| Coal and land are both important resources for human survival and development,While the development of coal resources play a significant role in the development of the national economy,it also inevitably causes severe disturbance and damage to the land ecology.The characteristics of China's energy resource endowments and economic and social development stages determine that the energy pattern with coal as the main energy status will not change in the long term.The westward shift of the coal development strategy and the favorable conditions of coal resources in the Shendong mining area have prompted the Shendong mining area to become the main battlefield for energy development at the current stage in China.The application of high-strength mining technologies such as the super large working face(SLWF)and cluster construction of large-scale coal bases make coal exploitation intensity of Shendong mining area continues to increase.However,the Shendong mining area has the inherent contradictory distinctive features of low ecological threshold,poor anti-disturbance capability,and large coal exploitation intensity.How to achieve safe,high-yield and high-efficiency mining of coal resources on the premise of protecting the ecological environment,while minimizing the damage to the ecological environment caused by coal mining,especially the minimization of land ecological damage,to achieve mining damage control and even active reduction of ecological damage due to coal mining,and to achieve the coordinated development of resource and environment for large-scale coal base in fragile-ecological mining areas,has become the research focus.Ecological environment damage in mining area,especially the land ecology damage,usually occurs in the mining process,the degree of damage to the rock and soil and the land ecology caused by coal mining depends not only on the ultimate state of the failure of the rock and soil,as well as the final outcome(static value)of the various indicators of mining subsidence,but also on the dynamic process of the movement and deformation of the rock and soil layers,and the evolution process of dynamic parameters(dynamic values)of mining subsidence.The in-depth study of the dynamic deformation process of the overlying rock and soil and the self-healing characteristics of the land damage during the mining process is the basis and prerequisite for a correct understanding of the impact mechanism of coal mining on the ecological environment in the mining area.Hence,it is necessary to carry out research on the dynamic deformation of rock and soil and the self-healing of land damage due to SLWF.This paper comprehensively uses the theoretical knowledge of surveying and mapping,mining science,mine pressure and rock formation control,land reclamation and ecological restoration,and studies the evolution characteristics of mining subsidence dynamic parameters and the dynamic distribution characteristics of mining ground cracks from the microscopic scale,then analyses the small-scale land damage characteristics due to mining ground cracks,an optimization monitoring strategy of land ecology damage based on the evolution characteristics of surface dynamic deformation parameters was proposed.A physical simulation experiment was conducted to explore the dynamic damage and self-healing characteristics of the overlying strata under the conditions of rapid mining of the super large working face,and to analyze the role of rock fracture angles and the overburden failure situation in the formation of subsidence basins.Based on the published studies,the mechanical rationality of multi-periodic development characteristics of dynamic ground cracks was elaborated,then to reveal the intrinsic formation mechanism of the multi-periodic development characteristics of dynamic ground cracks.And from the perspective of systematic research,the self-healing characteristics of rock and soil damage and ecological damage,and their internal correlations were studied from the macro and micro scales,respectively.The intrinsic mining driving mechanism of mining subsidence basin self-healing characteristics was revaled based on the dynamic evolution characteristics of faliure situation of overburden due to SLWF,from the co-evolutionary view of rock stress and strain due to mining.Then the targeted land reclamation and ecological restoration methods and strategies were proposed based on the self-healing characteristics of land ecology damage.The main conclusions obtained are as follows:(1)The evolution characteristics of dynamic parameters of mining subsidence due to SLWF in windy and sandy region and its impact on land ecology were revealed.(1)Mining subsidence dynamic parameters play an important role in the deterination of the extent and scope of land ecology damage during mining.The dynamic curves of fore-effect distance/angle,dynamic curves of maximum subsidence rate,dynamic curves of lag distance of maximum subsidence rate are consistent with the change of exponential function,the dynamic parameter change curve has an inflection point when the mining distance is 1.2 H,and reached a steady state and tending to constant,serious land ecology damage occurred in the stage of rapid change of dynamic parameters,an optimized monitoring strategy of land ecology damage was proposed based on the evolution characteristics of dynamic subsidence parameters,the key monitoring area and the in-situ and dynamic monitoring strip should be laid out,and the corresponding monitoring areas are recommended.(2)The formation process of mining ground cracks due to SLWF was analyzed,mining cracks were classified into various categories and the factors influencing the formation of ground cracks were analyzed.By monitoring the cracking process of the dynamic ground cracks in the horizontal direction and the comparison of the marginal crack gap with the corresponding subsidence value,the small-scale damage characteristics of the mining cracks to the land are quantitatively analyzed.(2)The dynamic movement deformation process and self-healing characteristics of the rock and soil mass due to SLWF are studied:(1)Under the conditions of rapid mining of SLWF,the broken rock block of the roof has a certain degree of skewness due to the hysteresis of the dynamic stress of the roof rock.The fracture angle on the side of open-off cut is larger than that of the working face,resulting in a certain degree of skewness in the failure situation of the rock and soil layer,and the underlying cause is the different mechanical mechanism of the overlying rock fracture on the side of the open-off cut and the side of working face.(2)Under the conditions of rapid mining of SLWF,the rock fracture angle is relatively large and the goaf reaches the super-critical state,more broken rock blocks are pressed backwards and pressed against the goaf and accumulated,and the broken rock blocks at the bottom of the goaf are compressed,as the degree of extrusion continues to increase,more mining stress is transferred to the goaf,while the mining rock around the goaf is subject to relatively lower mining stress,the redistribution and relbancing of mining stress due to SLWF,and the lithology of the overburden and its combination are mutual coupling bodies,and both have the characteristic of stress-strain co-evolution.(3)Under the conditions of rapid mining of SLWF,the overburden rock fractured rapidly and violently at the initial mining stage,however,as the advance distance increases,the excavations will be completed under the conditions of less deformation of the rock and soil overlying the goaf,and the time of movement and deformation of the rock and soil will be relatively reduced,and continuous tight rock fractures will develop on the roof and its overlying strata,and the geotechnical structure will be intact,resulting in the increasement of the uniform subsidence area and the time reduction of movement and deformation of the overburden,the damage degree of rock and soil was reduced,and the ?self-healing? of rock and soil layer damage under the conditions of rapid mining of SLWF was realized.(4)Under the conditions of rapid mining of SLWF,the space for initial collapse of fractured rock mass is relatively large.The fractured and failure blocks can be discharged relative freely in the goaf.The stratigraphic features of the rock layers weakened,and the orderly arrangement of the rock masses in the goaf gradually increased from the bottom up.(5)Under the conditions of rapid mining of SLWF,the fracture and collapse of overburden have important influences on dynamic movement deformation characteristics such as surface dynamic subsidence curve,horizontal deformation,curvature deformation,etc.,especially for subsidence,horizontal deformation,and curvature deformation.The dynamic surface displacement value has a jumping characteristic,which indicates that there is a region where the surface is repeatedly subjected to tensile and compressive deformation.When the deformation value exceeds the limit of the surface soil strength,multiple cracking and closure of the surface soil will be triggered.(6)The maximum subsidence value of each monitiored rock layer is highly linearly related to the distance from the bottom plate in the process of rapid advancing,indicating that the migration process of each rock stratum has high overall coordination and is conducive to compaction and closure of strata cracks between rocks.The subsidence value of each rock stratum has certain regional characteristics in the coal rock columns around the open-off cut and working face,the subsidence value of the subterranean rock layer is relatively large,while the subsidence value of the rock layer closer to the coal seam floor is relatively small.(3)The self-healing characteristics of the damaged overburden and its intrinsic mining driving mechanism are analyzed systematically,while the formation mechanism of the multi-period development characteristics of dynamic ground cracks is revealed.(1)Based on published research,the distribution of rock fractures in the overburden have obvious regional characteristics via experimental simulations,the rock fractures on the side of the working face have a larger range and extent than the fractures on the side of the open-off cut.The rock fractures above the falling rock band have a rapid closing ?self-healing? feature and a large range of self-healing areas.The self-healing characteristics of mining subsidence basins due to SLWF are summarized and analyzed taking the parameters of fracture angle,moving angle,offset point of inflection,and main tangent value as indices.(2)Starting from the leaping characteristics of surface subsidence velocity change caused by rock fracture,the mechanical rationality of the ?M?-type dual-cycle development feature of dynamic mining cracks is analyzed.Based on the correlation between the dynamic changes of surface subsidence velocity and the fracture of rock layers,especially the key stratum,it is considered that the dynamic mining cracks not only have the "M" type of dual-cycle development characteristics,but also show the characteristics of multi-period development under certain conditions.The multi-period development characteristics of mining cracks are essentially caused by the differences in the direction of rotation and the amplitude of rotation of broken rock blocks.(3)Based on material mechanics and elastic mechanics knowledge combined with rock formation control theory,the development characteristics of rock fracture angles under conditions of rapid mining due to SLWF were analyzed,then the internal mechanism for the self-healing characteristics of subsidence basins are analyzed based on the development characteristics of rock fracture angles,while the intrinsic mining driving mechanism of the self-healing characteristics of mining subsidence basins is revealed from the perspective of co-evolution of stress and strain in mining stress and strain fields.According to the field observations,the natural repair process of mining cracks and soil crusts was analyzed.(4)According to the self-healing characteristics of the rock damage,subsidence basins,and land ecology damage due to SLWF,the differential rapid restoration model and concurrent mining and reclamation method are proposed. |
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