Effectiveness of large-diameter combined tip-and-side post-grouted piles in deep fine sand layers: A field test study

This study investigates the effectiveness of combined tip-and-side post-grouting on large-diameter bored piles in deep fine sand layers. Field tests were conducted on nine piles for the Shishou Yangtze River Highway Bridge project. A detailed comparison of pile performance pre- and post-grouting assessed the technique's influence on ultimate bearing capacity and side resistance. The distribution and effectiveness of the cement grout were analyzed using core drilling and the standard penetration test (SPT). An equation correlating post-grouting side resistance with the pre-grouting SPT index ( N SPT ) was established. Results demonstrate a substantial improvement in pile bearing capacity after grouting. Ultimate bearing capacity increased by 76%-152% after grouting. Longer piles on the main bridge exhibited more pronounced enhancement, achieving ultimate capacities 145%-206% higher than those of the shorter approach bridge piles. This is attributed to the greater total cement volume applied along their sides. Critically, combined grouting outperformed side-only grouting, enhancing both side and tip resistance. Core drilling confirmed the spread of cement grout around the piles, confirming the method's effectiveness. SPT results indicated significant increases in the soil N SPT adjacent to the piles following grouting. These findings provide directly applicable data for designing the bridge pile foundations and offer essential guidance for comparable projects in deep fine sand layers.