【目的】沿海城市轨道交通主要穿越海相深厚软土,需要大量使用冻结法施工,而该地区典型土层热物理特性是冻结法设计的关键依据。研究土质、冻融条件等因素对海相人工冻土冻结温度、热物理性质和冻融性质的影响可为该地质条件下的隧道施工提供基础资料。【方法】选取宁波地区3种典型土层,即淤泥质黏土、粉质黏土和砂质粉土,开展冻结温度和热物理参数测定,以及封闭与开放系统下冻胀融沉试验。【结果】3种土层冻结温度为-0.43～-0.23 ℃,且以砂质粉土的较高,粉质黏土的次之,淤泥质黏土的较低; 不同土层热物理性质不同,但其常温土的导热系数和容积热容量大小呈现一致性,表现为砂质粉土最大,粉质黏土次之,淤泥质黏土最小; 冻土的导热系数、容积热容量和导温系数均大于常温土,冻土导热系数为常温土导热系数的1.37～1.77倍,且颗粒越粗差异越大; 各土层冻胀率和融沉系数相差较大,冻胀率较大的土层其融沉系数也较大,表现为淤泥质黏土＞粉质黏土＞砂质粉土; 开放系统补水冻结过程下各土层冻胀率和融沉系数分别为封闭系统冻结过程不补水工况下冻胀率和融沉系数的1.23～1.88倍和1.21～1.84倍。不论是开放系统还是封闭系统,海相土体各土层的融沉过程相似,可分为缓慢融沉、快速融沉和稳定融沉3个阶段。【结论】海相土体的冻结温度、热物理性质和冻融性质与其土质、状态和冻融条件等因素密切相关,在进行海相土体冻结法设计与施工时,应充分考虑其物理特性的差异性。
Abstract
【Objective】 In Ningbo City, China, since the rail way mainly goes through marine deep soft soils, the artificial freezing method was widely used during the construction. The thermal physical properties of typical soil layers in this area are the thermotical foundation for the design of freezing method. The study of the thermal physical properties of typical marine soil in this area could provide the design of freezing method with some references, promoting the application of the freezing method in the area.【Method】Taking the typical soil layer of mucky clay, silty clay and sandy silt in Ningbo City as the research samples, the tests of freezing temperature, thermal physical parameters and frost heave and thawing settlement in closed and open systems were conducted. The effects of soil, freezing and thawing conditions on the freezing temperature, thermal physical properties and freezing/thawing properties of marine artificial frozen soil were studied. 【Result】The results showed that the freezing temperatures of the three types of soils were ranged from -0.43 to -0.23 ℃(descending in the order of sandy silt, silty clay, mucky clay). The thermal physical properties of different kinds of soils were different, but the values of thermal conductivities of soils at natural temperature were substantial consistent with that of the volumetric heat capacities. It was showed that the sandy silt was the largest, the silty clay was the second, and the mucky clay was the smallest. The thermal physical properties of different kinds of soils were different. The thermal conductivity, volumetric heat capacity and thermal diffusivity of frozen soil were all higher than that of soil at natural temperatures. The thermal conductivity of frozen soil was about 1.37-1.77 times of that of soil at natural temperature. The larger the soil particles, the greater the difference of thermal conductivity between the frozen soil and soil at natural temperature. The frost heaving ratio and thawing settlement coefficients of three kinds of soil were quite different. The higher the frost heaving ratio of soil, the larger the thawing settlement coefficient(descending in the order of mucky clay, silty clay, sandy silt). The frost heaving ratio and thawing settlement coefficient of the soil in the open system were 1.23-1.88 and 1.21-1.84 times of the value of the soil in the closed system.No matter the freezing and thawing conditions were open system or closed system, the process of thawing settlement of each soil layer was similar. Thawing process could be divided into three stages of slow thawing settlement, rapid thawing settlement and stable thawing settlement. 【Conclusion】The freezing temperature, the thermal physical properties and freezing-thawing properties of marine soils were closely related to the soil, the state and the freezing-thawing conditions. In the design and construction of artificial freezing method of marine soil, the difference of thermal physical properties should be fully considered.
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基金
基金项目:国家自然科学基金项目(51478226); 江苏高校优势学科建设工程资助项目(PAPD); 宁波轨道交通有限公司科研资助项目(2015)
第一作者:杨国清(ygq0426@qq.com)。*通信作者:杨平(yangping@njfu.edu.cn),教授。
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