以天津地铁盾构端头砂质粉土为研究对象,开展了封闭系统下土体单向冻结试验,对不同冷端温度和不同含水率条件下冻结试样的温度变化与冻胀变形规律进行了研究。此外,通过ANSYS有限元软件对室内土体单向冻结过程进行了数值模拟研究。结果表明:土体初始含水率越高,土体稳定冻结阶段持续的时间越长;砂质粉土的起始冻结温度随土体含水率增大而升高;在封闭单向冻结条件下,土体的冻胀量随含水率增加而显著增大,而冷端温度降低对土体最终冻胀量的影响相对较小;模拟得出的温度变化趋势与室内试验结果基本吻合,但从稳定冻结阶段至缓慢降温阶段存在明显突变;随着冻结时间推移,土层不同深度的竖向冻胀位移均有所增加,越靠近上表面,土层的竖向位移增长越显著;冻结500 min后,土体不同位置的竖向冻胀位移与其深度呈线性关系。
A closed-system unidirectional freezing experiment is conducted on the sandy silt found at the entrance and exit portal of the shield tunnel in Tianjin Metro. The test aims to investigate the temperature variation and frost heave deformation characteristics of frozen specimens under different freezing temperatures and moisture contents. Additionally, a numerical simulation of the unidirectional freezing process of sandy silt is performed using ANSYS finite element software. The test results indicate that: The higher initial moisture content in the soil, the longer duration of the stable freezing stage, and the initial freezing temperature of sandy silt increase with the increase of soil moisture content. Under the closed unidirectional freezing condition, the frost heave of the soil significantly grows with the increase of moisture content, while the influence of lower freezing temperatures on the final frost heave is relatively small. The simulated temperature variation trend corresponds well with the laboratory test results, except for an obvious mutation from the stable freezing stage to the slow cooling stage. As the freezing time progresses, the vertical frost heave increases at different depths within the soil. A more significant vertical displacement can be observed closer to the upper surface soil layer. After freezing for 500 minutes, the vertical frost heave displacement at different positions of the soil is linearly related to its depth.
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