Reserch On Development Mechanism And Spatiotemporal Evolution Of Shallow Mining Ground Fissures In Shendong Mining Area

Shendong mining area has the geological characteristics of shallow burial depth,thin bedrock,thick coal seam and thick loose layer.Large mining height and rapid advance mining methods are often used in this area,resulting in a large range of damage to the overlying strata,fully developed fissures,or the overlying bedrock strata cutting and breaking through the surface,forming obvious collapse pits and ground fissures,resulting in damage to the original fragile ecological environment.Therefore,guided by the concept of green mining,this paper studies the generation mechanism and spatial evolution law of shallow mining ground fissures in Shendong mining area.By comprehensively adopting the research methods of field investigation and monitoring,laboratory test,theoretical analysis and numerical simulation,the formation mechanism of mining ground fissures in the shallow buried coal seam in Shendong mining area was analyzed,and the geometric model of the mining surface and overlying rock space failure of the shallow coal seam in Shendong mining area is constructed,which provides a scientific basis for the implementation of comprehensive post-mining control.The main results are as follows:(1)The structural characteristics of the overlying strata in the mining area are analyzed,the failure characteristics of the rock mass after the overlying strata migration and instability during the mining process are studied,and the deformation and failure process of the rock mass at the mining face is revealed.The total strain energy occupied under the condition of high loading rate is higher than that under the condition of low loading rate,and the crack opening is larger.The microscopic failure mechanisms of uniaxially compressed rocks under different loading rates are mainly tensile and shear mixed failures.Between the rates of 0.06 and 0.3 mm/min,the microscopic failure mechanism of the rock is mainly shear crack development,and between 0.5 and 5 mm/min,the microscopic failure mechanism of rock is dominated by the development of tension cracks.Brazil splits the rock with different loading rates,the loading rate is between 0.03 and 0.5 mm/min,the microscopic mechanism of rock crack failure,and the shear crack is positively correlated with the loading rate.When the loading rate is between 1 and 3 mm/min,the microscopic mechanism of rock microscopic failure is mainly tension crack.(2)During the mining process,the overlying strata fracture developed and formed after the overlying strata migrated and became unstable,and the cracks penetrated and induced the formation of ground fissures with different damage forms on the ground:the formation stage of overlying strata fracture,the expansion stage of overlying strata fracture,and the stable expansion stage of overlying strata fracture.The fracture area of overlying strata is divided into 6 zone: layer separation fracture area,layer separation compaction zone,caving fracture zone,vertical fracture zone I,vertical fracture zone II,separation layer fracture zone,and layer separation fracture zone II produces a step-like fracture pattern,among which the vertical fracture the expansion angle of the cracks in zone I and zone II is 0～90°,basically developed vertically,the cracks are superimposed and broken,and the cracks are vertically penetrated.Type I expansion and development of overlying strata fracture(fracture opening type 3),fracture closure(shear type 2 to 4 zone),and type II expansion and development of fissures are inhibited.Near the working face,the overlying strata fracture developed I-II mixed type(fracture tension-shear type 1 and 2 zone),and numerical simulations were carried out to simulate the advance distance and different mining heights affecting the development height of fissures at the same time.A quantitative description of the relationship between mining height and advancing distance is fitted.(3)In order to predict the development and evolution of the overlying strata fracture zone in Shendong mining area,the sample parameters of the mining area under the conditions of shallow burial mining in the Shendong mining area and some surrounding mining areas were collected,and the factors affecting the height of the water conducting fractured zone were selected quantitatively,there are six influencing factors: length of the working face,mining height,mining depth,coal seam dip angle,advancing speed,and hard rock proportional coefficient.Based on the GA-BP neural network topology,construct a GA-BP neural network for predicting the height of the water conducting fracture zone,the model has accuracy and general practicability for highly nonlinear prediction of water conducting fracture zone in Shendong mining area.(4)According to the morphological characteristics of the shallow mining overburden fractured fractures in Shendong mining area after the deformation and damage of the ground surface,through simplifying the two dimensional and three dimensional geometric features,the two dimensional plane model and the three dimensional spatial distribution geometric model of the fully broken fracture of the overlying stratum are obtained,and the range of the fracture and ground deformation and damage of the overlying rock after full mining is obtained.Then,the evolution space form of overlying rock fissures and surface damage was analyzed by numerical simulation calculation,and the damage degree was defined to quantitatively describe the spatial damage degree of the fissures.And the variation law of overlying rock and surface subsidence displacement is calculated,and finally the spatial morphological characteristics of overlying rock and surface damage are analyzed.(5)The joint detection of underground fissures by UAV infrared system and ground penetrating radar is constructed.Through the practical application of this method in the typical working face of Shendong mine,the evolution process of ground fissures and the temperature field distribution characteristics of hidden ground fissures during the advancing process of the entire working face are obtained,and the different temperature distributions and measured data in each area of the ground are analyzed.The area with temperature higher than the threshold in the infrared image is divided into hidden ground fissures and verified by ground penetrating radar detection.The monitoring method was implemented in the mining area,and the monitoring data information of ground fissure in different time periods was obtained.It is analyzed that different recovery and treatment measures can be taken for different mining ground damage situations.Ultimately,it provides a scientific basis for the research on the fine identification and restoration of fissure in the Shendong mining area,and realizes the sustainable development of the green mining ecological environment.