Modeling of Grout Returned Height for Postgrouting at Pile Tip Considering the Soil Unloading and Time-Dependent Behavior of Cement Viscosity Effects

Postgrouting at the pile tip can improve the behavior of pile shaft resistance through the grout returned along the pile shaft. The soil radial unloading effect that existed in the bored pile shaft soil and the cement viscosity with time-dependent behavior affect the grout diffusion. A grout returned height model for postgrouting at the bored pile tip considering the soil unloading effect and time-dependent behavior of cement viscosity was proposed to analyze the grout returned diffusion behaviors. The reliability of the grout returned height model was compared and verified with a series of model bored pile tests and the measured results of the field case. The analysis results showed that considering the influence of pile shaft soil unloading for bored piles and the time-dependent behavior of cement viscosity in the grout returned height model is essential for analyzing the grout returned diffusions. A parametric study with the proposed model was performed, and the effects of soil unloading degree, the grout flow rate, the grouting pressure, and the pile scaling effect on the grout returned height were analyzed.