Study On Strength Damage And Creep Characteristics Of Cemented Gangue Backfill In Mine Water Environment

The use of cemented gangue backfill material for structural backfill mining can effectively solve the resource and environmental problems faced by coal mining and realize resource reuse,which is of great significance to reduce carbon emissions and realize“peak carbon dioxide emissions”and“carbon neutrality”.Due to the complex underground environment,there is often a large amount of mine water.Mine water generally contains erosive ions such as SO₄^2-,H⁺,Mg²⁺,Cl^-and HCO₃^-.The backfill body in it not only needs to bear the load of overlying strata,but also is subjected to long-term chemical erosion of erosive ions.The strength and deformation will change,and in serious cases,instability and failure will occur,thereby affecting the stability of roof.Therefore,it is of great significance to study the strength damage and deformation characteristics of gangue cemented backfill body（CGBB）under the coupling effect of load and mine water erosion to ensure the long-term stability of backfill for maintaining the stability of goaf.In view of this,this paper systematically studies the strength damage and creep characteristics of CGBB in mine water environment by experimental research and theoretical analysis.The main research contents and conclusions are as follows:（1）The strength changes of CGBB with age in different environments（air,water,H₂SO₄solution,coupling H₂SO₄ solution and load）were carried out.It was found that the compressive strength of CGBB cured in air and water increased with the increase of age,and the growth trend gradually slowed down.The strength of CGBB in H₂SO₄ solution increased continuously in the first 90 days and the growth rate was greater than that of CGBB cured in air and water.After reaching the maximum value at 90 days,the strength decreased continuously and the decline rate gradually accelerated.The strength of CGBB under the coupling effect of H₂SO₄solution and load decreased slowly with age due to the compaction effect of load.The long-term stability of CGBB can be monitored by resistivity and ultrasonic.（2）The long-term strength and creep test of CGBB under different p H value of H₂SO₄solution,different stress strength ratio and different erosion modes were carried out.The results showed that the deformation of CGBB under different compressive stress in H₂SO₄ solution increased with time,and the early growth was faster,and the later growth was slower.The larger the p H value of H₂SO₄ solution,the faster the deformation of the CGBB in the early stage,and the slower the deformation in the later stage.The creep of the CGBB with side immersion erosion was much larger than that with top erosion.The creep model of CGBB in H₂SO₄solution was established.Combined with SEM and XRD,the loading with 80%stress strength ratio caused irreparable damage to the CGBB,which accelerated the penetration of erosive ions in the CGBB.The sudden change of acoustic emission（AE）energy can be used as a precursor to determine the failure of CGBB.（3）The long-term strength and creep tests of CGBB with different grades of stress in Mg SO₄ solution were carried out.It was found that in the range of less than 50%stresss trength ratio,with the increase of compressive stress,the compressive strength of uneroded specimens and eroded specimens gradually increased,and the increasing trend was gradually flat.The deformation of eroded and uneroded CGBB increased with time and compressive stress level.The initial growth rate of the deformation of the backfill without erosion was relatively fast,and the later growth rate was relatively slow,and finally tended to a constant value.The initial deformation of the eroded CGBB was similar to that of the uneroded CGBB,but it still increased greatly in the later period.（4）The strength and deformation size effect tests of CGBB in H₂SO₄ solution were carried out.The results showed that the uniaxial compressive strength of CGBB decreased with the increase of size under different conditions,and the effect of loading on the resistance of the CGBB to H₂SO₄ attack was greater with the smaller size.The sudden change of the AE ringing and the stable stage of the resistivity could be used as the precursor to determine the failure of CGBB.The whole field strain evolution cloud map observed by DIC technology can show the whole process of the initiation,propagation,connection and penetration of the surface crack of the specimen.According to the peak stress,peak strain,Weibull fractal parameters,elastic modulus and other parameters of different sizes of CGBB,the damage model and constitutive equation of CGBB under standard curing for 28 days and the coupling effect of H₂SO₄ solution and load were obtained,which provided theoretical guidance and data reference for the design of backfill body in structural backfill.