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Study on volume changes and strength characteristics of expansive soil under complex boundary conditions
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摘要: 季节性冻土地区的渠基土易受现场复杂环境的影响，从而影响渠道安全运行。以北疆典型渠道为背景，开展湿干、冻融及其耦合循环条件下渠基膨胀土的体变特性和抗压强度试验研究，探讨不同循环边界条件、不同循环次数下渠基土的变形特征和强度特性。试验结果表明：在湿干循环过程中，试样体积变幅在4次湿干循环后趋于恒定；在冻融循环过程中，试样的体积变幅随冻融循环次数的增长而逐渐减小；在耦合循环过程中，试样的体变特性受湿干效应和冻融效应的综合影响，发生“冻胀融沉”和“冻缩融胀”的临界饱和度约为70%，同时耦合循环中的湿干过程对试样在后续冻结、融化过程中的体变有一定的弱化作用。耦合循环条件下试样的抗压强度衰减最为显著，7次耦合循环后，试样的抗压强度降低了46.9%~59.1%。湿干循环和冻融循环条件下试样的抗压强度衰减程度则与饱和度相关。研究结果可为北疆膨胀土输水渠道的建设与维护提供参考。Abstract: The soil in seasonally frozen soil regions is easy to be affected by the coupling environment, which is related to the canal operation. Taking the typical canals in Northern Xinjiang as background, the experimental study on the volume changes and strength of expansive soil under wet-dry (WD), freeze-thaw (FT) and coupled wet-dry-freeze-thaw (WDFT) cycles was carried out. The deformation and strength characteristics of expansive soil under the different boundary conditions and cycles are discussed. The results show that the volume changes of samples tend to be constant after four WD cycles. During the FT cycles, the volume change of samples decreases with the increasing FT cycles. In the coupled WDFT cycles, the volume changes of samples are affected by the combination of WD effect and FT effect. The saturation of approximately 70% may be the critical saturation for the occurrence of “frost shrinking and thaw expanding” and “frost expanding and thawing shrinking”. The WD process in the coupled WDFT cycles has a certain weakening effect on the volume changes of samples during the subsequent FT process in the coupled WDFT cycles. Meanwhile, the strength of samples decreases significantly under the coupled WDFT cycles. After 7 coupled WDFT cycles, the sample strength decreases by 46.9%~59.1%. The attenuation degree of strength is related to saturation under WD cycles and FT cycles. The research results can provide a basis for the construction and maintenance of expansive soil canals in Northern Xinjiang.
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Key words:
- wetting-drying cycles /
- freezing-thawing cycles /
- canal /
- expansive soil /
- compressive strength
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图 3 试样体积变化率随冻融循环次数变化的曲线
Figure 3. Curve of volume changes with freezing-thawing cycles
图 4 试样体积变化率随耦合循环次数变化的曲线
Figure 4. Curve of volume changes with coupled wetting-drying-freezing-thawing cycles
图 5 不同S值下湿、干、冻、融过程中试样体积变化曲线
Figure 5. Curves of volume changes in wetting, drying, freezing and thawing processes with disserent S
图 6 不同边界条件下试样应力-应变关系曲线
Figure 6. Curves of strain-stress relationship with different boundary conditions
图 8 不同边界条件下试样抗压强度随循环次数的变化曲线
Figure 8. Curves of strength variation with cycles under different boundary conditions
表 1 土样基本特性
Table 1. Basic properties of soils
最大干密度/（g·cm−3） 最优含水率/% 液限/% 塑限/% 自由膨胀率/% 小于某粒径的质量百分比/% <0.005 mm <0.075 mm <0.250 mm <0.500 mm <2.000 mm 1.70 18.4 18.4 52.6 71.0 31.5 70.1 82.6 90.2 100 
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