Study On The Stability Of Horizontal Pillar Mining Under Tailings Filling Body

There will be problems with residual mineral resources to varying degrees in underground mining of metal mines.In particular,various pillars left by two-step multi-stage mining,and residual ore after mining rich and discarding poor,etc.According to preliminary statistics,only residual minerals in nonferrous metal mines account for 30%to 35%of the existing resource reserves.It is important to fully recover various residual pillars while ensuring safety.The horizontal pillar between stages is a typical type of residual pillar.This paper takes a copper mine in Jiangxi Province as the research background.Using various research methods such as theoretical analysis,numerical simulation,and similar simulation.Firstly,the safe mining height of the horizontal pillar is obtained by the calculation and analysis of the mechanical model of the horizontal pillar under the tailings filling body.Secondly,the variation rules of stress field,displacement field and plastic zone caused by pillar mining under dynamic and static loads are analyzed.The deformation characteristics and acoustic emission evolution characteristics of horizontal pillar mining under different mining heights were analyzed through similarity simulation tests.The main research contents and conclusions are as follows:（1）Calculating the overlying load of horizontal pillars using Janssen’s theory of dispersion.Based on the occurrence environment and stress conditions of horizontal ore pillars,a mechanical model of rectangular equal thickness thin plates for horizontal ore pillars was established.It is calculated that the ultimate mining height of the horizontal pillar is 8m,and the remaining 5m is not mined by the tensile limit equilibrium theory in material mechanics,（2）Simulated horizontal pillar mining under static and dynamic loads using FLAC^3D.After 8 m of horizontal pillar mining,shear failure occurred locally in the connection area between the horizontal pillar and the inter pillar.But the remaining 5 m of horizontal pillar did not show plastic zone penetration.The maximum principal stress value of the remaining horizontal pillar is 2.19MPa under static load.The maximum subsidence displacement is2.7cm.The maximum principal stress value will decrease by about 0.1MPa,and the displacement settlement value will increase by a maximum of 0.6cm under dynamic load.Resulting in an increase in the range of plastic zones.（3）It is obtained that the maximum displacement of pillar subsidence before the collapse of horizontal pillar reaches 0.97 mm by the similar simulation test of horizontal pillar mining.After the collapse of the horizontal ore pillar,it is divided into two parts,and the tailings filling body overlying the horizontal ore pillar falls in an"arch shape".With the increase of mining height of horizontal pillars,the evolution scale of internal cracks in horizontal pillars gradually increases,and tensile cracks are the main type.（4）It is found that with the increase of mining height of horizontal pillar,the acoustic emission event rate and energy significantly increase,and the instability and damage of horizontal pillar instantly reach the maximum value.The main frequency and sub main frequency of acoustic emission are distributed in strips,with a trend of"increasing first and then decreasing"in quantity.Near the horizontal pillar,the main frequency and sub main frequency high-frequency signals disappear due to instability and destruction.The acoustic emission dominant frequency ratio is distributed in the range of 0 to 6,and the overall average dominant frequency ratio exhibits a"sudden drop,steady rise"variation rule.The highest frequency band energy of acoustic emission signals gradually shifts from 0 to 62.5k Hz to 62.5to 125k Hz by analyzing the characteristics of acoustic emission signals during horizontal pillar mining.（5）The time series relationship between the acoustic emission signal parameters such as Ib value,S value,AF,RA,and the instability and failure point of horizontal pillars during mining is analyzed,and an evaluation system for the instability and failure of horizontal pillars based on multiple acoustic emission signal parameters is established;The BP neural network is used to effectively identify the precursor information of acoustic emission instability failure of horizontal pillars,with a recognition accuracy of 95%.