冻土区桩基础冻胀过程中钢筋与混凝土黏结性能劣化机制研究

Study on Deterioration Mechanism of Bond Performance Between Rebar and Concrete During Frost Heaving of Pile Foundation in Frozen Soil Area

冻土区钢筋与混凝土之间的黏结性能对温度的响应更为敏感,并且桩内部因钢筋与混凝土之间的线膨胀系数差异引起的温度应力不容忽视,因此有必要对其进行研究。首先通过分析并建立计算模型,得到模型中沿桩基横截面的温度分布。接着,推导了温度应力的计算公式。然后基于弹塑性厚壁圆筒理论,推导了在温度梯度影响下钢筋与混凝土的黏结强度计算公式。最后给出了桩的直径、混凝土保护层厚度以及钢筋与混凝土的线膨胀系数应满足的要求。以工程实例对桩基础的各个土层状况进行分析,在假设土的干容重、冻土的总含水量、地中热流值、冻土的导热系数不变,季节冻融层为强冻胀土的条件下,分别对单桩和群桩基础的冻拔问题进行了验算。结果表明:得到的临界承载力模型可以为寒区冻土层中桩基础的稳定性评估提供数值分析依据。

The bond performance between rebar and concrete in the frozen soil area is more sensitive to temperature,and the temperature stress caused by the difference of linear expansion coefficient between rebar and concrete cannot be ignored,thus,it is necessary to study it.Firstly,the temperature distribution along the cross section of pile foundation is obtained by analyzing and establishing the calculation model.Then,the calculation formula of temperature stress is deduced.Then,based on the elastic-plastic thick wall cylinder theory,the calculation formula of bond strength between rebar and concrete under the influence of temperature gradient is derived.Finally,the requirements of pile diameter,concrete cover thickness and linear expansion coefficient between rebar and concrete are given.Based on the analysis of each soil layer of pile foundation with engineering examples,under the assumption that the dry unit weight of soil,the total water content of frozen soil,the heat flow value in the ground,and the thermal conductivity of the frozen soil remain unchanged,and the seasonal freeze-thaw layer is strong frost heaving soil,the freezing and pulling problems of single pile foundation and group pile foundation are checked respectively.The results show that the critical bearing capacity model can provide numerical analysis basis for the stability evaluation of pile foundation in frozen soil layer in cold region.