Experimental study on the fundamental properties of coral-reef limestone and the vertical bearing behavior of post-grouted rock-socketed shafts

The development of reclaimed islands and reefs has emerged as an important strategic measure for coastal nations. This paper systematically investigates the mechanical properties and engineering characteristics of coral-reef limestone in the proposed area for Male-Airport Island cross-sea bridge project. Based on the results of static load tests and core drilling conducted on post-grouted rock-socketed drilled shafts，this study provides a comprehensive analysis of the bearing deformation characteristics of the shaft embedded in coral-reef limestone before and after grouting. Additionally，the integrity of the shaft and the permeation diffusion range of the grouting are thoroughly evaluated. The test results reveal that the coral-reef limestone exhibits notable characteristics，including low density，large pore sizes，unique structure，strength anisotropy，and uneven cementation. Furthermore，large-diameter post-grouted rock-socketed drilled shafts demonstrate promising application potential in the coral-reef limestone strata. The post-grouting technique enhances the bearing deformation capacity of shaft foundations in coral-reef limestone，with the ultimate bearing capacity of the test shaft increasing by 3.6% after grouting，and the displacement of the shaft head decreasing by 33.53% compared to before grouting. Core drilling tests indicate that the grouting at the shaft tip penetrates approximately 3 m(around 2<italic>D</italic>) downward，which significantly improves the pore structure of the coral-reef limestone. Finally，by correlating the unconfined compressive strength of intact coral-reef limestone with the ultimate side resistance and tip resistance，this paper develops a computational method for calculating the load capacity of grouted rock-socketed drilled shafts in coral-reef limestone formations. This methodology offers a robust scientific foundation and theoretical basis to guide subsequent engineering applications.