Study On Grading Evolution And Deformation Of Rockfill Materials Considering Particle Breakage

The rockfill dam is widely used in the hydropower project,for its easier material selection,lower cost and better foundation adaptability.With the development of dam-construction technology,the height of rockfill dam is increasing too.In the high rockfill dam,particle breakage of the rockfill materials(RFMs)occurred frequently,due to the high stress.It would change the gradation and mechanical properties of RFMs,cause the volume compression of the RFMs,result in cracking and crushing of the concrete face of the rockfill dam(CFRD)and lead to the impervious system failure.Traditionally,the mechanical properties of RFMs was studied through the triaxial tests.Due to the limitation of measurements,the particle size distribution(PSD)curve during the test could not be measured directly.The crushing properties of the particles could also not be invested deeply.Meanwhile,due to the size limitation of the instrument,the prototype RFMs could not be tested directly.At present,the test RFMs could only be reduced from the prototype ones.However,there is a great differences between the finite element calculation results(parameters chosen from the triaxial test)and the actual observed values.That would affect the security determinant of the dam.In order to solve the problems above,the crushing and deformation properties of Gushui rockfill material(GRFM)were studied.The main research contents are as follows:(1)Single particle-strength test of GRFM was carried out.The strength of GRFM particles was measured and the crushing particle group was sieved.The test results show that the strengths of particles well obey Weibull distribution and the PSD of the crushing particle group well obeys the Fractal distribution.With the increase of particle size,the particle strength decreases significantly.Size effect on the strength of the particle could be observed clearly.(2)In the numerical simulation of triaxial test of RFMs,a method was proposed to describe the PSD evolution of RFMs.By introducing the size-effect formula of the particle strength,this method could be used to describe the grading evolution of the prototype RFMs.The validity of the model is verified by comparing with the triaxial test results of uniform and non-uniform RFMs.(3)The relationship between crushing parameters and deformation of the test sample was constructed.The simulation of the loading sample-particle crushing-gradation evolution-sample deformation was realized.A numerical simulation method for RFM mechanical test was proposed.By calculating the deformation of reduced-scale sample with the test grading and full-scale sample with the prototype grading and by comparing with test result,the method was verified.Finally,the effect of reduced scale grading on the parameters of Duncan-chang model for the RFMs was discussed.(4)In the numerical simulation of stress and deformation of RFMs.By introducing the time-dependent strength of the rock,a method to simulate the creep of RFMs was proposed.This method could well simulate the uniaxial creep test and the triaxial creep test.All the calculation results were verified through the test results.(5)The micromechanics-based analytical(M-A)model was extended to make it capable of simulating the deformation properties of RFMs under different stress paths.By considering the influence of the mean principal stress on the particle stiffness,the model could well describe the deformation of the specimen under the loading and unloading conditions.By considering the influence of the transitional confining pressures on the dilatancy angle,the model can well reflect the dilatancy of the RFMs.Finally,the validity of the model is verified by comparing with the experimental results.