Study on mechanical response and mechanism analysis of bored piles under different grouting combinations in coastal regions

The bearing capacity of piles in coastal soft soil regions is of critical importance. Combined tip and side grouting is a practical technique for effectively enhancing pile capacity. To specifically meet the demands of superstructure loading, engineers are particularly concerned about the improvement in pile capacity under different combined grouting methods. In this study, four field test piles were utilized to investigate various combinations of tip and side grouting. By comparing static load test results before and after grouting, the effect of different side grouting ring configurations on the axial bearing characteristics of piles was analyzed. Additionally, the borehole coring tests and standard penetration tests (SPT) were conducted to reveal the grouting mechanisms and the extent of its influence. Furthermore, numerical simulations were employed to explore the effect of different tip grouting parameters on pile bearing capacity. The results indicate that combined grouting significantly enhances pile capacity by mobilizing both tip and side resistance. Increasing number of side grouting rings led to an improvement in pile capacity by 67.98 %–107.94 %. Moreover, in coastal silty clay layers, side grouting primarily occurs in the form of fracture grouting, whereas tip grouting forms a cement-gravel mixture through compaction and infiltration. Finally, numerical simulation results validated that increasing the strength of the tip grouting material has a limited effect on enhancing pile capacity, whereas expanding the grout diffusion range is more effective in improving pile capacity.