基于离散单元法的道砟循环加载双轴试验研究

Study on Biaxial Cyclic Loading Tests on Railway Ballast Using Discrete Element Method

为从微观上分析列车循环荷载作用下道砟强度和刚度变化以及塑性变形的发展,用离散单元法模拟其在一次及二次加载条件下的双轴试验,分析2种情况在不同围压下道砟的力学特性并进行比较。结果表明:(1)第一次加载完成后,偏应力-轴向应变曲线表现为弱应变软化型或应变硬化型,其形态主要取决于围压高低;体应变-轴向应变曲线包括剪缩和剪胀2个阶段,剪缩阶段比较短。(2)第二次加载完成后,不同围压的偏应力-轴向应变曲线均为硬化型,道砟整体强度和刚度减小,塑性变形发展迅速;试验过程中,道砟颗粒一直处于剪胀状态。

The paper analyzes - at micro level-the changes in ballast strength, ballast stiffness as well as the development of plastic delbrmation under cyclic loading. Thanks to the discrete element method, the paper simulates the biaxial compression tests under the first and the second round of Ioadings, after which the mechanical perfbrmance of the ballast for both scenarios are put under comparison. The results show that after the first round of loading, the curves of deviatoric stress and axial strain show either the softening of the weak strain or strain hardening, which is mainly decided by the confining pressure applied. The curves of volumetric strain and axial strain show two stages of change - shear contraction and shear dilation with the former lasting for a shorter period of time comparatively. Besides, after the second round of loading, all the curves of deviatoric stress and axial strain under different confining pressures show the trend of hardening, in other words the overall strength and hardness of the ballast are declining while the plastic deformation develops at rapid speed. The ballast remains in the state of shear dilation throughout the process.