冻土地基桩基础承载特性温度与流变响应试验

为揭示冻土温度、流变特性对桩基承载性能的作用效应,进行温度、流变响应试验分析,采用自行设计的大型冻土桩基承载性能试验装置,开展了不同地温、不同加载过程下桩基承载特性模型试验,分析了轴力与侧摩阻力的温度、流变响应。结果表明:地基温度对桩基刚度具有显著影响,温度较高（约-3 ℃）时,刚度仅为温度较低（约-6 ℃）时的1/10。其次,温度较低时,轴力沿深度迅速衰减,侧摩阻力呈上大下小,桩体上部（约1/3）主要承载；温度较高时,轴力分布平缓,深部侧摩阻力发挥程度相应提高。再者,流变效应对侧摩阻力的发展、变化存在显著影响,持荷阶段流变导致的侧摩阻力降低逾200 kPa。此外,流变效应亦受地基温度及荷载水平的影响:地温较高时,流变导致的侧摩阻力松弛近乎初值的50%；荷载水平升高时,流变效应呈现先增大后减小的趋势。冻土地基中桩基础承载性能具有显著的温度、流变响应,实际工程设计、运维必须予以考虑,研究结果可为工程实践提供理论支撑。

Tests on thermal and rheological responses on bearing characteristics of pile in frozen ground

To reveal the effect on the bearing characteristics of piles from thermal and rheological properties of frozen soil, experimental analysis on thermal and rheological responses was conducted. Using a self-designed large-scale test apparatus, several laboratory model tests on the bearing characteristics of piles in the frozen ground were performed under different temperatures and loading processes. The thermal and rheological responses of axial force and shaft resistance were analyzed. Results show that, firstly, the ground temperature has a significant effect on the foundation stiffness. With a higher ground temperature (about -3 ℃), the pile stiffness reduces to only 1/10 of that when the temperature is lower (about -6 ℃). Secondly, with the lower ground temperature, the axial force decreases rapidly along the depth, and shaft resistance is large on the top and small on the bottom, that is, the upper part of the pile ( about upper 1/3) bears the major load. On the contrary, with the higher ground temperature, the axial force distribution becomes relatively gentle along the whole pile length, and the shaft resistance on the deeper pile obtains an increasing exertion correspondingly. Thirdly, the rheological effect has a significant influence on the development and variation of shaft resistance. Due to the rheological effect, shaft resistance has a significant decrease of more than 200 kPa in the load-holding stage. Furthermore, the rheological effect is also affected by ground temperature and load level. When the ground temperature increases, the relaxation of shaft resistance resulting from the rheological effect is nearly 50% of the initial value. When the load level increases, the rheological effect presents a developing trend that increases first and then decreases. The bearing characteristics of piles in frozen soil have significant thermal and rheological responses, which must be considered in practical engineering design, operation, and maintenance. The results of this study can provide theoretical support for engineering practice.