| Meso parameters in the model in this paper are calibrated by orthogonal test method. The static and dynamic biaxial tests on ballast are simulated by particle flow software PFC2D with the Hertz-Mindlin contact model to study the influence of confining pressure, particle size distribution and particle shapes on the mechanical properties of crushed stone ballast. The static characteristics of conclusions based on the tests are summarized as following:Strain hardening characteristics can be found in the stress-strain relationships of ballast under various confining pressures. When the axial strain is the same,the deviatoric stress, initial modulus, peak strength and failure strain increase with the confining pressure increasing, and more obvious shear contraction can be found at bigger confining pressure. The shear strength envelope of ballast is nonlinear, internal friction angle decreases with increasing vertical stress. The stress-strain curves of the same gradation ballast are strain hardening. The influence of gradation of ballast on the stress and strain is not obvious. The more uniform the particles, the more obvious the shear contraction. Ballast whose engineering properties are better has smaller failure strain and greater brittleness index. However, good engineering properties of ballast do not produce high shear strength. The stress-strain curves of ballast with different shapes are strain hardening. The peak strength, brittleness index and initial modulus keep increasing with particle shape coefficient and dilatancy is more obvious.The dynamic characteristics of conclusions based on the tests are summarized below:The skeleton curve of ballast under different confining pressure is strain hardening. The dynamic strain increases and the dynamic elastic modulus decreases with the amplitude of dynamic stress increasing at the same confining pressure. The energy consumption of ballast in the dynamic loading case increases gradually. Dynamic stress and dynamic elastic modulus increase with the confining pressure under the same dynamic strain condition. The capability of ballast aggregate resisting plastic deformation is very strong, so ballast has good seismic performance and energy dissipation capacity. The positive correlation of resilient modulus with confining pressure and the first stress invariant are well showed, which the relationship line is a nonlinear growth. With the increase of confining pressure, the bearing capacity and non-deformability of ballast can well be represented.The dynamic stress-strain curve of the same gradation ballast is strain hardening. The dynamic elastic modulus decreases rapidly with the dynamic strain increasing and finally being relative stable. The better the engineering properties of ballast, the lower the dynamic modulus of elasticity when dynamic strain is very small. But the particle gradation almost does not affect the dynamic modulus of elasticity when the dynamic strain is very large (greater than0.8%). Comprehensive analysis shows that, the engineering properties of particle size of ballast-lin the new railways are better than that of the particle size of the extra ballast, the density of particle size of ballast-1in the new railways is higher and the dynamic modulus of elasticity of it is greater. Ballast hysteretic curves more reflect the particle slip under the condition of small cyclic stress ratio, with the increase of cyclic stress ratio, the plastic deformation capacity, seismic performance and energy dissipation capacity enhance. The more superior the ballast gradation, the denser the aggregate. The graded fine ballast has bigger resilience modulus and stronger ability to resist permanent deformation. The resilience modulus of the same gradation ballast and the first stress invariants has better positive correlation. The resilient modulus increase nonlinearly with the increase of the first stress invariants.The dynamic stress-strain curve of the same shape ballast is strain hardening, the greater the deviatoric stress, the greater the modulus of resilience. The particle whose shape is closer to the quadrilateral and angular has greater dynamic modulus of elasticity and modulus of resilience. The positive correlation of resilient modulus of different shape ballast with confining pressure and the first stress invariant are well presented and the relationship line is a nonlinear growth. |
