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Experimental studies on freeze-thaw cycles of expansive soil based on orthogonal design
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摘要: 南水北调南阳段膨胀土位于季节性冻土区域，易受冻融循环的影响。以南阳膨胀土为研究对象，对不同含水率、冻结温度、冻融循环次数的膨胀土试样进行变形测量和无侧限压缩试验。试验发现，含水率对膨胀土力学性质影响较大，含水率越高，强度与弹性模量衰减量越大；冻结温度对试样体积有较大影响，尤其是-10 ℃。根据显著性分析理论，研究含水率、冻结温度、冻融循环次数以及各因素间交互作用对膨胀土物理力学性质影响的显著性。结果表明，含水率对膨胀土力学性质影响最明显，含水率和冻结温度间的交互作用对强度影响较为显著；冻结温度对膨胀土体积变化影响最大，含水率和冻融循环次数的交互作用对体积变化有一定影响。在研究冻融循环条件下膨胀土物理力学性质时，不仅要考虑单一因素的影响，还应综合考虑各种因素交互作用的影响。Abstract: The expansive soil in the Nanyang section of the South-to-North Water Diversion Project is situated at the seasonal frozen soil region, which is easy to be affected by the freeze-thaw cycles. The freeze-thaw cycles will also change the structures of the expansive soil and affect its physical and mechanical properties, which will make a notable impact on the construction of the works. In order to study the factors and interactions on the physical and mechanical properties of the expansive soil, the Nanyang expansive soil was taken as a case study. The deformation measurements and unconfined compressive tests were carried out for understanding the physical and mechanical properties of the Nanyang expansive soil samples under the conditions of different water contents, freezing temperatures and freeze-thaw cycles. The testing results show that the water content has a great influence on the mechanical properties of the expansive soil: the higher the water content, the greater the strength and elastic modulus decline. The freezing temperature has a great influence on the volume change, especially -10 ℃. Some studies of the significant influence of the water content, freezing temperature, the number of freeze-thaw cycles as well as the interaction between different factors on the physical and mechanical properties of the expansive soil were made on the basis of the theory of significance analysis. The study results show that the impact of the water content on the mechanical properties of the expansive soil is the most remarkable, and the interaction between the freeze temperature and water content has a significant impact on the unconfined compressive strength. And the freezing temperature is the most significant influence on the volume change, and the interaction between the water content and freezing-thaw cycles has a certain influence on the volume change. Therefore, we should not only consider the influences of a single factor, but also consider the interactions of various factors in studying the physical and mechanical properties of the expansive soil under the conditions of the freeze-thaw cycles.
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Key words:
- expansive soil /
- freeze-thaw cycles /
- stress-strain curves /
- strength /
- elastic modulus /
- volume change /
- significance analysis
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图 1 冻结温度-10 ℃下膨胀土试样应力应变曲线
Figure 1. Stress-strain curves of expansive soil samples under freezing temperature of -10 ℃
图 2 冻结温度-10 ℃及含水率20%下无侧限抗压强度
Figure 2. Unconfined compressive strength under freezing temperature of -10 ℃ and water content of 20%
图 3 冻结温度-10 ℃及含水率20%下弹性模量
Figure 3. Elastic modulus under freezing temperature of -10 ℃ and water content of 20%
图 4 冻结温度-10 ℃及含水率20%下体积变化率
Figure 4. Volume change under freezing temperature of -10 ℃ and water content of 20%
表 1 膨胀土基本物理指标
Table 1. Physical properties of expansive soil
比重G 最大干密度
ρdmax/(g·cm-3)最优含水率
ωop/%塑限
ωp/%液限
ωL/%塑性指数
Ip/%自由
膨胀率/%颗粒成分/% < 0.075 mm < 0.250 mm < 0.500 mm < 1.000 mm < 2.000 mm 2.72 1.78 20 22.5 42.6 20.1 67 10.9 38.2 59.3 96.0 100.0 
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表 2 考虑交互作用的表头设计
Table 2. Top-of-form design considering interactions between three factors
因素 1 2 3 4 5 6 7 8 9 10 11 12 13 A B (AB)1 (AB)2 C (AC)1 (AC)2 (BC)1 (BC)2
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表 3 F检验的临界值Fα(f1, f2)
Table 3. F test criticial values Fα(f1, f2)
显著性水平α Fα(f1, f2) f1=2，f2=8 f1=4，f2=8 0.10 3.11 2.81 0.05 4.46 3.84 0.01 8.65 7.01
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表 4 考虑交互作用时无侧限抗压强度影响因素的显著性检验
Table 4. Significance tests of unconfined compressive strength factors considering interactions
方差来源 平方和 自由度 F值 显著性 含水率A 303 886.03 2 372.14 ** 冻结温度B 8 648.93 2 10.59 ** 冻融循环次数C 9 131.23 2 11.182 ** AB 4 804.38 4 3.98 * AC 2 513.13 4 2.47 BC 972.35 4 0.58 误差 3 266.33 8 总和 333 222.38 26
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表 5 考虑交互作用时弹性模量影响因素的显著性检验
Table 5. Significance tests of elastic modulus factors considering interactions
方差来源 平方和 自由度 F值 显著性 含水率A 640.18 2 110.40 ** 温度B 17.66 2 3.05 冻融循环次数C 28.78 2 4.96 * AB 11.93 4 1.03 AC 16.79 4 1.45 BC 4.78 4 0.41 误差 23.20 8 总和 743.32 26
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表 6 考虑交互作用时试样体积影响因素的显著性检验
Table 6. Significance tests of volume factors considering interactions
方差来源 平方和 自由度 F值 显著性 含水率A 0.56 2 1.43 冻结温度B 14.05 2 35.81 ** 冻融循环次数C 1.90 2 4.85 * AB 0.46 4 0.59 AC 2.29 4 2.91 (*) BC 0.89 4 1.13 误差 1.57 8 总和 21.72 26
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