Abstract: The investigation on the bearing behavior of pile foundation in coral-reef limestone formation is a hot issue in the geotechnical engineering. Based on the field static loading test of tip post-grouting pile in coral reef limestone formations in the project of a cross-sea bridge, this work analyzed the test results of the trial pile before and after grouting, and the influences of the preloading effect of post-grouting at the pile tip on the pile resistance. The mechanism of improvement for the grouted pile was further studied by the analysis of test results of post-grouting at the pile tip. The results show that the post-grouting technique can be applied to the coral-reef limestone formations, which can effectively improve the bearing capacity of pile foundation and decrease the settlement. Coring test reveals the distribution of pressurized grout, and verifies that the pore of coral-reef limestone is filled by the pressurized grout. The negative side friction is mobilized before application of vertical load because of the negative side friction arising from grout pressure after tip grouting. Thus, the side friction of grouted pile increases. Additionally, the preloading effect of post-grouting at the pile tip enhances the tip resistance and reduces the tip displacement. Consequently, the bearing behavior of pile foundation is improved by post-grouting at the pile tip.

Key words: coral-reef limestone, post-grouting at pile tip, self-balanced method, borehole coring test, preloading effect, pile resistance