| Earth-rockfill dams have the advantages of low investment,fast construction,strong adaptability to the foundation and good seismic performance,and have been widely used in our country.In recent years,the earth-rockfill dams in our country have reached 300 m level.As the height of the dam increased,the crushing degree of the rockfill particles inside the dam increased.Large amount particle crushing increased the deformation.Excessive and uncoordinated deformation led many problems,such as cracks and destruction of the antiseepage system.Meanwhile,most high dams located in the areas with complex geological environments and frequent earthquakes.The seismic load also caused the crushing of rockfill materials and increased the deformation of the dam.Therefore,studying the deformation characteristics of rockfill materials under static and dynamic loads was a prerequisite for the safety evaluation of earth-rockfill dams.At present,the deformation characteristics of rockfill materials under static and dynamic loads were mainly measured by indoor triaxial tests.Due to the large particle size of the prototype rockfill materials,it was necessary to scale down the grading curve of the prototype rockfill materials.Engineering experience showed that when the parameters obtained from indoor tests were used to calculate the deformation of high earth-rockfill dams,the calculated value was usually lower than the field measurement.Therefore,adopted the parameters without considering size effect to calculate the dam deformation would overestimate its safety.The discrete element method can easily obtain the internal structure of the sample at any time,and the size of the numerical sample is not limited,which provides the possibility to study the mechanical properties and size effects of rockfill materials on a meso scale.Based on this,this paper adopted the discrete element method to simulate the force and deformation of the numerical sample of rockfill materials.The mechanical parameters of particle contacts were obtained by fit the indoor conventional large triaxial tests,etc.,and the rationality of mechanics parameters related to particle size was verify further by comparing the simulated results and the indoor super large triaxial tests.The deformation characteristics and size effect law of rockfill materials under static and dynamic loads were further studied.The main research contents of this thesis were as follows:(1)Considering the size-related particle strength,the stress and strain tensors of samples with different sizes were analyzed with particle crushing as a link from the point of particle.The conversions of stress-strain curves for samples with different sizes were verified,and the particle size correlations for parameters of Duncan-Chang E-B model were deduced.The results showed that the stress-strain relationship of samples with larger particles for crushable materials could be predicted based on the size-related strength of single particle and stress-strain curves of samples with smaller particles.The rationality of this calculation method was verified by comparing the predicted curves with the experimental curves for samples with different particle sizes.The size effect formulas of parameters in Duncan-Chang E-B model were deduced.It was found that the parameters of φ0,K and Kb had size effects,while the parameters of Rf,n,mb,and △φ were invariant or had no significant size effect.The parameters of n and mb reflecting the compressive hardening.The ratio between the maximum particle size of the prototype sample and that of scaled sample should be limited to 15 or less.(2)The bond rolling resistance model was formed by add a restriction at the rotation direction on the basis of the contact bonding model.The principle of exact scaling law for the bond rolling resistance model was introduced.On this basis,the correlation particle strength and particle size was proposed.The single particle strength tests were simulated for rockfill particles with different sizes.The simulated results showed that the size effect of particle strength could be well reproduced by linking bond strength to contact radius.Two methods of simulating particle crushing were selected to study the size effect for samples with different sizes.The particle size correlation of particle strength were introduced into the numerical model.The simulation results showed that the larger sample suffered more serious particle crushing,had smaller peak internal friction angle and more volumetric contraction deformation.The parameters of Duncan-Chang E-B model for numerical samples with different sizes were found to have the similar law with the analytical model.(3)The wetting mechanism of rockfill materials was embodied in three aspects:the softening of deformation modulus,particle strength decrease and the lubrication of contact points by water.The DEM parameters of the dry and saturated rockfill materials were determined according to the single-particle strength tests and the indoor tests under dry and saturated conditions.The wetting process could be simulated by transforming the DEM parameters linearly from the dry condition to saturated condition with a constant stress state.The wetting deformation of the large-sized sample was larger than that of the small-sized sample under the consolidated drained triaxial tests and stress path tests with constant stress ratio.The magnitude of the wetting deformation was greatly affected by the characteristic particle size of the sample,confining pressure and the stress ratio during wetting.Thecharacteristic particle size and confining pressure had the similar effects on both the wetting axial and volumetric strains,while the stress ratio had more significant effect on the wetting axial strain.(4)The dynamic elastic modulus of rockfill materials was simulated by considering particle shape and particle breakage.The irregular particle shapes used hexagonal closed packing with different random combinations.The dynamic response of rockfill materials under different confining pressures were simulated and the influence of compactness on dynamic elastic modulus was studied.The simulation results were in good agreement with laboratory test results.Under the same stress condition,the dense sample had higher effective coordination number and went through less particle breakage.The dynamic elastic modulus decayed slowly with the dynamic strain increasing. |
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