Experimental Study On Creep And Acoustic Emission Characteristics Of Backfill Under Three-point Bending

In the downward filling mining method,the cemented filling body is the main core bearing unit,and its stability is very important for the safe and stable operation of the mine.It is of great practical significance to study its fracture characteristics.Three-point bending test is one of the common methods to study the fracture characteristics of filling body.During the service period of the filling body,its instability failure is not instantaneous,but the continuous loading leads to the superposition of internal damage and eventually leads to the creep failure of the filling body.Based on this,a three-point bending creep test system suitable for filling body was designed in this paper.The flexural strength of filling body with cement-sand ratio of 1:4,1:6 and 1:8 was measured by three-point bending test.On this basis,seven-stage three-point bending creep acoustic emission test was carried out on the above filling body,and each stage was loaded for 8h.The three-point bending creep characteristics and acoustic emission characteristics of tailings cemented filling body under different cement-sand ratios and different load levels were studied.The main conclusions are as follows :(1)The macroscopic fracture failure characteristics of the cemented tailings backfill with three different cement-sand ratios all show a through crack in the middle,which is wide in the lower part and narrow in the upper part.The tailings cemented backfill body has significant creep characteristics under three-point bending.The whole process of creep instability failure is manifested in three creep stages :deceleration,steady state and acceleration.The backfill body with cement-sand ratio of 1:4 and 1:6 enters the accelerated creep stage at the 7th load level,and the backfill body with cement-sand ratio of 1:8 enters the accelerated creep stage at the 5th load level.(2)The instantaneous creep amount,final creep amount,final creep rate and load level of tailings cemented backfill with three different cement-sand ratios all show a quadratic function growth relationship.However,with the increase of cement-sand ratio,the instantaneous creep amount,final creep amount and final creep rate all show a downward trend.(3)For the filling body with different cement-sand ratio,the cumulative number of acoustic emission events,cumulative ringing count and cumulative energy during the creep failure process have a good correspondence with the change law of three-point bending creep curve.The specific performance is that the acoustic emission event rate,ringing count rate and energy rate decrease in the deceleration creep stage.In the constant creep stage,the acoustic emission event rate,ringing count rate and energy rate remained stable.In the accelerated creep stage,the acoustic emission event rate,ring count rate and energy rate have the characteristics of sudden increase.(4)When the load level of the filling body with cement-sand ratio of 1:4 and 1:6is 16% ～ 64%,and the load level of the filling body with cement-sand ratio of 1:8 is16% ～32%,the acoustic emission b value is at a high level in the deceleration creep stage,and enters a fluctuating downward trend in the steady-state creep stage;when the load level of the filling body with a cement-sand ratio of 1:4 and 1:6 is 80% ～86%,and the load level of the filling body with a cement-sand ratio of 1:8 is 46% ～80%,there is no overall upward or downward trend,but the fluctuation range is large;When entering the last load,the acoustic emission b value is at a high level in the deceleration creep stage and the steady-state creep stage,but it remains relatively stable overall,and there is a transition decline in the accelerated creep stage.(5)Both Burgers model and Findley power law model can well characterize the three-point bending creep curve of cemented tailings backfill,but Burgers model has higher goodness of fit.For Burgers model,the fitting parameters a,b,c and d increase with the increase of load level,and the parameters a and d are linear,and the parameters b and c are quadratic.