在冻结法施工中掌握冻土的蠕变特性对工程的安全评价至关重要。采用山西某矿井深部黏土,在负温条件下进行原状土单轴压缩试验与分级加载蠕变试验,研究冻结黏土破坏时的形态、一系列温度下的单轴抗压强度与蠕变曲线的形式。试验得出单轴抗压强度随温度降低呈线性变化,同一加载应力下的蠕变值随着温度的降低而减小。引入内变量理论并将应变作为内变量来描述冻土的蠕变特性,分析蠕变与蠕变率取对数的拟合曲线发现两者具有线性关系,进而建立只与温度和加载系数有关的内变量蠕变模型,模型参数可通过拟合曲线确定。将蠕变的计算值与试验结果对比,发现该模型可以较好地反映冻结黏土的蠕变,且模型参数少,便于工程应用。

Safety evaluation of artificial freezing method depends on the creep characteristics of frozen soil. Uniaxial compression test and staged loading creep test were conducted at temperatures below 0 ℃ on undisturbed clay collected from a deep mine in Shanxi Province to study the failure mode and mechanism of the frozen soil as well as the form of uniaxial compressive strength and creep curves at different temperatures. The uniaxial compressive strength varied linearly with the declining of temperature, and the creep value under the same loading stress also decreased with the drop of temperature. In line with the internal variable theory, strain was considered as the internal state variable to describe the creep characteristics of frozen soil. The fitting curve of logarithm of creep and creep rate suggested a linear relationship between them. On such basis, an internal variable creep model that was only related to temperature and loading coefficient was established. Parameters of the model could be determined by fitting curves. The fitting of test data into the model showed that the model could better reflect the creep of frozen clay with less model parameters, and is convenient for engineering application.