Experimental Study On Mechanical Properties Of Cemented Backfill Considering Layered Characteristics Under The Influence Of Multiple Factors

With the mining enterprises at home and abroad digging deep underground,the application of mine filling technology is increasing.To achieve better underground filling effect,scholars at home and abroad further study and optimize the mine filling technology.Due to some subjective and objective limitations of mining enterprises and filling slurry,it is inevitable that different layered structures will appear in the filling body,and the influence of layered structures on the filling effect can not be underestimated.Therefore,it is of certain practical significance to carry out experimental research on the mechanical characteristics of layered cemented filling and analyze the influence of layered characteristics on mine filling work.After a battery of laboratory experiments,combined with theoretical and numerical simulation analysis,the effects of proportion of cement to tailings and mass concentration on rheological properties of tailings filling mud was studied,and the variation law of strength and failure mode of cemented filling body considering layered characteristics at different curing ages and loading rates was explored.The creep characteristics of intact cemented filling body and layered cemented filling body were compared and analyzed,and a suitable creep model was established.The main research contents and conclusions are as follows :(1)The tailings and cement of an iron mine in Jiangsu Province and a gold mine in Shandong Province were tested and analyzed,and uniaxial compression tests were carried out on different cemented fillings.It was determined that the raw materials of cemented fillings were tailings of an iron mine in Jiangsu Province,P·O42.5 ordinary portland cement and laboratory tap water.(2)Rheological tests of tailings filling slurry with cement-sand ratios of 1:4,1:6,1:8,1:10 and mass concentrations of 72%,74%,76% and 78% were carried out respectively.Rheological properties of cemented filling slurry were studied,and the curves of shear stress-shear rate and viscosity-shear rate are obtained,and the changing rules between them are analyzed respectively,and the plastic fluid Papanastasiou model was selected and used to study and predict the change of shear stress and viscosity of filling slurry with shear rate.(3)The orthogonal test was carried out with the middle layer cement-sand ratio,curing age and loading rate as the factor variables.It is concluded that the curing age had a significant effect on the uniaxial compressive strength of the simple,while the loading rate had no significant effect on the uniaxial compressive strength of the filling body,the reason is that when the loading rate increases gradually,the strength of layered cemented backfill rises first and then goes down.(4)Uniaxial compression tests with loading rates of 0.2 mm/min,0.5 mm/min,1.0mm/min,1.5 mm/min,2.0 mm/min were carried out for layered cemented fillings with slurry mass concentration of 72%,upper and lower layer cement-sand ratio of 1:4 and middle layer cement-sand ratio of 1:6,the curing ages are 3,7 and 28 days.The change law and failure mode of mechanical properties of layered cemented backfill under the influence of various factors are discussed,and the strength regression equation was established for layered structure of cemented fillings.(5)Uniaxial creep tests were carried out on the complete cemented backfill with72% slurry mass concentration and 1:4,1:6,1:8 and 1:10 cement-sand ratio,and the three layered cemented backfill with 72% slurry mass concentration,1:4 cement-sand ratio of upper and lower layers and 1:6 cement-sand ratio of middle layer,and found an improved Poyting-Thomson creep model,the mechanical characteristics and deformation behavior of cemented backfill are studied,and the influence of layered interface on its long-term strength is analyzed.(6)Based on the data results of uniaxial compression test of complete cemented backfill and layered cemented backfill,parameters such as elastic modulus and Poisson's ratio were obtained.The strain softening model of cemented backfill specimens is established by FLAC 3D,and the uniaxial strength numerical simulation of complete cemented backfill and layered cemented backfill is carried out respectively.The results are fit perfectly with the results of laboratory test,which proves the reliability of laboratory test and the correctness of analysis and conclusion.