The open grouting of bridge cast-in-place piles is difficult to control the grouting area, grouting pressure and grouting amount. The stability of grouting effect is poor and the bearing capacity of single pile fluctuates greatly. In order to improve the reliability of post grouting of pile foundation, a new type of composite post grouting technology at pile bottom is proposed. By installing hollow annular steel plate capsules at pile bottom, the soil at pile end is strengthened through the composite inside and outside of the capsule. To reveal the improvement effect on the bearing capacity of pile foundation, composite post-grouting operation of two test piles was conducted at S340 overpass bridge project of Fenshi Expressway under construction. The dynamic changes of grouting pressure, grouting volume and pile top displacement during grouting were analyzed, and the grouting effect was tested by elastic wave CT. Then, the vertical static load tests of pile foundation were carried out under post-grouting and non-grouting conditions. The results show that the composite post-grouting at the pile bottom can effectively eliminate the sediment at the pile bottom and form an expansion pile end. The bearing capacity of the pile foundation is increased by 34.1%. The pile end resistance enhancement coefficient is 1.70, and the pile side friction enhancement coefficient is 1.32~1.37 within the influence range of the slurry.
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