Effect of Clay Contamination on Stress-Dilatancy Relationships of Ballast Aggregate
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摘要:
列车循环荷载下，铁路地基层中的黏土颗粒会逐渐侵入道砟层，降低道床承载性能. 通过开展一系列大型直剪试验，对黏土脏污质污染下的受格栅加筋道砟集料和未受格栅加筋道砟集料的强度及变形发展、应力-剪胀关系进行了研究. 试验结果表明：随着脏污程度的增加，道砟集料在剪切过程中强度及法向变形均降低；干净道砟集料的应力比与剪胀比呈一阶线性关系，而黏土污染的道砟集料塑性增强，在剪应力峰值状态下剪胀比更高而抗剪强度发展缓慢，导致应力比与剪胀比呈二阶多项式关系；高法向压力下，道砟集料具有更低的剪胀比；黏土脏污质的存在会减小道砟集料的变形破坏速率，但降低了集料的抗剪强度，而格栅的加筋作用可弥补由于黏土脏污引起的强度降低.
Abstract:Clay fines from subgrade would gradually intrude into the ballast layer under cyclic loadings of passing trains, which would reduce the bearing capacity and impede the free drainage of track beds. A series of large-scale direct shear tests were carried out to investigate the strength and deformation characteristics and stress-dilatancy relationship of the geogrid-reinforced and unreinforced ballast contaminated by clay fines. The results showed that the strength and normal displacement of ballast aggregate decrease with an increase in the contamination level. The stress ratio of clean ballast is linear with the dilatancy ratio, while the addition of clay fines would increase the plasticity of the ballast aggregate. For fouled ballast in the peak state of shear stress, the dilatancy ratio of aggregate increases while the shear strength decreases, and a second-order polynomial relationship between stress ratio and dilatancy ratio is observed. Under a higher normal pressure, the aggregates have a lower dilatancy ratio. The reduction in the dilatancy rate and the shear strength of clay-contaminated ballast can be remedied by the inclusion of geogrid in the aggregate.
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图 4 受格栅加筋与未受格栅加筋道砟τs及δn与δs关系
Figure 4. Relationships of shear stress τs vs. shear displacement δs and relationships of normal displacement δn vs. shear displacement δs for geogrid-reinforced and unreinforced ballast
表 1 道砟及黏土脏污质工程性能指标表
Table 1. Engineering properties of clean ballast and clay fines
材料 比重 堆积密度/
（kg·m−3）e ωL/
%ωP/
%D50/
mmCu Cc 道砟 2.66 1432 0.858 39.0 1.15 1.75 黏土 2.70 1178 1.207 42.10 22.40 1.3 24.29 1.34 
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表 2 格栅参数表
Table 2. Mechanical properties of geogrid
参数 规格 孔径形式 双向孔径 55 mm × 55 mm 材料 聚丙烯 2% 应变时抗拉
强度/（kN·m−1）11 5% 应变时抗拉
强度/（kN·m−1）15 峰值抗拉强度/（kN·m−1） 30 屈服点伸长率/% 13
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表 3 试样设置情况表
Table 3. Details of experimental specimens
VCI/% 试样编号 格栅布置 黏土质量/kg 0 S1-1 格栅加筋 S1-2 20 S2-1 格栅加筋 21.70 S2-2 40 S3-1 格栅加筋 43.40 S3-2
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