Microstructure And Failure Mechanism Analysis Of Rockfill Concrete Interface In Guizho

Rock-fill concrete(RFC)is a new concrete dam construction technology.Compared with the traditional concrete dam construction technology,it has the advantages of low construction cost,short construction period and environmental protection,so it has been widely used in hydraulic engineering.Most of the studies regard RFCS as three-phase composite materials composed of rockfill,self-compacting concrete(SCC)and the interface between them at the microscopic level.At present,the research on various properties of rock and SCC have been relatively mature,but there are few studies on related properties and failure mechanism of the rock-SCC interface.In addition,at present,Guizhou is the region that uses the most rockfill concrete technology.Therefore,this paper carries out a series of experimental studies on the interface of RFC in Guizhou,explores the failure mechanism and micro-morphology of the interface of RFCS,analyzes the influence of related factors,and provides a theoretical basis for the engineering application of RFC in Guizhou and the whole country.The main research contents of this paper are as follows:(1)Using raw materials,SCC mix ratio and curing conditions from an actual reservoir project A in Guizhou,12 RFC standard cube composite specimens with three interface types,namely smooth,natural and chiseled hair,were prepared.Splitting tensile test and compressive strength test were used to study the bond strength of RFC interface.The results show that the bonding strength of the rock-SCC interface increases with the increase of the rock surface roughness,and the influence of the interface roughness on the bonding tensile strength is greater than that of the bonding compressive strength.At the same time,the transverse and longitudinal strains at the rock-SCC interface were measured by the strain gauge,and the strain law of the RFC interface during the failure process and the bonding mechanism between rock and SCC were obtained.(2)Taking the surface roughness and normal load as variables,the shear mechanical properties of the RFC interface were tested on the RFC composite specimen with smooth,natural and chiseled interfaces under different normal loads.The results showed that the shear strength of the interface increased with the increase of the surface roughness of the rock under the same normal load.According to the failure form of the specimen and the load displacement curve of the shear process,the influencing factors of the interface shear strength were obtained,and the shear mechanism of the RFC interface was analyzed according to the test results.(3)Using the RFC test chamber prepared in a practical project B in Guizhou according to the same raw materials,construction technology and curing conditions as the dam body,the test chamber was cut and the cubic specimens with side lengths of150 mm,300mm and 450 mm were tested for tensile strength and compressive strength,and the test results were compared and analyzed with the bond strength of the RFC interface.The influence law of bond strength of RFC interface on the whole RFC was explored.The experimental results show that the bond splitting strength and bonding compressive strength of RFC interface are far less than that of the whole RFC,and the bonding strength of the interface determines the upper limit of the splitting strength and compressive strength of RFC to a certain extent.The interface is the weakest part of RFC,and the compressive strength of the interface is better than that of the tensile strength.(4)Electron microscope scanning and energy spectrum analysis tests were conducted on the interface of RFC composite specimens made in the laboratory and RCF specimens before and after failure in actual engineering B,to explore the microscopic changes of the interface before and after failure,and to obtain the failure mechanism of the RFC interface.The experimental results show that the microstructure of engineering RFC at the interface is more dense than that of laboratory composite RFC.After RFC failure,the pores in the interface transition zone increase and SCC detaches from the rock surface,which corresponds to the separation of rock and SCC on the macro level.The content of Ca,O and C elements is the highest in the transition zone of the interface region,and a large number of Ca(OH)2 crystals are generated in the transition zone of the interface region,which is one of the reasons for the weakness of the RFC interface.(5)A two-dimensional RFC composite specimen model was established by finite element software to study the bonding and shear properties of the RFC interface.The interface element was selected as conhesive element with no thickness,and the nonlinear analysis was carried out by means of displacement loading.The simulation results under different test conditions were basically consistent with the test results.It provides a reliable finite element analysis method for the interface simulation of RFC.