基于黏度时变性的桩端压力浆液上返高度模型及工程应用

桩端后压浆浆液上返高度对后压浆桩承载力的计算影响较大。基于幂律型流体的黏度时变性特征，推导了考虑黏度时变性的桩端压力浆液上返的理论计算公式，并给出了参数的确定方法及成层土中浆液上返高度的迭代算法；结合台州湾大桥的接线工程，利用电磁波CT对桩基后压浆的加固效果进行了探测分析。结果表明，采用浆液沿压浆管道阻力损失的拟合值并考虑黏度时变性得到的浆液上返高度的计算结果与实测结果基本吻合且偏于安全，而忽略黏度时变性得到的计算结果偏大，会对后压浆桩的承载力设计造成不利影响。此外，电磁波CT能观测到桩体、水泥浆加固体及土体的分布情况，且能推测出水泥浆液在桩端的扩散范围和沿桩身的上返高度，可用于评价后压浆桩的压浆效果。研究成果可为后压浆桩的设计和效果检测提供参考和指导。

The model of grout migration height for pressured grouting at pile tip based on time-dependent behavior of viscosity and its engineering application

The grout migration height has a remarkable influence on the calculation of bearing capacity for post-grouting pile. Based on the time-dependent behaviors of power-law cement grout, a theoretical expression to calculate upward grout migration along the pile side was proposed with consideration of time-dependent behavior of viscosity. The methods to determine the parameters and to iteratively determine the grout migration height in the layered soils were presented, respectively. Moreover, based on post-grouting project of the connecting engineering of Taizhou Bay Bridge in Zhejiang Province, the reinforcement effect of post-grouting piles was analyzed by means of electromagnetic wave CT. The results show that the predicted results of grout migration height on the basis of fitting value of pressure loss along the grouting pipeline and time-dependent behaviors of viscosity are consistent with measured results, which verifies the rationality of proposed expression for grout migration height. However, an overestimated bearing capacity of post-grouting piles may be obtained when ignoring the influence of time-dependent behaviors of viscosity, which has an unfavorable influence on pile design. Additionally, the electromagnetic wave CT can detect the distribution pattern of the pile, injected grout and soil, and can also deduce the diffusion range of cement grout at pile tip, as well as the grout migration height along the pile shaft, which can be applied to assess the grouting effect of grouted pile. The research results can provide reference and guidance for design and effect detection of post-grouting piles.