Research On Mechanical Properties And Impermeability Of Rockfill Concrete In A Real Projec

Rock-filled concrete（RFC）is a new type of concrete formed by filling rock voids with self-compacting concrete（SCC）with good fluidity.Compared with conventional concrete,the particle size of rock aggregate is larger,generally between300-1000 mm.The traditional mechanical performance test method is difficult to apply in RFC,which makes it difficult to obtain the basic mechanical performance index of RFC.In addition,there are few studies on the impermeability of RFC,which limits its popularization to a certain extent.In this paper,based on the RFC test bins A and B（Their sizes are 5 m×7 m×2.2 m and 2.2 m×2.2 m×2.2 m）that were poured in the field 14 years apart and were consistent with the two actual projects（the same material,the same process,and the same maintenance environment）,the test bins were cut into relevant test size specimens and transported to the Civil Engineering Experimental Center of Guizhou University for testing.Based on the collected practical engineering data of multiple RFC,the main contents and conclusions of this paper are as follows:（1）The RFC test bins A and B were cut into RFC specimens with different sizes（side lengths of 150mm,270mm,300mm,450mm）.The cube compressive test,splitting tensile test and elastic modulus test were carried out respectively.The results show that:1.The compressive strength and elastic modulus of RFC with hard rock（limestone）as rock aggregate are higher than those of SCC with the same strength grade.2.The cube compressive strength of RFC has obvious size effect,that is,the cube compressive strength of RFC decreases with the increase of specimens size.3.The compressive strength,splitting tensile strength and elastic modulus of A test bin are lower than those of B test bin,indicating that the compressive strength,splitting tensile strength and elastic modulus of RFC decrease with time,but its compressive strength still meets the strength requirements of C15 RFC.（2）The compressive strength test data of RFC（using soft rock（sandstone）as rock aggregate）in C project were collected.It is found that:1.The RFC compressive strength of C project is lower than the SCC strength of the same strength grade,which is only 60%of the SCC compressive strength,which does not conform to the RFC research conclusion of hard rock as rock aggregate.However,its average compressive strength is 1.46 times of the design value of C15 RFC strength,which meets the strength grade requirements of C15 concrete,indicating that the sandstone fully meets the strength requirements of the C15 RFC dam.2.Comparing the compressive strength of A and B test bins,it is found that the compressive strength of RFC decreases with the decrease of the compressive strength of rock aggregate.（3）The RFC large-size specimens with 14 years interval were cut and polished into standard impermeability specimens in the stone processing factory,and the impermeability grade test and relative permeability test were carried out.The test results were close,indicating that the RFC permeability did not change greatly with time.However,because the impermeability specimen is cut and polished,the internal structure of the specimen is more or less destroyed.Therefore,this paper suggests that the test instrument should be improved or more advanced methods should be adopted to carry out the impermeability test of RFC large specimens.（4）The bore-hole pressure test data of 9 RFC dams are collected and converted into permeability coefficient.Compared with the permeability coefficient(10^-8)converted from RFC actual engineering design impermeability grade W6,the number difference of magnitude of the two is 10^-2～10^-3.In order to ensure the safety of the project,after comprehensive consideration,this paper suggests that magnitude of permeability coefficient should be 10^-6 in the design and calculation of seepage of RFC dam,which can provide reference for engineering design.（5）RFC is regarded as a three-phase composite material,and a two-dimensional random aggregate model of RFC is established to simulate the elastic modulus of RFC.Compared with the experimental results,the relative error is within 4%,which proves that the model has certain reliability in predicting the elastic modulus.On this basis,the elastic modulus of RFC in C project is predicted to be 32.69 GPa by this model.The elastic modulus of RFC with a rockfill rate of 60%is also predicted to be36.90 GPa,which can provide reference for engineering design.（6）The finite element seepage theory is used to simulate and analyze the steady seepage field of RFC two-dimensional homogeneous dam.The simulation results show that different permeability coefficients and different thickness of impermeable layer（0m～2m）have important influence on the seepage distribution of RFC dam.In particular,the thickness of the impermeable layer can effectively reduce the pressure head.Considering that the permeability coefficient of the RFC actual engineering field test is large,and there is no corresponding specification for the seepage of the RFC project,in order to ensure the seepage safety of the dam,this paper suggests that the thickness of the impermeable layer should be appropriately increased in the RFC dam project.