Effects of Soil Unloading and Grouting on the Vertical Bearing Mechanism for Compressive Piles

The present study conducts a series of model cast-in-place piles tests to analyze the vertical bearing characteristics and the grout returned diffusion mechanism along the pile shaft of tip post-grouting piles with different grouting and pile shaft soil unloading conditions. The model test results show that the pile tip post-grouting technology can improve the weak difference in the bearing characteristics and axial force distribution of the pile foundation caused by pile shaft soil unloading. The pile shaft resistance can be improved by the returned grout in the pile shaft. The pile shaft resistance will mainly bear the pile top load when the pile top load and the grouting volume are relatively small, and the pile tip resistance will mainly bear the pile top load with the increases of the pile top load and the grouting volume. The grouting return height increases with the increase in pile shaft soil unloading degree, and the analyzed values of the grouting returned height based on the pile bearing characteristic results are close to the measured values. The grouting diffusion mechanism of the cement on the pile tip and pile shaft soil during the pile tip post-grouting process is revealed.