# Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand
## 3 Analysis of the Loading Test Results  
### Load-Settlement Response of a Single Pile  
The load-settlement curves can be obtained by the loading test data for the six model piles. The load-settlement responses at the pile head of the six model piles under compression are shown in Figure 4.  
Figure 4 shows that the load-settlement curves of ungrouted piles have obvious inflections, and the load-settlement curves of grouted piles tend to be smoother than those of ungrouted piles. The load-settlement curve of each single pile is relatively gentle and approximately linear during the initial load increments. The settlement of a single pile gradually increases with applied load, and the load-settlement curve of a single pile presents an obvious nonlinearity. For the ungrouted piles, when the ultimate load is reached, the load-settlement curve sharply plunges, which repres  
Figure 4: Load-settlement curves of piles: (**a**) calcareous sand; (**b**) siliceous sand.  
Figure 3: Static load test of a single pile and testing element arrangement (unit: cm): (**a**) front view; (**b**) vertical view.  
of the pile. For grouted piles MP2 and MP6, the bearing capacity of a single pile after grouting has been greatly improved so that it is loaded to the device limit without a distinct inflection. [PERSON] and [PERSON] [23] and [PERSON] et al. [24] proposed that the load prior to failure is determined to be the axial compressive bearing capacity of a single pile, while the maximum test load is taken to be the axial compressive bearing capacity of a single pile in the case of no obvious inflections. Therefore, the ultimate bearing capacities of single piles MP1, MP2 and MP3 are 735 N, 4200 N, and 3080 N, respectively. The ultimate bearing capacities of MP4, MP5 and MP6 are 1200 N, 3080 N, and 4480 N, respectively.  
Figure 4 also shows that MP4 for ungrouped piles has greater bearing capacity than MP1 because the soil around the pile is compacted by lateral extrusion of siliceous sand in the process of pile driving, and the lateral pressure increases. The calcareous sand is subjected to lateral compression and prone to particle breakage, due to its own particularity in the process of pile driving, which leads to the loosening of the soil around the pile, thus reducing the lateral pressure to some extent. The bearing capacity of a single pile is substantially improved after grouting in both siliceous sand and calcareous sand, and calcareous sand formations are effectively improved by injected cement grout; therefore, the single pile exhibits roughly identical bearing capacity in the two types of sand formations. In calcareous sand, the annular point grouted pile MP2 has greater ultimate bearing capacity than the ideal-geometry grouted pile MP3, while the annular point grouted pile MP5 in siliceous sand has a lower ultimate bearing capacity than the ideal-geometry grouted pile MP6, which indicates that annular point grouting promotes substantial discreteness in improving the response of the axial loaded single pile. In addition, the bearing capacities of post-grouted piles in calcareous sand and siliceous sand increase by 457-571% and 257-373%, respectively. The test results show that the post-grouting improves the bearing capacity of piles in calcareous sand better than that of piles in siliceous sand. Because that the surface of calcareous sand is uneven and porous, the injected cement grout fills its holes and pores to form a whole with high strength.