Study On Stability Of North Slope Of Fushun West Open-pit Mine Under Underground Mining Conditions

When mining under the slope of open-pit mine,the stress and deformation of slope rock and soil will become more complex under the influence of underground mining,and its stability will also be greatly affected.Taking the north slope of Fushun West Open-pit Mine as the research object,this paper studies the deformation law and failure mechanism of open-pit slope under underground mining conditions,the treatment of goaf and the stability evaluation of open-pit slope by means of field investigation,theoretical analysis,numerical simulation,apply strength reduction method and limit equilibrium method calculating the safety factor of stability and hierarchical fuzzy comprehensive evaluation.The main research results are as follows:(1)Based on the analysis of the survey and design data of the west open-pit mining area in the past,and on the basis of mastering and sorting out the topography,geological structure,stratum structure and hydrogeological conditions of the study area,the general factors affecting the slope stability of the open-pit mine are put forward,and the influence of underground mining on the slope stability is emphatically analyzed.The conclusions are drawn as follows:(1)Underground mining reduces the strength of rock and soil mass of the slope;(2)Underground mining breaks the balance state of the original stress in the slope;(3)Underground mining changes the hydrogeologycal conditions of the slope.(2)Based on the detailed study of the geological conditions in the study area and the theoretical analysis,the failure mode of the northern slope of the west open-pit mine under the influence of underground mining is determined.According to the failure mode,the deformation and failure area is divided into slip failure area,dumping deformation area and subsidence deformation area.(3)Using numerical simulation to analyze the deformation of open pit slope under the condition of underground coal seam mining,it is concluded that under the condition of underground mining,the deformation of rock and soil mass of the north slope of West Open pit Mine changes from the simple slip to the combination of subsidence and slip during open pit excavation to the movement mode of subsidence and slip,and the displacement of the slope increases significantly compared with that of single open pit mining.With the enlargement of mining scale,the displacement is increasing nonlinearly.(4)The deformation of open-pit slope under underground coal seam mining is analyzed by numerical simulation.It is concluded that under underground mining conditions,open-pit slope mainly shows the deformation characteristics of underground mining,and according to its deformation characteristics,the slope is divided into tension deformation area,mining subsidence area and swelling deformation area.(5)According to the results of comprehensive numerical simulation,stability coefficient calculation and hierarchical fuzzy comprehensive evaluation,the northern slope of West Open-pit Mine is in a stable state when underground mining is not carried out;after underground mining,its stability will be greatly reduced,and with the expansion of mining scale,the northern slope of West Open-pit Mine will cause severe damage to the goaf.When backfilling mining is used,the slope of open pit mine tends to displace in the slope as a whole,but backfilling mining can effectively control the displacement and deformation of the slope,making the overall stability of the slope better,and the local steps of the slope of open pit mine may be destroyed.At the same time,due to the overall displacement of the slope,the rock and soil mass on the upper wall of the top fault F1 will produce subduction settlement along its fault fracture zone,and the deformation in the area between the top fault F1 and F1 A will further increase.