Study On The Method Of Determining The Equivalent Density Of Mechanical Tests For Different Grades Of Rockfill Materials

There are many high earth-rock dams built and under construction in China.As the main filling material of dams,the mechanics of rockfill materials has always been the main concern of dam construction circles.Because of the limitation of the size of indoor instruments,it is necessary to scale the rockfill materials in the experimental study.Whether there exists such a scale theory to ensure that the mechanical properties of rockfill materials are basically the same before and after scale reduction,that is to say,it is still a question worth discussing that the mechanical properties of original graded materials can be reflected by the results of material test after scale reduction.It is impossible that the mechanical properties of rockfill materials before and after scale reduction are identical,and it will be the research goal to reach the acceptable level of geotechnical engineering.The problem is further simplified.How to determine the laboratory test density of the reduced sample(homologous material,different gradation)and its mechanics reflects the mechanical characteristics of the field rockfill material is always a key technical problem in soil mechanics.Previous studies mostly used relative density method to determine the density of rockfill laboratory test.The deformation experience of rockfill dam shows that there is still a big gap between the mechanical index of rockfill provided by laboratory test and the reality.Taking the scale theory of rockfill as the research objective,large-scale model tests and large-scale triaxial tests are systematically carried out in laboratory.The determination methods of equivalent density of different graded rockfill materials under the same modulus of lateral pressure are discussed.The following conclusions are drawn:(1)When the gradation and stress state of the rockfill are constant,the modulus of the rockfill body is very sensitive to the change of density,and the modulus of the rockfill body increases with the increase of density,showing a non-linear positive correlation.(2)The mechanical properties of rockfill materials with the same material,particle shape and stress state and different gradation and density are the same when the modulus of side pressure is equal.It is expected that the equivalent density under the condition of equal scale gradation and side pressure modulus will be used as the mechanical index to reflect the mechanical characteristics of the original graded rockfill.(3)There are some uncertainties in the results of triaxial test of rockfill materials,that is,the results of triaxial test of rockfill materials with the same gradation,density and stress state are also different.Parallel tests can reduce the uncertainty of rockfill test results.(4)Duncan-Chang model has some deviation in fitting the stress-strain curve of rockfill,especially it can not reflect the dilatancy characteristics of rockfill.The K-KG model proposed by Changjiang River Scientific Research Institute is obviously superior to Duncan-Chang model.In a word,reasonable scale theory,rigorous test and scientific constitutive model are the basic guarantee for correctly simulating the stress and deformation of high earthrock dam.