Strength And Acoustic Characteristics Of Layered Cemented Tailing Backfill

The backfill mining method is the most popular mining method at home and abroad.In the production practice,to improve the economic benefit,different concentrations or discontinuous filling slurries will be used in the same goaf,resulting in the backfilling body apparent stratification phenomenon.The stability of layered backfill seriously affects the safety of mine production.Therefore,it is of great engineering significance to monitor and early warning of the deformation and failure of backfill by using the characteristics of ultrasonic and acoustic emission signals.In this paper,the backfill body with different layered factors was taken as the research object,the acoustic emission and ultrasonic experiments were carried out in the process of uniaxial loading,and the influence of different delamination factors on the mechanical properties of the backfilling body was analyzed.During the process,the acoustic emission parameters and main frequency changes of the backfilling specimens under different layering factors,the ultrasonic coda wave interferometry was used to analyze the variation rate of coda wave velocity during uniaxial loading.The main conclusions are as follows:(1)The failure process of layered backfill specimen is very similar to that of rock material,which has experienced four stages: compaction stage,linear elastic stage,microcrack evolution stage,and failure stage.The uniaxial compressive strength of the backfill specimens decreases with the increase of the number of layers.The extension of the backfill interval will reduce the uniaxial compressive strength of the test pieces.The relationship between the uniaxial compressive strength and the number of layers can be expressed in the form of a power function.The relationship between the uniaxial compressive strength and the backfilling interval can be expressed in a logarithmic function.(2)Due to the influence of delamination surface,the AE event rate and ringing count rate of the specimens with two and three delaminations increase gradually during uniaxial compression,and there is no apparent sudden increase point.With the increase of delamination numbers,the order of cumulative ringing count decreases.And the longer the backfilling interval,the lower the stress and the energy ratio.The higher the number of delamination,the higher the RA value is in the early stage of loading when the ratio of lime sand is 1:4 and 1:8,which means that the earlier the time of tensile crack is.(3)With the increase of delamination times,the minimum correlation dimension D value of ringing count is gradually increasing,the degree of order is decreasing;and the later the minimum value of D appears,the more time the disordered state takes up,and the more cracks will appear in the failure process.The longer the backfilling interval,the smaller the minimum correlation dimension of the ringing count.At the initial stage of loading,the dominant frequency of all kinds of layered backfill specimens is mainly in the frequency band of 30 k Hz ? 60 k Hz and 120 k Hz ? 130 k Hz.When loading to the peak stress,most of the layered specimens are dense,and the dominant frequency of 260 k Hz ? 320 k Hz appears.(4)The increase of the coda velocity change rate indicates that the coda velocity increases,and the specimen's pores are compressed tightly.The decrease of coda velocity change rate indicates that the specimen has a new crack,which affects the wave propagation.With the increase of the number of layers,the loading force required for the wave velocity varying rate's minimum value is smaller.The more the number of layers is,the faster the wave velocity vary rate decreases.From the point of view of the sudden drop of the minimum coda velocity variation rate,the longer the backfilling interval,the more significant the sudden drop of coda velocity variation rate.This phenomenon shows that the longer the backfilling interval is,the greater the influence on the wave velocity is.