Research On The Scale Effect Of Coarse Grained Materials Based On Super Large Triaxial Apparatus

As an important engineering material,coarse grained material has been widely used in large scale geotechnical structures such as artificial islands,airport high fills,embankment and rockfill dams owing to its properties of good water permeability,high filling and compation density,and strong anti-liquefaction capacity.In order to meet the deformation and stability safety evaluation of such large structures,scholars around the world have carried out a large number of experimental studies on the deformation and strength characteristics of coarse grained materials.Due to the development of vibratory rolling construction technology,the size of the coarse grained material rolled on the project site is obviously larger than the maximum allowed by the laboratory test.The maximum particle size of the coarse grained material after on-site rolling is about 2/3 of the rolling thickness(rolling thickness 800mm?1000mm).As a result,the prototype coarse grained materials could only be largely scaled to meet the requirment of the laboratory experiments.The change of the deformation characteristics of the coarse grained material after scaling is a conundrum in the experimental research of coarse grained materials.The maximum particle size tested by the conventional large-scale triaxial instrument is usually only 60mm.The researches show that there is a great difference between the finite element analysis results(paramters from the conventional large triaixal test)and the actual measured value and it is generally believed that the scale effect is one of the main reasons for this difference.As a consequence,the scale effect of coarse grained material is one of the key issues that must be considered in the engineering design and numerical analysis of artificial islands,airport high fills,embankment and rockfill dams.However,the research results on scale effect of coarse grained material is usually based on the triaxial tests with maximum particle size of 60mm.Due to the lack of large scale test verification,the deformation characteristics and its mechanism between the prototype and the scaled material remains unclear.To this end.the scale effect of the static and dynamic characteristics of coarse grained materials were studied based on the super large triaxial apparatus newly developed by the Key Laboratory of Engineering Seismic Research Institute of Dalian University of Technology.The influences of the scale effect on the peak strength,static modulus,particle breakage,critical state,dynamic shear modulus,damping ratio,and residual deformation characteristics of coarse grained materials are mainly studied.On this basis,the research results of the scale effect were applied to the construction numerical analysis of the Aertashi gravel-rockfill dam project.The rationality of the model parameters considering the scale effect based on the results of the superlarge triaxial test has been verified by comparing with the actual measured results.The main research content and conclusions of this study are as follows:(1)A series of conventional large scale and super large scale consolidated drained triaxial tests were conducted on Rumei and Aertashi blasting materials to study the scale effect in static monotonic tests.The results show that the peak shear strength,tangent modulus and dilatancy behavior of the blasting material decreased with the increasing maximum particle size.The shear strength and initial modulus could be well simulated by introducing the maximum particle size into the shear strength and initial modulus equations.(2)According to the static monotonic test results,the influence of scale effect on the parameters of Duncan Zhang E-? model.E-B model,Tsinghua K-G model and Shenzhujiang model were studied.The results show that the scale effect has a same influence on the above model parameters for both Rumei blasting and Aertasch blasting materials.By introducing the the maximum particle size into the elastic modulus.bulk modulus,and failure ratio of the Duncan Zhang E-B model,the results of different maximum particle sizes can be simulated.(3)The influence of scale effect on the particle breakage characteristic of blasting material was analyzed using Rumei and Aertashi blasting with the Pyramid dam material in the literature.The results show there exists a hyperbolic relation between the input plastic work and particle breakage for samples with different maximum particle size.The relation between the input plastic work and particle breakage shifts upward as the maximum particle size increased,which means the particle breakage enhanced with the increasing maximum particle size at the same input plastic work.A particle breakage equation considering maximum particle size was established according to the test results.(4)The influence of stress paths and scale effect on the critical state characteristic of blasting material were analyzed using Rumei blasting.The results show that the critical state of Rumei blasting was irrespective of loading stress paths.The critical state line of Rumei blasting was dependent on the maximum particle size in e-(p'/pa)?space.The intercept of the critical state line in e-(p'/pa)? space for different maximum particle size was almost the same.The critical state line in e-(p'/pa)? space rotated clockwise as the maximum particle size increased.The critical state equation considering the maximum particle size of blasting material was established.(5)A series of conventional large scale and super large scale cyclic triaxial tests were conducted on Aertashi blasting material to study the scale effect of the dynamic properties of blasting material.The results show that the maximum dynamic shear modulus and damping ratio increased with the increasing maximum particle size.The residual axial and volumetric strain increased with the increasing maximum paritlce size.The influence of scale effect on the parameters of Shenzhujiang equivalent viscoelastic model was quantified.The Shenzhujiang and DLUT residual deformation model were modified by introducing the maximum particle size into the model.(6)The influence of particle size on the particle shape of Rumei and Aertashi blasting was investigated.The results show that the Fourier based particle shape and angularity index decreased with the increasing particle size,which means the blasting particles become more round and less sharp with the increasing particle shape.The size effect of particle shape could be one of the factors for the scale effect of blasting materials.(7)The scale effect of Aertashi gravel was studied through a series of super large and common large triaxial tests.The influences of scale effect and constitutive models on the numerical analysis after construction stage of Aertashi CFRD were studied based on the test results by comparing to the actural measured results.The results show that the gravel and blasting materials of Aertashi present opposite trends on the deformation characters between super large triaxial and conventional large triaxial tests.The peak shear strength,tangent modulus and dilatancy of the Aertashi gravel increased with the increasing particle size.The displacement simulated in model parameters considering scale effect are closer to the monitoring data than the one without considering scale effect.However,the displacement,especially the horizontal displacement simulated in Duncan Chang E-B model is much larger than the measured value.The distribution and value of the displacement simulated in parameters considering scale effect of the generalized plasticity model coincide with the measured value.