Numerical Simulation Study On Wetting Deformation Characteristics Of Coarse-grained Materials Considering Scalling Effect By PFC

In recent years, with the rapid development of China’s rockfill dams, the engineering characteristics of coarse-grained materials have become particularly important, which act as the main filling material of rockfill dam. Since the coarse-grained materials’particle size are generally large, the existing large lab equipments can not meet the requirements of the prototype materials mechanical test. Through scaling the prototype material grading, the approximate physical and mechanical properties of the material of the prototype can be studied. But the differences between tests and actual values caused by scaling are difficult to grasp. Meanwhile, the wetting deformation and deformation of wet-dry cycles problems of the coarse-grained materials in the rockfill dams have not been solved. In this paper, considering the high cost of lab test, the scaling triaxial test and wet test of coarse-grained materials was simulated by particle flow code PFC, the scale effect and wetting deformation characteristics with consideration of scale effect of the coarse-grained materials have been studied.Firstly, the triaxial test numerical simulations for coarse-grained materials are conducted by using of the conventional BPM model of PFC. The response relationship between meso parameters of numerical model and macroscopic properties of coarse-grained materials has been studied. The results showed that the friction coefficient, bond parameters are positively correlated with peak shear strength of the samples; particles’ elastic modulus, friction coefficient, contact bond shear strength, parallel bond stiffness are positively correlated with deformation modulus of the samples; particles’normal stiffness to shear stiffness ratio, porosity, contact bond normal strength, parallel bond strength are negatively correlated with deformation modulus of the samples; particles’ elastic modulus, normal stiffness to shear stiffness ratio, porosity, contact bond normal strength, parallel bond strength are positively correlated with Poisson’s ratio of the samples; particles’ friction coefficient, contact bond shear strength, parallel bond stiffness are negatively correlated with Poisson’s ratio of the samples.Secondly, based on existing experimental studies, the scaling triaxial tests numerical simulations for coarse-grained materials are carried out by using conventional PFC models and introducing CLUSTER particle model. The effect of scaling methods on the strength and deformation characteristics of coarse-grained materials is studied. The results show that the volumetric strain curves of the numerical simulation and the experiment are quite different; the stress-strain curves of the numerical simulation with introducing CLUSTER particle are in good agreement with the experiment, and the samples got from similar grading method have the maximum peak strength, and the samples got from equal-weight replacement method have the minimum peak strength, and the properties of the samples got from mixing method and elimination method behave between the samples got from similar grading method and equal-weight replacement method; the relationship between the maximum particle size of the samples and the calibrated microscopic parameters of numerical model is studied by using CLUSTER model, it pointed out that with the increase of the maximum particle size of the samples, the calibrated elastic modulus of the particles increased, but the growth rate gradually decreased, and the contacting bond parameter increases linearly. Based on the above relationship, through lab tests for the small samples size, studying the strength of the samples which beyond the test instrument size by numerical simulation becomes possible.Finally, the single-line method and the double-line method wetting test numerical simulations for coarse-grained materials are carried out by using PFC, and the amount of wetting deformation is calculated in different scaling methods, and the wetting deformation characteristics are discussed with considering scale effect. The results show that the wetting deformations calculated in single-line method is significantly greater than that calculated in double-line method, and the wetting deformations increases with the increase of confining pressure; the samples got from similar grading method have the maximum wetting deformations, and the samples got from equal-weight replacement method have the minimum wetting deformations, and the wetting deformations of the samples got from mixing method and elimination method are between the samples got from similar grading method and equal-weight replacement method; with the increase of the maximum particle size of the samples, the wetting deformations increase.