Thawing behavior of frozen soil with high ice content under the action of high-power heating rod
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摘要: 为探究高含冰量冻土在高温作用下的融化过程和水热变化，在负温环境箱内将干土、冰晶、水按配合比制成温度为-1.5 ℃，体积含冰量分别为20%、30%、40%和50%的4种冻土，然后利用自制的高功率加热棒对4种高含冰量冻土进行了预融对比试验，并通过传感器对冻土解冻过程中土体的温度和体积含水量进行实时监测，分析了加热棒作用下冻土温度和水分随时间的变化规律以及融化速率；通过现场试验验证了高功率加热棒用于预融深层高含冰量冻土的有效性和可靠性，并利用静力触探试验(CPT)判断了土体的融化范围。研究结果表明：加热棒作用下冻土的融化过程可以分为3个阶段，即冰水相变融化阶段、升温阶段和降温阶段；冻土融化由温度梯度和湿度梯度下共同作用引起的水热迁移主导，土体的最高温度随着含冰量和径向距离的增加逐渐减小；高温作用对径向为0~5 cm处的融土水分具有显著驱动作用，在加热时间内径向为5 cm处冻土的含水量在达到设计含水量之后逐渐减小；冻土在0~5 cm范围内的融化速率远大于其他范围且融化速率随着径向距离和含冰量增加而大幅减小；通过水分场判断冻土的融化时间和范围具有一定的滞后性，其会低估冻土的融化速度和范围，建议融化试验过程中通过温度响应时间来判断冻土冻融状态；通过CPT可以快速判断现场预融过程中冻土的融化范围。Abstract: To explore the thawing process and hydrothermal changes of frozen soil with high ice content under high-temperature conditions, four types of frozen soil with a temperature of -1.5 ℃ and ice volume content of 20%, 30%, 40%, and 50% were prepared in a sub-zero environmental chamber where dry soil, ice crystals, and water were mixed according to specific proportions. Subsequently, self-designed high-power heating rods were utilized to conduct pre-thawing comparative experiments on these four types of high-ice-content frozen soil, and sensors were employed to monitor real-time temperature and volumetric water content changes during the process. After that, under the action of heating rods, the variation patterns of frozen soil temperature and water content over time as well as the thawing rate of the frozen soil were analyzed. On this basis, field experiments were conducted to verify the efficacy and reliability of high-power heating rods for the pre-thawing of deep high-ice-content frozen soil. Additionally, the cone penetration test (CPT) was employed to determine the thawing range of the soil. Research results show that the thawing process of frozen soil can be divided into three stages under the influence of heating rods: the ice-water phase change thawing stage, the temperature rise stage, and the cooling stage. The thawing of frozen soil is primarily driven by hydrothermal migration jointly induced by temperature and moisture gradients, with the maximum soil temperature gradually decreasing as ice content and radial distance increase. High-temperature effects significantly drive moisture movement in thawed soil within the radial range of 0-5 cm, where the water content of frozen soil at 5 cm radial distance gradually decreases after reaching the designed water content during heating. The thawing rate of frozen soil within the 0-5 cm range is significantly higher than that in other ranges, and it decreases sharply with increasing radial distance and ice content. Determining thawing time and range through moisture fields shows certain hysteresis, underestimating the actual thawing speed and range. It is recommended to assess the freeze-thaw state of frozen soil during thawing experiments by monitoring the temperature response time. The CPT tests can be used to quickly determine the thawing range of frozen soil during field pre-thawing processes.
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图 4 高功率加热棒融化冻土设备与模型
Figure 4. High-power heating rod and model for frozen soil thawing
图 6 深度25 cm处不同含冰量冻土沿径向的温度随时间变化规律
Figure 6. Temperature changes of frozen soil with different ice contents at 25 cm depth over time in radial direction
图 7 不同含冰量冻土在不同位置的土壤最高温度
Figure 7. Maximum soil temperatures of frozen soil with different ice contents at different locations
图 8 深度为25 cm处不同含冰量冻土沿径向的未冻水体积含量随时间变化规律
Figure 8. Variation of volume content of unfrozen water in frozen soil with different ice contents at 25 cm depth over time in radial direction
图 9 不同含冰量冻土在不同位置的初始融化时间
Figure 9. Initial thawing time of frozen soil with different ice contents at different locations
图 10 不同含冰量冻土在不同位置处的完全融化时间
Figure 10. Complete thawing time of frozen soil with different ice contents at different locations
图 11 20%含冰量冻土在不同时刻的融化范围
Figure 11. Thawing range of frozen soil with 20% ice content at different times
图 12 不同含冰量冻土在不同范围内的融化速率
Figure 12. Thawing rates of frozen soil with different ice contents in different ranges
图 16 不同加热时间下土壤沿深度的锥尖阻力和侧壁摩阻力
Figure 16. Cone tip resistance and sidewall frictional resistance of soil along depth at different heating times
表 1 试验用土的基本物理力学参数
Table 1. Physical and mechanical parameters of test soil
土粒相对体积质量 干重度/(kN·m-3) 最佳含水率/% 液限/% 塑限/% 土壤类型 2.62 18.0 15.8 22.6 16.4 粉砂土 
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表 2 不同含冰量冻土的配合比
Table 2. Mixing ratios for frozen soil with different ice contents
编号 含冰量/% 试样质量/kg 干土质量/kg 水质量/kg 冰砂质量/kg 1 20 136.5 122.8 9.8 3.8 2 30 135.0 115.7 9.3 10.0 3 40 133.6 109.3 8.7 15.5 4 50 132.4 103.6 8.3 20.5
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