Full-scale load testing of two large-diameter drilled shafts in coral-reef limestone formations

Field load tests were conducted on two large-diameter drilled shafts in coral-reef limestone formations in the Male-Airport Island Cross-sea Bridge area in the Maldives. Due to the porosity of the rock mass, the degree of heterogeneity of the cementation, and the particle fragility of the coral-reef limestone in this area, the process of drilling a shaft weakens the side resistance and tip resistance of the shaft; thus, post-grouting was applied to strengthen the weakest zones of the natural coral. This paper presents the results of bi-direction O-cell testing on one 3.2 m diameter and one 1.5 m diameter drilled shaft before and after grouting in coral-reef limestone formations. Comparing with test results before and after grouting shows that the grouting enhanced both the shaft and tip resistance. The two test shafts had higher bearing capacity after grouting, and both of these values met the requirements of the shaft design. Additionally, post-grouting can be applied to coral-reef limestone formations and can effectively improve the bearing capacities of shafts and decrease their settlements. Finally, the research results were directly applied to the design of a bridge foundation and may be applicable to similar projects in coral-reef limestone formations.