced for further treatment.The average removal rates of total nitrogen,ammonia nitrogen,total phosphorus and permanganate index were 60%,72.75%,38.75%,and 20%,respectively.Furthermore,toxicity tests showed that the improved inhibition effect of leachate on ryegrass growth and the increased cultured chlorella were found. |
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