Study On Mechanical Properties Of Backfill With Early Strength Agent Under Different Loading Rates

With the concept of green and safety deeply rooted in the hearts of the people,the filling mining method has been gradually popularized and applied in mines.Filling body is an important bearing unit in the mine,whether as a support or a pile cap.While it meets its own stability and realizes the balance of adaptive stress of surrounding rock,it puts forward higher requirements for the early strength.Therefore,early strength agent is often added to the filling slurry to improve the strength of the filling body.When the filling body is in the action stage,the loading rate produced by the working face advancing also has a significant impact on the mechanical properties of the filling body.In order to explore the mechanical properties of backfill mixed with early strength agent under different loading rates,based on the uniaxial compression acoustic emission test,combined with classical mechanics,the mechanical characteristics and damage evolution law of backfill under the combined action of early strength agent and loading rate were analyzed.The main research contents and results are as follows:(1)Uniaxial compression tests were carried out under different loading rates.It was found that under the condition of a certain loading rate,the strength and elastic modulus of the specimen increased first and then decreased with the increase of the content,and there was a critical content at different loading rates.For example,the critical content under the loading rate of 0.1 mm/min,0.5 mm/min,and 0.7 mm/min is2.0 %;when the dosage is certain,the loading rate also has a critical value.For example,when the dosage is 0.0 %,1.0 %,3.0 %,the critical loading rate is 0.3mm/min,and when the dosage is 2.0 %,the critical loading rate is 0.5 mm/min.(2)The failure of the specimens with early strength agent under different loading rates is mainly tensile failure,but at low loading rate of 0.1 mm / min,the failure is mainly tensile-shear composite failure.When the loading rate increases to 0.3 mm /min and above,the specimen is mainly tensile failure.Compared with the specimens with 0.0 % and 3.0 % content,the specimens with 1.0 % and 2.0 % content were less damaged at the same loading rate.(3)When the specimen is pressurized under different loading rates,the peak values of the ringing count rate and energy rate of the specimen often appear in the failure stage under the action of low loading rate.Under the action of high loading rate,the peak value of acoustic emission signal in the specimen basically appears in the initial stage of loading,and the acoustic emission activity is more active at this time.(4)Through the analysis of RA-AF three-dimensional scatter diagram and the proportion of shear signal,it can be seen that the RA signal fluctuates in the range of0 ～ 5 ms/V,the AF signal is distributed in the range of 0 ～ 1000 k Hz,and the RA signal distribution is synchronized with the shear signal proportion fluctuation.The change trend of the proportion of shear microfractures shows a trend of decreasing first and then increasing.Before the failure stage,the proportion of shear microfracture signals begins to rise,indicating that the sample is about to lose stability.(5)Combined with the ringing count rate,energy rate and RA-AF analysis,it can be seen that when the ib value drops sharply or is in a low state,the ringing count rate and energy rate of the specimen reach the peak state,which reflects the sudden occurrence or large-scale rupture in the specimen.The change trend of ib value is opposite to the general change trend of shear signal proportion in RA-AF analysis,which reflects that the increase of shear microcracks promotes the penetration of internal cracks.