# Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand
## 6 Conclusions  
This paper presents a model test of an axially loaded single pile in a calcareous sand foundation. The axial bearing behavior of single piles, with and without post-grouting, in calcareous sand are studied, and the test results are compared with those of single piles, with and without post-grouting, in siliceous sand. The distribution of the cement-stabilized mass and the bearing mechanism of grouted piles are analyzed by considering the excavation observation of grouted single piles. Based on the analyses and discussions of this study, the following conclusions can be reached:  
1. The change in shaft resistance, caused by the lateral extrusion of calcareous sand during pile driving, is less than the negative effect caused by particle breakage; therefore, the response of an ungrouted pile subjected to axial load in calcareous sand is lower than that in siliceous sand. After grouting, the axial bearing capacity of a single pile is greatly improved in both model foundations, and the calcareous sand formation is significantly enhanced by the injected cement grout; hence, the grouted single pile shows basically identical bearing behavior in the two types of sandy soil formations. In addition, compared with annular point grouting, ideal-geometry grouting has more obvious advantages in improving the bearing characteristics of pile foundations and shows higher stability in improving the bearing properties of pile foundations. 2. Post-grouting has affects the load transfer responses of the pile. Given that grouting at the side of the pile increases the effective horizontal stress of the soil around the pile, the enhanced shear strength of the soil can effectively offset the transmission of the axial force of the pile, resulting in the load attenuation of the grouted pile along the depth direction is faster than that of the ungrouted pile. 3. The particle breakage characteristics of calcareous sand during pile driving will reduce the shaft resistance of the pile, so the ungrouted single piles in calcareous sand has a lower shaft resistance than that in siliceous sand. The grout fills the holes and pores on the surface of calcareous sand and enhances the surrounding soil by the solidification effect of injected cement grout, which forms a new structural equilibrium state for the pile-soil interaction system and effectively improves the physico-mechanical properties of the surrounding soil. The grouted pile has a higher shaft resistance than the ungrouted pile, and the increased ratio of the total shaft resistance after grouting in calcareous sand formations is better than that of piles in siliceous sand formations. 4. Grouting at the side of the pile can not only improve the strength of the surrounding soil but also increase the strength of the bearing layer at the pile tip so that the single pile without post-grouting has a lower tip resistance than that of the single pile with post-grouting. This result indicates that the mobilization of the tip resistance can be enhanced by the soil improvement at the pile side due to side grouting. 5. The analysis of the static load test and excavation observations shows that the annular point grouting does not have an obvious reinforcement effect due to the uncertainty of the grouting flow direction, which results in a large discreteness of the increase in bearing capacity after grouting. The use of an ideal-geometry grouting device can effectively control the key parameters, such as the grouting amount and grouting pressure, so it can form an ideal geometric shape, which standardizes the application of the post-grouting technique. 6. The analysis of the bearing mechanism of the post-side-grouted pile shows that, compared with the annular point grouted pile, the ideal-geometry grouted pile forms a larger bonding surface between the cement-stabilized mass and the pile shaft, which forms a more stable pile-soil interaction structure system.