Research On Mutual Feedback Mechanism Of The Web Pillar And Slope Stability In Highwall Mining Of The Lignite Open-pit Mine

In China,the open-pit coal mining are extremely important.To ensure slope stability,a reasonable stripping ratio,and the limitation of the mining boundary,a large amount of residual coal can not be recovered under the highwall.The development of highwall mining technology provides a new method for the recovery of residual coal.Highwall mining does not need stripping or infrastructure again,which main form is to excavate the exposed residual coal seam by remote control of the highwall miner,and the web pillars are set between the chambers.The parameter design of the web pillar has an important impact on its own and the slope stability,and which is the prerequisite for safe and efficient application of highwall mining.At the same time,the slope parameters also affect the stability of the web pillars,therefore,the mutual feedback mechanism of the two should be clarified,and the parameters of the two should be collaboratively optimized.At present,the research on the mechanism,width design of the web pillar and slope stability calculation under the highwall mining condition is relatively fewer,which has some limit on the development of highwall mining technology.In order to solve the problem of cooperative stability of pillar and slope in highwall mining,this paper takes the west highwall of Huolinhe north open-pit coal mine as the engineering geological background,the concept of target time strength is put forward considering the creep characteristics and service time requirements of the lignite pillar.The variety pattern of shear strength with time is analyzed.The software FLAC3D is applied to numerically simulate the bearing stress distribution in pillar under the condition of the slope "triangle loading",the interaction with critical strength,and the distribution characteristics of plastic zone.The instability mechanism of web pillar is revealed.The reserved width of coal pillar is designed.Through the test of similar material simulation,the instability evolution law of web pillar is analyzed and the rationality of the design of coal pillar width under the condition of ultimate mining depth is verified.Combined with the numerical simulation and test results,the bearing mathematical model of web pillar is established.Based on the catastrophe theory,the cusp catastrophe model is constructed.The instability criterion of coal pillar is deduced,and the design method of coal pillar parameters is put forward.Based on the discontinuous structure surface theory,the failure mode of slope and the change rule of the evolution weak-layer mechanics parameters under the condition of highwall mining are analyzed.The appropriate stability calculation method is proposed.The interaction between the web pillar and slope stability under the condition of highwall mining is studied and quantified.The width of the pillar and the shape of the slope are optimized.The results show that the shear mechanical index of coal pillar decreases exponentially with the increase of time for a certain period in shallow buried coal seam.There is "end effect" in the highwall mining,the peak bearing stress appears in front of the engineering position of maximum mining depth,which is independent of the width of coal pillar,and the tendency distribution of bearing stress is similar to "bowl type",The ultimate strength of coal pillar increases with the increase of width.When the load of coal pillar exceeds its bearing capacity,the progressive shear instability failure will occur.The precondition for sudden instability of web pillar is that the width of yield zone(2xp)on both sides is more than 0.88 of the total width of coal pillar(ws).For the highwall mining,the potential sliding mode changes into a cutting-bedding sliding mode with evolution weak layer as the bottom interface.The width of yield zone of coal pillar is affected more by load than the strength of target time.With the increase of mining depth,the width of yield zone increases gradually,and the mechanical parameters of evolution weak layer decrease gradually.Cooperatively considering the stability of web pillar and slope,the reserved width of web pillar of ws=5.9m and the slope angle of ?=38° is determined.There are 124 figures,37 tables and 125 references in this paper.