Effectiveness of post-grouting on the vertical response improvement for extra-long bored piles: case studies on field tests

The current engineering practice has shown that post-grouting improves the vertical bearing capacity of bored piles. However, some engineers are concerned about the effectiveness of post-grouting in the context of extra-long bored piles. At present, the effect of pile tip post-grouting on the side resistance of these extra-long bored piles remains uncertain. This paper investigated the effects of post-grouting on the compressive and uplift responses of extra-long piles, drawing on case studies from seven field static load tests. It proposed a mechanism for pile tip post-grouting across various bearing layers to enhance the side resistance of extra-long piles by reinforcing the soil beneath the pile tip. Additionally, it outlined the effectiveness and limitations of post-grouting in improving the vertical response of extra-long piles situated in different bearing layers. The analytical results indicated that post-grouting at the pile tip improved the strength of the soil beneath the pile tip. This improvement not only decreased the settlement at the pile tip but also enhanced the side resistance of the pile, especially the side resistance near the pile tip. The effectiveness of pile-tip post grouting in improving pile side resistance is significantly and positively correlated with the reinforcing effect on the soil beneath the pile tip. The effectiveness of post-grouting on the vertical response of extra-long piles can be inconsistent under working loads. Therefore, it is crucial to improve the quality of post-grouting construction in these piles to enhance the overall effectiveness of post-grouting improvements.