# Study on Vertical Load-Carrying Capacity of Post-Grouting Bored Piles
## 4 Effect of Grouting on the Performance of Bored Pile
### Calculation of Vertical Ultimate Load under Pile Side Grouting Conditions  
To analyze the effect of different grouting length ratio on the pile side on the performance of the pile, the grouting length was increased sequentially from bottom to top according to the pile segmentation, defining the grouting length ratio \(n\) as follows  
\[n=\frac{L_{0}}{L} \tag{17}\]  
where \(L_{0}\) is the length of the grouting segment and \(L\) is the pile length.  
The pile segmentation is calculated as before, and the parameters for the load transfer between the composite pile and the soil after grouting are still taken according to Tables 1 and 2. The calculations were carried out according to the iterative method described in Section 1, and based on the results the load settlement relationships for the pile with different grouting length ratio are shown in Figure 7.  
Figure 6: Relationship between \(P_{0}\), \(Q_{\mathrm{s}}\), \(Q_{\mathrm{b}}\) and grouting thickness.  
As can be seen in Figure 7, the ultimate load of the bored pile is increased after the pile side grouting and increases with the increase of the grouting length ratio. Increase in the pile axial force resulted in an increase in the pile compression and therefore in increased settlement of the pile top corresponding to the ultimate pile load capacity, which increased to 17.2 mm after full-length grouting.  
To calculate the ultimate pile top load and the corresponding total pile side frictional resistance and total pile tip resistance for different grouting length ratio, the relationship between the three and the pile side grouting length ratio is shown in Figure 8.  
From Figure 8, it can be seen that the ultimate bearing capacity of the pile is significantly increased after grouting. With the increase in the grouting length ratio, the ultimate bearing capacity of the pile also increases, and the increase of the ultimate bearing capacity of the pile is related to the increase of both the pile tip resistance and the pile side frictional  
Figure 8: Relationship between \(P_{0}\), \(Q_{s}\), \(Q_{b}\) and grouting length ratio.  
Figure 7: Load settlement relationship of pile under different grouting length ratio.  
resistance. This is because the pile side grouting is done from the bottom up, so that the pile side area is slightly increased and the pile bottom cross-sectional area is increased after grouting. This results in a significant increase in pile tip resistance and only a slight increase in pile side frictional resistance. As the grouting length ratio increases the cross-sectional area at the bottom of the pile stops increasing and the total area on the side of the pile continues to increase, so the resistance at the tip of the pile stops increasing and the frictional resistance on the side of the pile continues to increase.  
The ultimate pile load was increased from 1854 kN to 2761 kN after full-length pile side grouting, an increase of 49%. The total pile side frictional resistance was 1560 kN and 2184 kN before and after grouting, an increase of 40%, and the total pile tip resistance was 295 kN and 577 kN before and after grouting, an increase of 96%, indicating that pile side grouting has increased both pile side frictional resistance and pile tip resistance. If full-length pile side grouting is used, the total number of piles required can be reduced from 192 to 129, while ensuring that the total bearing capacity remains unchanged.  
According to the analysis in Figure 7, if we consider that the settlement at the top of the pile is still controlled at 15.3 mm of the ungrouted pile, the bearing capacity of the pile after grouting the full length of the pile side is 2674 kN, which is an increase of 44%. The total number of piles required can be reduced from 192 to 134, while ensuring that the total bearing capacity remains unchanged.