Effect of Sediment Depth on the Compression Behavior and Collapse Behavior of Intact Loess
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摘要:
通过非饱和一维固结仪对比研究黑方台地区沉积深度为10 m（HFT10 m）和30 m（HFT30 m）原状黄土的持水特性、非饱和压缩特性及湿陷特性，揭示应力历史和历史上的水文环境对原状黄土的持水特性、非饱和压缩特性和湿陷特性的影响机制.利用压汞实验和电镜扫描分别测试了原状黄土的孔径分布特征及颗粒排列方式，便于为黄土持水曲线、压缩特性和湿陷特性的结果进行辅助分析.研究结果表明：HFT30 m试样的进气值较HFT10 m试样的进气值大，这可以用压汞实验的结果解释，HFT10 m试样相对于HFT30 m试样具有更大的大孔隙峰值对应的孔隙尺寸. 对于不同沉积深度试样的压缩性而言，在相同的吸力下，HFT10 m试样相对于HFT30 m试样有更低的塑性压缩系数. 在吸力低于100 kPa时，HFT10 m试样相对于HFT30 m试样有更低的屈服应力；当吸力大于100 kPa时，HFT30 m试样相对于HFT10 m试样有更高的屈服应力. 黄土的压缩特性不仅与试样的上覆压力有关，还与试样的基质吸力、饱和度和颗粒之间的胶结程度有关. 在相同的基质吸力下，其饱和度越大其结构更容易在应力的作用下屈服. 对于不同沉积深度黄土的湿陷性试验结果表明黄土的湿陷系数随着轴向应力的增加而增加，并且随着轴向应力的进一步增加，湿陷系数有减小的趋势. 在本研究给定的压力水平下（1~1 400 kPa），在相同的轴向应力下，HFT10 m试样相对比HFT30 m试样有更低的湿陷系数.上述结果表明，黄土的水力特性、压缩特性和湿陷特性均会受到沉积深度及历史赋存环境的影响.
Abstract:Comparative study of the water retention behavior, unsaturated compression behavior and collapse behavior of the sediment depth of 10m and 30m intact loess deposited in the Heifangtai area. To investigate the effect of stress and hydraulic history on the water retention behavior, unsaturated compression behavior and collapse behavior. Mercury intrusion porosimeter (MIP) and scanning electron microscopy (SEM) were used to evaluate the microstructure of two different sediment loess. The result shows that the sample of HFT30 m has a greater air entry value than the sample of HFT10 m, this is because HFT30 m loess has a smaller dominated size for large pores than HFT10 m loess and hence exhibits a larger (air entry value, AEV). For the compression behavior, the HFT30 m loess has larger compression index than the HFT10 m. The yield stress increased with the increase of suction, however, the increased rate of yield stress decreased obviously with the further increase of suction. When the suction was larger than 100 kPa, the yield stress of HFT10 m was smaller than that of HFT30 m; however, with the suction decreasing to smaller than 100 kPa, an unexpected result is observed that the yield stress of HFT30 m was smaller than that of HFT10 m. Overall, the experiment results from compression tests on the two unsaturated loess samples with different depths demonstrated that the effect of suction, saturation and overburden pressure was of great significance to the compression behaviors of unsaturated intact loess. For the collapse behavior, both the HFT10 m loess and HFT30 m loess exhibit that the collapse volumetric strain increases with the increase of net vertical stress, and then decreases slightly with the increase of net vertical stress. Furthermore, the HFT10 m behaved a larger collapse volumetric strain under the same net vertical stress than HFT30 m loess.
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Key words:
- sediment depth /
- unsaturated loess /
- compression behavior /
- collapse behavior /
- geotechnical engineering
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图 3 原状试样的SEM图片
a.HFT10 m放大200倍；b.HFT10 m放大1 000倍；c. HFT30 m放大200倍；d. HFT30 m放大1 000倍
Fig. 3. SEM pictures of natural loess
图 6 不同沉积深度黄土的非饱和压缩曲线
Fig. 6. The compression curve of unsaturated loess
a.HFT30 m; b. HFT10 m
图 7 黄土的塑性压缩系数与吸力的关系
Fig. 7. Variation of plastic compression parameter with suction of two different sediment depth
图 8 测试黄土屈服应力与吸力的关系
Fig. 8. Relationship between yield stress and suction of tested loess
图 9 HFT10 m和HFT30 m黄土湿陷特性
Fig. 9. The collapse behavior of HFT10 m and HFT30 m
a. HFT10 m; b. HFT30m
图 10 原状黄土湿陷系数随竖直应力的变化
Fig. 10. The evaluation of collapse volumetric strain with net vertical stress of intact loess
表 1 两种原状的基本物理力学特性
Table 1. Physical properties of the two tested loess
性质 测量值 HFT10 m HFT30 m 液限(%) 26.4 28.5 塑限(%) 17.8 18.3 颗粒相对密度 2.71 2.71 初始含水量(%) 10.5 11.2 干密度(g/cm3) 1.33 1.37 孔隙比 1.04 0.97 黏粒(%) 8 8 粉粒(%) 85 79 砂粒(%) 7 13 
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表 2 实验方案及目的
Table 2. Test programs and objectives
系列 实验目的 备注 一 不同沉积深度的持水特性 脱湿路径 二 不同沉积深度的非饱和压缩特性 s=0，50，100, 200, 300和400 kPa 三 不同沉积深度的湿陷特性 s=50和400 kPa
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表 3 持水曲线VG模型的拟合参数
Table 3. VG model parameters of the two samples
试样 孔隙比 拟合参数 R2 Ss Sre α m HFT30 m 0.97 1.001 0.234 0.030 0.679 0.996 HFT10 m 1.04 0.969 0.229 0.035 0.718 0.996
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