A study of the influences of freezing temperature and thawing conditions on physical properties of marine soft soil before and after freezing-thawing
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摘要:
海相软土冻融前后物理特性差异是研究人工冻结法工后融沉的关键，本文以宁波典型海相软黏土为研究对象，冷端温度（−5 ℃、−10 ℃、−15 ℃）和解冻条件（强制解冻、自然解冻）为影响因素，在室内模拟软黏土人工冻融过程，定量分析冻融前后物理性质差异，并揭示产生差异的原因。研究表明：冻融作用导致海相软黏土的含水率、干密度、孔隙比、渗透性等物理参数沿冻结梯度方向发生重新分布；随冷端温度每降低1 ℃，含水率、干密度、孔隙比变化程度减小4%～8%；采用强制解冻方式，土体含水率变化程度减小约23%，干密度和孔隙比的变化程度减小约50%；但究其本质，不同冻融条件影响物理参数变化各异的实质为不同条件下水分迁移与相变量不同，探究水分迁移并揭示对物理参数值的影响值得进一步深入研究。海相软土冻融前后物理参数变化与冷端温度及解冻方式密切相关，其变化程度易直接影响工后融沉，在进行海相软土冻结法设计与施工时，应选择合理的冻融方式，减小物理特性的差异性。
Abstract:Difference in physical properties of marine soft clay before and after freezing-thawing is the key to study the thawing-settlement. This paper takes the typical soft clay in Ningbo as the research object, and the temperature (−5 ℃, −10 ℃ and −15 ℃) and the thawing conditions (forced thawing and natural thawing) are considered as the influencing factors. Indoor simulation experiment of freezing-thawing process was conducted to quantitatively analyze the differences in physical properties before and after freezing-thawing and to reveal the cause of the difference. The research results show that freezing and thawing results in the redistribution of physical parameters such as moisture content, dry density, pore ratio and permeability of the marine soft clay along the direction of freezing gradient. With the decrease in the cold junction temperature by 1 ℃, the change degree of water content, dry density and void ratio decreases by about 4% − 8%. When forced thawing is adopted, the change degree of soil moisture content is reduced by about 23%, and the change degree of dry density and void ratio is reduced by about 50%. However, the essential reason that different freezing-thawing conditions have various influences on physical parameters is the different amount of water migration and phase variables under different conditions. Thus, exploring water migration and revealing the effects on physical parameter is worthy of further study. The change in physical parameters of marine soft clay before and after freezing-thawing is closely related to the cold junction temperature and the thawing method, and the degree of change is easy to directly affect thawing-settlement. When designing the freezing method of marine soft clay and constructing, reasonable freezing-thawing methods should be selected to reduce the difference in physical properties.
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表 1 软黏土土样基本物理性质
Table 1. Basic physical properties of the soil samples
类别 含水率/% 密度/（g·cm−3） 比重 液限/% 塑限/% 塑性指数 冻结温度/℃ 平均 37.5 1.87 2.75 41.5 20.1 21.4 −0.40 最大 41.5 1.99 2.76 44.1 22.2 21.9 −0.41 最小 30.5 1.77 2.74 36.7 18.6 18.1 −0.38 
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表 2 试验方案
Table 2. Experiment planning
冷端温度/℃ 解冻条件 物理试验 影响因素 −5
−10
−15自然解冻 密度、含水率、孔隙比、
变水头渗透试验温度 −10 自然解冻
强制解冻密度、含水率、孔隙比试验 解冻条件
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表 3 试样制备与试验方法
Table 3. Specimen preparation schedule
冻融后物理试验 试样尺寸 试样数 解冻方式 冻结条件 含水率、干密度、
孔隙比试验Φ80×100 mm 3 自然解冻 −5 ℃冷端温度冻结 3 自然解冻 −10 ℃冷端温度冻结 3 自然解冻 −15 ℃冷端温度冻结 3 强制解冻 −10 ℃冷端温度冻结 变水头渗透试验 Φ100×50 mm 3 自然解冻 −5 ℃恒温环境冻结 3 自然解冻 −10 ℃恒温环境冻结 3 自然解冻 −15 ℃恒温环境冻结
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表 4 试样冻结稳定时不同高度处温度
Table 4. Temperature of different heights of the sample when the freezing is stable
高度/cm 温度/℃ −5 ℃ −10 ℃ −15 ℃ 9 0.4 −0.5 −1.4 7 −1 −2.8 −4.3 5 −2.3 −5 −7.1 3 −3.5 −7.1 −10 1 −4.5 −9.2 −13.1
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表 5 不同温度渗透试验结果
Table 5. Results of permeability experiment under the influence of different freezing temperatures
土样 渗透系数/（×10−7cm·s−1） 含水率/% 干密度/（g·cm−3） 孔隙比 原状土 4.839 37.43 1.82 1.02 −5 ℃冻融土 9.879 38.69 1.79 1.08 −10 ℃冻融土 11.49 39.07 1.77 1.11 −15 ℃冻融土 18.89 39.25 1.76 1.12
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