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Study on the influence of freeze-thaw cycles on the deformation and mechanical properties of expansive soil
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摘要: 为探究季冻区恶劣气候对不同含水率下渠基膨胀土的胀缩变形和物理力学性质的影响，以北疆阿勒泰地区膨胀土为研究对象，室内模拟了北疆地区实际气候条件的冻融循环试验。基于此，对含水率为12%、16%和20%的膨胀土进行体积变形试验、无侧限抗压强度试验和SEM电镜扫描试验，着重分析了冻融循环作用对膨胀土体积变形和力学特性的影响规律。结果表明：冻融循环过程中，随含水率的增加，试样的体积变形由冻缩融胀向冻胀融缩转变。应力-应变曲线特性与冻融循环次数和含水率都有较大的关系。试样的无侧限抗压强度随着含水率和冻融循环次数的增加而降低，其中以第1次冻融循环最为明显，3次后趋于稳定。函数拟合发现，试样的无侧限抗压强度与冻融循环次数呈明显的自然指数关系。含水率越大，冻融循环作用对土体微观结构的影响越大；土体的孔隙度随冻融循环次数的增加逐渐增大，第1次冻融循环作用最为明显，宏观上表现为冻融循环作用对土体力学性质的劣化影响。Abstract: In order to explore the influence of the severe weather in the seasonal freezing area on the expansion and contraction deformation and physical and mechanical properties of the canal base expansive soil with different water contents, the expansive soil in the Altay area of northern Xinjiang was taken as the research object, and the freeze-thaw cycle test of the actual climatic conditions in northern Xinjiang was performed in the laboratory. Based on this, the volumetric deformation test, unconfined compressive strength test and scanning electron microscope (SEM) test of the expansive soil with moisture contents of 12%, 16%, and 20% were carried out, and the influence of freeze-thaw cycles on the volume deformation and mechanical properties of expansive soil was analyzed emphatically. The results show that during the freeze-thaw cycle, with the increase of water content, the volume deformation of the sample changes from "freeze shrinkage and thaw expansion" to "freeze heave and thaw shrinkage". The characteristics of the stress-strain curve are closely related to the number of freeze-thaw cycles and the moisture content. The unconfined compressive strength of the sample decreases with the increase of the moisture content and the number of freeze-thaw cycles. Among them, the first freeze-thaw cycle is the most obvious, and it stabilizes after three times. The function fitting shows that the unconfined compressive strength of the sample has an obvious natural exponential relationship with the number of freeze-thaw cycles. The greater the water content, the greater the influence of freeze-thaw cycles on the microstructure of the soil; the porosity of the soil gradually increases with the increase in the number of freeze-thaw cycles. The first freeze-thaw cycle has obvious effect, which is manifested macroscopically as the effect of freeze-thaw cycles on the degradation of soil mechnical properties.
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图 1 2013年11月—2014年11月渠道沿线地表气温分布曲线
Figure 1. Surface temperature distribution curve along the channel from November 2013 to November 2014
图 5 冻融循环1、7次后含水率为20%的膨胀土SEM照片（100倍）
Figure 5. SEM photo of expansive soil with 20% moisture content under a magnification of 100 times after freeze-thaw cycle of 0, 1, 7 times
图 6 冻融循环7次后含水率为12%、16%、20%的膨胀土SEM照片（1 000倍）
Figure 6. SEM photo of expansive soil with moisture content of 12%, 16%, 20% after 7 freeze-thaw cycles under 1 000 times magnification
表 1 膨胀土的基本物理性质及矿物组成
Table 1. Basic physical properties and mineral composition of expansive soil
物理性质 矿物组成 液限/% 塑性/% 塑性指数/% 最大干密度/(g·cm−3) 最优含水率/% 蒙脱石/% 石英/% 长石/% 方解石/% 钠长石/% 52.6 18.4 34.2 1.71 18.4 61.5 31.4 6.1 0.5 0.5 
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表 2 函数拟合结果
Table 2. Function fitting result
含水率/% 系数A 系数B 系数C 相关性R2 12 356.260 8 137.340 3 −0.420 3 0.999 0 16 132.301 9 148.206 9 −0.607 7 0.987 2 20 58.835 5 126.488 7 −0.915 2 0.999 8
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