# Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand
###### Abstract  
Post-grounded piles, as a foundation form for large-span and large-scale structures on calcareous sand, are expected to provide a high bearing capacity, but research on the response of post-grounded piles subjected to axial load in calcareous sand is still in the exploratory stage. In this paper, a model test is constructed for static pressure piles in calcareous sand under axial loading. The response of axial compressive piles, with and without post-grouting, in calcareous sand were investigated, and the test results were compared with those of axial compressive piles, with and without post-grouting, in siliceous sand. The influence of post-side-grouting on the response of a single pile subjected to axial compressive load in calcareous sand and its bearing mechanism were further analyzed. The results show that the change in shaft resistance, caused by the lateral extrusion of calcareous sand, is less than the negative effect caused by particle breakage during pile driving, so single piles without post-grouting in calcareous sand exhibit weaker axial bearing behavior than that in siliceous sand. A single pile with post-side-grouting in calcareous sand can provide a higher bearing capacity by increasing the shaft resistance and tip resistance compared with a single pile without post-side-grouting, and the increased ratio of the bearing capacity of piles, after footing in calcareous sand, is better than that of piles in siliceous sand. Post-side-grouting can not only strengthen the surrounding soil by the solidification effect of injected cement grout, but it can also have a strengthening effect on the tip resistance. In addition, ideal-geometry grouting has more obvious advantages in improving the bearing behavior of pile foundations than annular point grouting, and higher stability in improving the bearing properties of pile foundations is evident for ideal-geometry grouting. Therefore, it is suggested that a directional grouting device should be adopted in actual projects in the future to form a more stable pile-soil interaction system and to expand the application prospect of pile foundations in calcareous sand. c 2022 2022 22 March 2022 2  
bearing behavior of pile foundations in calcareous sand mainly focuses on in situ tests and indoor model tests. [PERSON] et al. [6] presented field load tests on driven piles in calcareous sand of the Bass Strait, and the results showed that the average ultimate shaft resistance was approximately 13 kPa, and its bearing capacity was only 20% of the empirically predicted value of the driven pile in quartz sand. [PERSON] and [PERSON] [7] analyzed a series of pull-out tests of driven piles in calcareous sand of the Gulf of Suez, and they provided a recommended value of 15 kPa for the ultimate shaft resistance and explained the reasons for the low bearing capacity of driven piles in calcareous sand. [PERSON] et al. [8] performed a series of static load tests on calcareous sand at the North Rankin A site, revealed the shaft resistance and deformation characteristics of piles, and found that the peak value of shaft resistance decreased with increasing burial depth. [PERSON] et al. [9] also performed a static load test on jacked piles at the North Rankin A site and obtained the same conclusion as that given above. The peak value of the shaft resistance does not increase with increasing burial depth. [PERSON] et al. [10] studied the response of large-diameter driven piles in coral reefs, based on a high-strain dynamic detection method, and found that the unit shaft resistance of calcareous sand in the upper soil layer of the pile shaft was only 10 kPa, which further indicated that the shaft resistance of the driven piles was small. [PERSON] and [PERSON] [11] obtained the shaft resistance of piles in calcareous sand and quartz sand under different piling methods, through indoor model tests, and showed that the pile in calcareous sand had a much smaller shaft resistance than that in quartz sand.