Study On The Performance Evolution Of The Gangue Cemented Backfill Material In Salt Corrosive Environment

The backfill body formed during the backfill mining is subjected to not only the compressive stress from the overlying rock formation,but also the chemical crossion from the harmful ion in the mine water,which results in the deterioration of backfill material performance and leads to a decrease in the bearing capacity of the backfill body and even a loss of stability.It will cause low backfill efficiency.In this paper,based on laboratory test and theoretical analysis,the evolution and mechanism of the backfill’s strength and relative dynamic elastic modulus,the creep characteristics of the backfill material and the diffusion law of the sulfate ion in the backfill material were simulated.Detailed research conclusions are as follows:（1）The axial compressive strength and relative dynamic elastic modulus of backfill materials in different corrosive media with the age of corrosive change show a decreasing trend after the first addition,and the greater the concentration,the faster the rate of increase or decrease.Adding a small amount of magnesium salt helps improve the early sulfate resistance of the backfill material,while magnesium salt and bicarbonate salt will reduce the long-term sulfate resistance of the backfill material,and the bicarbonate corrosion resistance deteriorationofganguecementedbackfillmaterialismoreobvious.The sulfate-magnesium-bicarbonate composite solution has the highest erosion performance.（2）The XRD and SEM show that the swelling effect of the corrosion products ettringite and gypsum on the backfill material causes the internal expansion and cracking and even spalling;the corrosion products of M-H-S and thaumasite without cementation continuously make the surface of the specimen softened and peeled off,eventually losing the strength and destroying.（3）The modified creep prediction model calculation formula was used to analyze and discuss the axial compression mean creep of salt-corrosive the gangue cemented backfill material.The results show:Under salt corrosion,the creep deformation of the gangue cemented backfill material is divided into two stages,rapid deformation stage within 0-60 days and slowly increasing stage over 60 days;Under the effect of salt corrosion,the axial deformation of the gangue cemented backfill material is greater than that of single salt corrosion or loading.The higher the holding load,the longer the corrosion time and the greater the creep;The average creep value with 40%stress level increased by 15.74%compared with 30%,and the average creep value with 50%stress level increased by 23.20%compared with 40%,when loading erosion 0¹800d;The influence order of ion concentration on the average creep value of filling body erosion is:three-fold composite>SO₄^2-and HCO₃^-double compound>SO₄^2-and Mg²⁺double compound>single SO₄^2-.（4）The diffusion coefficient of sulfate ion is a function of time.With the increase of time,the diffusion coefficient of sulfate ion decreases exponentially.Increasing Mg²⁺and HCO₃^-in the external erosion solution will accelerate the long-term diffusion coefficient of sulfate ion in the backfill material,and HCO₃^-will have even more influence on the transmission of sulfate ion in the backfill material.For the same infiltration time,the greater concentration of Mg²⁺and HCO₃^-,the greater content of sulfate ion at the same depth of the backfill material,and the corresponding larger diffusion coefficient;With the increase of the compressive stress level,the content of sulfate ion in the backfill material increases,and the diffusion coefficient increases.