中文摘要：

环境温度是土体冻结和融化过程中常见的变量。为明确冷却温度对土体冻融循环效应的影响规律,以青藏高原粉质黏土为对象,进行不同冷却温度和冻融次数的冻融循环试验及三轴剪切试验,并测定试样冻融循环后的水分重分布和体积变化特征。结果表明,冻胀和冻缩在冻结过程中是同时存在的,且均随冷却温度的降低而增大,两者正负变形量比例关系的不同是土体冻融循环效应多变的主要原因之一。随着冷却温度的降低,由于冻胀先于冻缩达到极限状态,体积增加量呈先增大、后减小的规律,转折点对应的是冻胀和冻缩在微小温差条件下变形附加量相对大小关系发生改变的临界温度值。破坏强度随冷却温度的变化与干密度一致,呈先减小、后增大的规律,以劣化为主。未冻水含量和水分迁移量均随冷却温度的降低而减小,因此冷却温度越低,破坏强度随冻融次数的变化范围越小,达到新的稳定状态所需的冻融次数也越少。黏聚力和内摩擦角随冷却温度和冻融次数的变化规律可以采用Logistic模型拟合与预测,以方便工程应用。

英文摘要：

In order to study the influence of cooling temperature on the properties of soil subjected to the cyclic freezing-thawing,a set of freezing-thawing tests under the different cooling temperatures and numbers of freezing-thawing cycles were carried out on samples of silty clay from Qinghai—Tibet Plateau. The triaxial shear tests were subsequently conducted on the samples after freezing-thawing under the different confining pressures. The volume increment and the moisture migration inside the samples were measured after one freezing-thawing cycle. Results show that the expansion and contraction exist simultaneously in the freezing process and both increase with the decrease of cooling temperature. The different ratios between the freezing expansion and the freezing contraction are one of the main reasons for different effects of cyclic freezing-thawing. The freezing expansion reach the maximum state earlier than the freezing contraction,so the volume increment increases initially and then decreases as the decrease of cooling temperature. The failure strengths of samples after freezing-thawing are reduced on the whole and vary the same as the dry density does,i.e.,they decrease initially and then increase with the decrease of cooling temperature. The unfrozen moisture content and the amount of moisture migrated both decrease with the decrease of cooling temperature. Hence the range of failure strength changing due to cyclic freezing-thawing becomes smaller when the cooling temperature is lower. The variation of cohesion and internal friction angle versus the cooling temperatures and the numbers of freezing-thawing cycles were fitted with the Logistic model.