Experimental Study on Effect of Geogrid on Direct Shear Behavior of Contaminated Ballast
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摘要:
为探究土工格栅对受黏土污染道砟力学特性的影响，通过对4种法向压力、3种黏土污染程度下土工格栅加固的道砟试样进行一系列直剪试验，对比分析土工格栅对道砟试样剪切强度和剪切变形的影响，研究了考虑黏土污染情况下土工格栅对道砟的加固效果. 研究结果表明：土工格栅增大了洁净及受黏土污染道砟试样的剪切强度，当污染指标VCI （void contamination index）为20%时提升峰值剪切强度最大达到24%；道砟剪切强度表现出典型的非线性特征，非线性强度准则拟合参数与道砟污染程度利用指数函数拟合，拟合结果可作为实际工程受污染道砟强度估计的依据；土工格栅可减小试样的最大剪胀量，同时可减小约0.7°～3.7° 的峰值剪胀角，并且在VCI为20%时土工格栅加固的效果最为明显.
Abstract:In order to investigate the effect of geogrid on the mechanical properties of clay-contaminated ballast, a series of direct shear tests were carried out on geogrid-reinforced ballast specimens under four normal pressures and three degrees of clay pollution. The effects of geogrid on the shear strength and shear deformation of ballast specimens were compared and analyzed. The reinforcement effect of geogrid on ballast with consideration of clay pollution was studied. The results show that the geogrid can increase the shear strength of clean and clay-contaminated ballast samples, and the peak shear strength reaches 24% when the void contamination index (VCI) is 20%. Ballast shear strength exhibits typical non-linear characteristics, and the relationship between fitting parameters of non-linear strength criterion and pollution degrees can be fitted by an exponential function. The fitting results can be used as the basis for strength estimation of contaminated-ballast in practical engineering. Meanwhile, geogrid can reduce the maximum dilatancy of the sample; it can also reduce the peak dilatancy angle by about 0.7°～3.7°, and achieve its maximum reinforcement effect at the VCI of 20%.
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Key words:
- geogrid reinforcement /
- clay fouling /
- direct shear test /
- shear properties /
- ballast
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图 7 法向位移与水平位移关系曲线
Figure 7. Vertical displacement versus horizontal displacement curves
图 8 峰值剪胀角与污染程度关系
Figure 8. Relationship between the peak friction angle and VCI under various normal stress
表 1 试验材料参数表
Table 1. Physical properties of test materials
材料 堆积密度ρ/（kg•m−3） 比重 d 孔隙比 e 含水率ω/% 液限/% 塑限/% 道砟 1432 2.66 0.858 黏土 1178 2.70 1.292 22.2 42.1 22.4 
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表 2 土工格栅参数表
Table 2. Physical and technical properties of geogrid
材料 类型 孔径/mm 空隙率/% 极限抗拉强度/（kN•m−1） 聚丙烯 双向方形格栅 55 × 55 81 30
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表 3 试验方案
Table 3. Experiment schemes
试验组别 试样编号 VCI/% 法向压力/kPa 有格栅 1 号 0 15、35、55、75 2 号 20 3 号 40 无格栅 4 号 0 15、35、55、75 5 号 20 6 号 40
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表 4 峰值剪切强度数据
Table 4. Results of peak shear stress
试样编号 σn=15 kPa σn=35 kPa σn=55 kPa σn=75 kPa 1 号 80.28 130.28 155.44 178.19 2 号 74.17 115.28 141.53 169.03 3 号 58.19 94.03 128.89 153.47 4 号 70.42 94.10 140.28 164.93 5 号 54.44 84.44 136.04 149.72 6 号 46.81 67.64 111.39 141.94
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