振动效应对铁路道砟剪切性能影响的离散元数值模拟

铁路道砟在传递移动列车载荷时会产生明显振动及接触迁徙行为，从而诱发道床的破碎劣化及非均匀沉降变形，道砟材料的抗剪性能研究对于碎石道床动力学行为及维养评估非常重要。为进一步探究铁路道砟的剪切力学特性，基于Minkowski Sum理论构造了扩展多面体单元，采用三维Voronoi切割算法生成了非规则扩展多面体道砟颗粒。通过最小投影方法对单元进行粒径识别和筛选，建立了符合铁路道砟级配要求的扩展多面体道砟模型数据库。对比了不同法向应力下铁路道砟准静态直剪试验及离散元模拟结果，验证了扩展多面体道砟接触参数的合理性。在此基础上，开展了振动效应下的道砟动态直剪离散元模拟研究，分析了振动角度、幅值及频率对道砟材料抗剪性能的影响。结果表明：构造的扩展多面体道砟离散元模型能够较好地反映非规则道砟间的强咬合互锁接触作用，并有效模拟直剪过程中的剪切应力–应变的变化及剪缩–剪胀行为。正则化下不同法向应力对应的铁道道砟剪切强度更适合采用幂函数拟合表示。振动场的存在会明显降低道砟颗粒的抗剪性能。当振动方向与剪切方向一致时（振动角度为0°），道砟的剪切强度被明显削弱；随着振幅及频率的增大，道砟颗粒的剪切强度也会显著降低。该研究表明在实际碎石道床性能评估中，需要更多地关注铁路道砟的动态抗剪性能。

NUMERICAL SIMULATION WITH DISCRETE ELEMENT METHOD FOR VIBRATION EFFECT ON SHEAR PROPERTIES OF RAILWAY BALLAST

Railway ballast produces significant vibration and contact migration behaviour when transferring moving train loads, which induces breakage deterioration and non-uniform settlement deformation of the ballast bed. The research on the shear resistance of ballast materials is important for the dynamic behaviour and maintenance assessment of the ballast layer. To further investigate the shear mechanical properties of railway ballast, dilated polyhedron element was constructed based on Minkowski Sum theory in the discrete element method, and the irregular dilated polyhedron ballast particles were generated by three-dimensional Voronoi algorithm. A dilated polyhedron ballast model database that meets the railway ballast grading requirements was established by identifying and screening the particle size using the minimum projection method. The results for the quasi-static direct shear test and discrete element simulation of railway ballast under different normal stresses were compared to verify the rationality of contact parameters between the dilated polyhedron ballast elements. On this basis, the dynamic direct shear simulation of railway ballast under vibration fields was carried out to analyze the influence of vibration angle, amplitude and frequency on the shear performance of ballast material. The results show that the constructed dilated polyhedron ballast model can better reflect the strong occlusal and interlocking contact behaviours between irregular ballast materials. Meanwhile, the shear stress–shear strain and shear dilatancy (shrinkage) properties can also be well-modelled during the direct shear process. The shear strength of railway ballast corresponding to different normal stresses under regularization is better represented by a power function. Besides, the vibration field significantly reduces the shear resistance of ballast particles. When the vibration direction is the same as the shear direction (0° vibration angle), the shear strength of the ballast aggregates was significantly weakened. As the amplitude and frequency increase, the shear strength decreases significantly. This study demonstrates the need to pay more attention to the dynamic shear resistance of railway ballast in the performance assessment of the actual ballast bed.