Research On Overburden Rock And Surface Movement And Deformation Under Repeated Mining

With the continuous development of human society and the increasing consumption of resources,mankind is facing the challenge of lack of resources,especially coal resources have been particularly prominent in recent years,shallow coal resources have gradually dried up,and human beings are continuing to deepen mining will result in repeated mining.Repeated mining of multiple layers of coal will cause instability of the stress balance in the regional rock mass,causing geological disasters such as ground collapse,ground fissures,collapse,and landslides.Shanxi is located on the east bank of the middle reaches of the Yellow River,on the Loess Plateau in the western part of the North China Plain.The province has many mountains and few rivers and complex landforms.Shanxi is a major coal mining province in China,the coal seams in the region are diverse,the recoverable coal seams in this study area are 8^#coal and 11^#coal,the interval between coal seams is about 45 m,the thickness of 8^#coal is between 2.71 m and 7.1 m,the average mining depth is about 130m,and the thickness of 11^#coal is between 1.97 m and 8.81 m.The average mining depth is about 160 m,and the surface of the study area is largely covered by Quaternary Loess and Tertiary Baode Laterite,and the surface is undulating.Most of the 8^#coal seam in the study area has been mined,and it is expected to mine 11^#coal seam.Based on on-site investigation and data collection,this paper calculated the height of the water conduction fracture zone,the depth of the floor failure zone,the surface movement deformation value and the deformation duration through theoretical calculations,and simulated the research area through the finite difference numerical simulation software FLAC^3DThe internal 8^#coal mining process and the 11^#coal downward mining process are compared.Comparing the calculation results of the two,it is found that most of the theoretically calculated movement deformation values are greater than the numerical simulation results,and the maximum surface subsidence value is located in the goaf on the slope body directly above the center,the surface subsidence range under the undulating terrain is a near ellipse with the mined-out area as the center,and the overburden failure height,surface subsidence value and influence range further increase under repeated mining are based on the initial mining,due to the hard cover rock in the study area,the amount of cover rock and surface deformation is small.Simplified the three-dimensional numerical model of the study area,and studied and analyzed the characteristics of overburden and surface movement and deformation caused by repeated mining with the four variable factors of repeated mining method,coal seam mining sequence,interval between coal layers,and surface form.(1)The maximum surface subsidence value caused by longitudinal repeated mining is greater than that under horizontal repeated mining,and the influence range under repeated mining has obvious directionality.The direction of working face advancement is the main increasing direction of the surface subsidence basin;(2)The maximum subsidence value on the ground under downward mining is greater than that in upward mining,and the maximum value of overburden tensile stress is greater than that under upward mining;(3)Repeated mining under different coal intervals,with the increase of coal interval,the maximum subsidence value of the surface gradually decreases,and the maximum tensile stress of overburden rock is consistent with its changing characteristics;(4)With repeated mining in the mountainous terrain,the surface is subsidence value at the beam and grotto site increased compared with the horizontal terrain,and the upward uplift value at the gully area increased,and the horizontal stress formed a stress concentration zone in the valley,causing the topsoil layer to slip.The above research results have certain reference value for the safe mining of the repeated mining face under the geological conditions and similar geological conditions,the prediction of ground subsidence and the reduction of mining damage.