Discrete element virtual triaxial test of ballast penetration into subgrade soil sample
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摘要: 采用离散元法(DEM)从宏细观角度研究了有砟轨道道砟嵌入对路基土变形特性的影响；基于三维结构光扫描系统对道砟颗粒外形进行重构，实现道砟颗粒的精细化建模；基于DEM软件PFC3D V6.0建立高度为600 mm、直径为300 mm的道砟嵌入试样与纯土试样三轴计算模型；通过有限差分法(FDM)与DEM耦合，实现三轴围压柔性加载，分别对2种试样进行三轴试验模拟；对比分析了道砟嵌入试样与纯土试样的模拟结果，明确道砟嵌入对路基土变形特性的影响。研究结果表明：围压为30 kPa时，道砟嵌入试样峰值强度为257 kPa，纯土试样峰值强度为199 kPa，相比于纯土试样，道砟嵌入会使土体承受荷载的能力降低；剪切结束时纯土试样体应变为-3.24%，道砟嵌入试样为-14.59%，道砟嵌入试样剪胀效应更为明显；纯土试样与道砟嵌入试样侧向变形机理不同，纯土试样中部产生鼓胀变形是因为其中部区域不受约束，颗粒可自由运动，道砟嵌入试样土样表层发生侧向鼓胀是因为道砟-土界面处发生的道砟嵌入对表层土颗粒向两侧挤压的排挤作用；2种试样土颗粒配位数变化趋势一致，均表现出随轴向应变先增加、后减小、最后趋于平缓的趋势，但纯土试样土颗粒配位数明显高于道砟嵌入试样；纯土试样力链沿轴向发展且分布均匀，道砟嵌入试样会在道砟-土接触界面出现明显接触力集中。Abstract: The discrete element method (DEM) was used to study the effect of ballast penetration in ballasted tracks on the deformation characteristics of subgrade soil from both macroscopic and mesoscopic perspectives. The shape of ballast particles was reconstructed based on a three-dimensional structured light scanning system, and the refined modeling of ballast particles was realized. Triaxial computational models of a ballast penetration sample and a pure soil sample with a height of 600 mm and a diameter of 300 mm were established based on DEM software PFC 3D V6.0. The finite difference method (FDM) was coupled with DEM to realize the flexible loading of triaxial confining pressure. The simulations of triaxial tests were conducted separately for both samples. The simulation results of the ballast penetration sample and pure soil sample were compared and analyzed to clarify the influence of ballast penetration on the deformation characteristics of subgrade soil. Research results show that at a confining pressure of 30 kPa, the peak strength of the ballast penetration sample is 257 kPa, whereas that of the pure soil sample is 199 kPa. Compared with the pure soil sample, ballast penetration reduces the load bearing capacity of subgrade soil. At shear termination, the volumetric strain of the pure soil sample is -3.24%, while that of the ballast penetration sample is -14.59%, indicating a more pronounced shear dilation effect in the ballast penetration sample. The lateral deformation mechanism of the pure soil sample is different from that of the ballast penetration sample. Bulging deformation in the middle of the pure soil sample occurs because the central region is unconstrained, allowing particles to move freely. The lateral bulging of the surface soil in the ballast penetration sample occurs because ballast penetration at the ballast-soil interface exerts a squeezing action on surface soil particles on both sides. The trend of soil particle coordination number variation is consistent for both types of samples, showing an initial increase followed by a decrease with axial strain and ultimately reaching a plateau. However, the soil particle coordination number of the pure soil sample is significantly higher than that of the ballast penetration sample. The force chains in the pure soil sample develop along the axial direction and are evenly distributed, whereas noticeable contact force concentration occurs at the ballast-soil interface in the ballast penetration sample.
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Key words:
- railway engineering /
- ballast track /
- DEM simulation /
- virtual triaxial test /
- ballast penetration /
- flexible loading
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图 5 某重载铁路轨道-路基结构及选取的道砟嵌入试样
Figure 5. Heavy haul railway track-subgrade structure and selected ballast penetration sample
图 11 道砟嵌入试样三轴试验模拟流程
Figure 11. Triaxial test simulation flow of ballast penetration sample
图 13 道砟和路基土细观参数标定结果
Figure 13. Calibration results of mesoscopic parameters of ballast and subgrade soil
图 14 加载结束后道砟嵌入试样和纯土试样的形态
Figure 14. Morphologies of ballast penetration sample and pure soil sample after loading completion
图 15 道砟嵌入试样与纯土试样的偏应力-轴向应变响应
Figure 15. Deviatoric stress-axial strain responses of ballast penetration sample and pure soil sample
图 16 道砟嵌入试样与纯土试样的体应变-轴向应变响应
Figure 16. Volumetric strain-axial strain responses of ballast penetration sample and pure soil sample
图 17 纯土试样与道砟嵌入试样的破坏形态
Figure 17. Failure modes of pure soil sample and ballast penetration sample
图 19 不同轴向应变时纯土试样颗粒位移
Figure 19. Particle displacements of pure soil sample in different axial strains
图 20 不同轴向应变时纯土试样颗粒转动角度
Figure 20. Particle rotation angles of pure soil sample in different axial strains
图 21 不同轴向应变时道砟嵌入试样颗粒位移
Figure 21. Particle displacements of ballast penetration sample in different axial strains
图 22 不同轴向应变时道砟嵌入试样颗粒转动角度
Figure 22. Particle rotation angles of ballast penetration sample in different axial strains
图 23 纯土试样与道砟嵌入试样中土颗粒的平均配位数
Figure 23. Average coordination numbers of soil particles in pure soil sample and ballast penetration sample
图 24 不同轴向应变时纯土试样的力链分布
Figure 24. Force chain distributions of pure soil sample in different axial strains
图 25 不同轴向应变时道砟嵌入试样的力链分布
Figure 25. Force chain distributions of ballast penetration sample in different axial strains
表 1 接触模型参数
Table 1. Parameters of contact model
接触类型 参数 取值 道砟
(赫兹接触模型)G1/GPa 2.0 υ1 0.18 μ1 0.9 土颗粒
(Hill接触模型)G2/MPa 11.5 υ2 0.25 μ2 0.5 ψ/kPa 70 土颗粒与道砟
(赫兹接触模型)G12/MPa 22.7 υ12 0.25 μ12 0.5 橡胶膜 Y/MPa 1.1 T/mm 2.5 ρ/(kg·m-3) 930 全局参数 局部阻尼 0.7 
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