Study On Strength Behaviors And Constitutive Model Of Rockfill Materials Considering Gradation And Particle Breakage

There are more and more high earth-rock dams over 200 meters high in China with the development of technology.Rockfill materials has the characteristics of convenient collection from local sources,lower deformation,and higher strength,which is widely applied to construct the dam.Particle breakage will cause the change of initial particle size distribution under earthquake or complex stress,affecting the safety and stablility of the high earth-rock dam.Particle breakage will also result in the settlement and volumetric deformation of rockfill dam.It can also cause the cracking and crushing of the concrete face of rockfill dam and the damaging of anti-seepage system of the high earth-rock dam.However,the study on the influence of strength and deformation and critical state of rockfill materials considering the initial particle size distribution and particle breakage is not comprehensive.The systematic researches about single-particle strength characteristics,one-dimensional compression characteristics,shear deformation characteristics,critical state characteristics,and plastics constitutive model of rockfill materials are investigated combining experimental research with theoretical analysis.The main research contents and results in this study can be summerized as follows:(1)Through the single particle crushing tests of the rockfill materials particle with different particle size,the effect of particle size on single-particle strength and the relationship between the characteristic strength and surviving probaliliy were investigated.And then,the strength distribution characteristics of single-particle could be also counted combining Weibull distribution.It could be obtained from the results that the peak force of single-particle increases with particle size increasing.On the contrary,the peak stress drops down with an increase in partice size,implying a significant size effect.The surviving probability were decreasing with the increase of particle size at a given characteristic stress.After sieving the collected broken single particle of rockfill materials,the fractal dimension,particle strength,and crushing energy of the single particle based on the size effect were analyzed.It could be found that the particle strength and crushing energy of rockfill material could be obtained from the fractal dimension.And the greater crushing energy existed in the larger particle size of the tockfill materials.(2)The grain assemblies were aggregated by single particle.The one-dimensional compression tests with different particle size and and sample size under different termination normal stress were carried out to investigate the compression characteristics and particle breakage of rockfill materials based on the results of the single particle crushing tests.The relationship among void ratio,relative particle breakage index,input work and normal stress were discussed.The relationship between the void ratio and normal stress could be expressd by an exponential function.And then,the compression index could be given by Weibull modulus.The yield stress drops with an increase in particle size.And the yield stress could be obtained from the single particle characteristic strength.The phenomenon of particle breakage was more obvious as the normal stress increased.The gradation of the rockfill materials moved to the upper left.And then,the gradation curve gradually reached the final fractal dimension.The correlation among the relative particle index and the input work with normal stress was analyzed.A function could be established to express the relationship between relative particle breakage index and input work under one-domensional compression condition.(3)Through the large-scale triaxial shearing tests,the laws about the strength and deformation were systematically investigated under the different initial gradation curves and confining pressures conditions.It could be summized the variation laws about the deviatoric stress,stress ratio,peak stress,friction angle and peak friction angle with the uniformity coefficient and confining pressure.The results showed that the confining pressure increasing,the deviatoric stress and peak stress also increasing when the same initial gradation condition.Yet,the stress ratio,friction angle and peak friction angle had a opposite trend:the condining pressure increasing,the values of three parameters decreasing.And under the same confining pressure and different particle size distribution condition,the deviatoric stress,stress ratio,peak stress,friction angle and peak friction angle all escalate with the increase of initial uniformity coefficient.(4)Through analyzing the particle breakage of the rockfill materials,the effects of the initial particle size discribution and particle breakage evolution on the mechanical properities were investigated based on the results of the large-scale triaxial shearing tests.The critical state characteristics of rockfill material with gradation and particle breakage evolution were also discussed.The results showed that the gradation shifts towards upper left with the increasing of confining pressure,which could cause the absolute breakage amount and fractal dimension increasing.A new particle breakage index,B_Gr,could be proposed considering the effect of gradation.The relationship between the new relative particle breakage index and input work could be established by a function.And then,the critical state of rockfill materials was also investigated considering the initial gradation and particle breakage in the p-q plane and e-(p/p_a)^? plane,implying that the critical state lines shifted downward with an increase in initial uniformity coefficient and relative particle breakage index in the e-(p/p_a)^? plane.A unified critical state line considering the gradation and particle breakage evolution could be proposed.A three-dimensional unified critical state theory considering the grading and particle breakage evolution could be also established.(5)Based on the three-dimensional critical state theory of rockfill materials,a state-denpendent plastics constitutive model of rockfill materials considering particle size discribution and particle breakage evolution was established under the critical state theory and bounding surface plastic theory frame by introducing the dilatancy stress ratio parameters and boundary surface stress ratio parameters.It also modified the traditional dilatancy equation and plastic modulus by introducing the initial particle size distribution and particle breakage parameters.The materials parameters could be obtained through calculation and analysis,which were suitable for the presented constitutive model.The predicted results of the constitutive model were compared with the results of large-scale triaxial shear tests to verify the rationality of the proposed constitutive model rockfill materials.