# Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand
## 5 Discussion  
The test results have proven that the post-grouting technique can increase the bearing capacity of a pile in calcareous sand by enhancing the shaft resistance and tip resistance, and calcareous sand formations can be effectively improved by injected cement grout. Table 3 shows the measured ultimate bearing capacity of each single pile, the corresponding measured values of the total shaft resistance, tip resistance, and their increase range. The table shows that, under the ultimate load, the load sharing of tip resistance is relatively small, which indicates that the single pile is mainly borne by the shaft resistance during the process of axial loading and the pile head load is mostly supported by the shaft resistance under the ultimate load. The total shaft resistance of annular point grouted piles MP2 and MP5 increases by 175.26-492.93%, and the tip resistance increases by 33.12-267.14%. The total shaft resistance of ideal-geometry grouted piles MP3 and MP6 increases in the range of 301.34-338.95%, and the tip resistance increases by 87.26-130.00%. The test results show that side grouting significantly improves the shaft and tip resistances of the pile foundation. It is also evident that the total shaft resistance and tip resistance of annular point grouted piles are more discrete than those of ideal-geometry grouted piles. Directional flow grouting can effectively increase the response of the axially loaded pile. In addition, the tip resistance of piles with post-grouting is improved compared with piles without post-grouting, which indicates that grouting at the side of the pile can not only enhance the strength of the soil at the side of the pile but also improve the strength of the bearing layer at the end of the pile. This conclusion is consistent with the conclusion, given by [PERSON] et al. [28], that the mobilization of the tip resistance can be enhanced by the soil improvement at the pile side, due to side grouting. As mentioned above, the increase in post-grouting on the bearing capacity of piles in calcareous sand is better than that of piles in siliceous sand. Simultaneously, in Table 3, the post-grouted pile in calcareous sand also has better increased ratio of total shaft resistance than that in siliceous sand, which further indicates that the injected cement grout fills the concave and convex holes on the surface of calcareous sand, enhances the interface meshing between calcareous sand particles and cement grout, and effectively improves the interface structure performance. The results are consistent with the conclusion, reported by [PERSON] et al. [29], that cement stabilized calcareous sand has higher integral strength than cement stabilized siliceous sand using microscopic test methods. Through the abovementioned analysis, the bearing capacity of an annular point grouted pile increases discretely, due to the uncertainty of the grout flow direction and the formation of an irregular cement-stabilized mass during the grouting process. Directional flow grouting can form an ideal geometric shape and can effectively control the amount of grouting, and reduce the uncertain factors in the grouting process, to achieve the expected