Enhancement of load bearing of post-grouted drilled shafts based on in situ tests

Field load tests were conducted for three large-diameter drilled shafts in the flood detention area of the grand bridge project of Beijing–Hangzhou Canal. Bi-directional testing of two grouted drilled shafts (TS1 and TS2) and one ungrouted drilled shaft (TS3) was used to study how post-grouting improved the bearing capacity of the drilled shafts. Based on the test results, the enhanced mechanism of the combined grouted drilled shafts was analyzed, and the analysis of load–displacement response was presented. It shows that grouting can significantly decrease the settlement of the drilled shafts and enhance resistance. By comparing the test results of the grouted and ungrouted shafts, it is found that the mechanical properties of the soil around the shaft can be improved effectively by post-grouting with the pressurized cement grout of the tip and side of the shaft. Furthermore, the effects of preloading on the load transfer characteristics of a shaft are also discussed. It can improve the asynchrony and incongruity between the side resistance and the tip resistance and promote the mobilization of tip resistance. The ratios of the tip resistance to the ultimate bearing capacity of test shafts TS1 and TS2 after post-grouting reached 37.11% and 41.72%, respectively, while the ratio of the ungrouted test shaft TS3 was 23.83%.