Analysis And Evaluation Of Surface Deformation Damage And Failure In Multi-face Mining In Loess Gully Region

The Loess covered area in the west is the main coal producing area in China.The complex terrain factors of the Loess mining area have a significant influence on the mining subsidence characteristics.The interval pillars of working face under the condition of fully mechanized caving in multi working face also have important influence on the surface subsidence characteristics,which leads to the complex mining subsidence law in Loess mining area.For a long time,due to the lack of the support of the observation data of the surface moving observation station,the academic research on the above problems is not enough.In this paper,Wenjiapo coal mine and Dafosi coal mine in the typical binchang mining area were selected as the research area.By using the measured data of surface movement,combined with theoretical analysis,numerical simulation and geotechnical test,the quantitative analysis and evaluation were carried out for the surface deformation and failure characteristics of the multi working face mining in loess gully area.The main contents and results are as follows:(1)The main characteristics of surface deformation and failure under the mining conditions of multiple working faces were analyzed by the measured data.Based on the monitoring data of Wenjiapo and Dafosi Coal Mines,the dynamic subsidence characteristics and three-dimensional moving track of the surface points were analyzed.The spatial and temporal characteristics of the moving deformation of the surface points above the coal pillars and goaf were obtained.The results show that under the condition of multi working face mining,the surface movement process is violent and the damage range is enlarged;the deformation characteristics of the surface movement on the inclined line are obviously asymmetric,and the current surface subsidence curve of the working face mining tends to the side of the old goaf.In view of the mining surface cracks after mining in shallow coal seam,a method of measuring surface fractures based on aerial photos of low altitude UAV was proposed,and the formation mechanism and development characteristics of mining fractures were analyzed.(2)The distribution characteristics of sliding deformation of mining slope and volume deformation of mining soil unit in loess gully area were revealed by computer numerical simulation.The numerical simulation results show that the surface movement deformation is influenced by slope slip and mining subsidence deformation.The slope slip and the volume deformation of soil element are not only related to slope shape and slope,but also to the relative position of goaf and slope;the volume deformation of soil unit in near surface mining is equal to the sum of horizontal deformation and vertical deformation,and the value is dominated by horizontal deformation,and There are different distribution characteristics above the coal pillar and goaf.The deformation characteristics of the surface movement are different under different mining depth conditions.(3)Based on the measured data of surface movement,the prediction model of surface subsidence under multi working face mining conditions was improved,and the stability change of slope under the influence of mining in loess gully area was quantitatively evaluated.Based on the existing probability integration model,the piecewise prediction function of surface subsidence was constructed,and the asymmetry characteristics of surface subsidence in old goaf and coal pillar side were better fitted under the condition of multi working face mining.Based on the field sampling geotechnical test,the physical and mechanical parameters of soil with different compactness were determined.The functional relationship between the deformation of soil element and the physical and mechanical parameters of soil mass was established.The safety coefficient of mining slope was calculated according to the limit balance method of soil slope stability.The quantitative relationship between slope gradient change and slope safety coefficient under multi working face mining was obtained.It can provide reference for quantitative evaluation of mining damage in western loess mining area.