# 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 Tip Grouting Conditions  
In order to analyze the effect of different grouting thickness at the pile tip on the performance of the pile, grouting thicknesses of 0.2 m, 0.5 m, 0.7 m, and 1.0 m were selected for the calculations. The pile segment is calculated as before, with the cement soil consolidation body at the tip of the pile as the 19 th pile segment unit, and the load transfer parameters between the composite pile and the soil after grouting are still taken (Tables 1 and 2). Calculations were carried out based on the iterative method described in Section 1, and the load settlement relationships for the pile at different grouting thickness obtained from the results are shown in Figure 5.  
It can be seen from Figure 5 that the ultimate load capacity of the pile is increased after the pile tip grouting and the settlement at the top of the pile also increases, and increases with the increase of the grouting thickness.  
The ultimate pile top load and the corresponding values of the total pile side frictional resistance and total pile tip resistance for different grouting thickness are calculated, and the relationship between the three and the pile tip grouting thickness is shown in Figure 6.  
As can be seen from Figure 6, the increase in pile load capacity is mainly due to the increase in pile tip resistance, while the increase in pile side frictional resistance is very limited. This is due to the fact that the slurry spreads under pressure into the soil layer at the tip of the pile, creating an enlarged head that increases the cross-sectional area at the bottom of the pile with very limited increase in the side area of the pile. The pile tip resistance is thus increased and the pile side frictional resistance is only slightly increased, while with the increase in grouting thickness the cross-sectional area at the bottom of the pile no longer increases and the total pile side area continues to increase, so the pile tip resistance no longer increases and the pile side frictional resistance increases, but only to a very limited extent. From the results, it appears that the pile tip grouting mainly improves the pile tip resistance and has less effect on the pile side resistance.  
Figure 5: Load settlement relationship for pile with different grouting thickness.  
In order to prevent the cement soil consolidation body at the tip of the pile from punch failure [16] and considering the feasibility of practical construction, this paper suggests that the thickness of the pile tip grouting be taken as 0.5 m. Under this condition, the ultimate bearing capacity of the pile after grouting was increased from 1854 kN to 2207 kN, an increase of 19%, the total pile tip resistance was 295 kN and 577 kN before and after grouting, respectively, an increase of 96%, and the total pile side frictional resistance was 1560 kN and 1630 kN before and after grouting, respectively, an increase of only 4%, It is shown that the main thing that pile tip grouting improves is the pile tip resistance. If this grouting thickness is used for pile tip grouting, the total number of piles required can be reduced from 192 to 162 with the same total bearing capacity.  
As can be seen from Figure 5, the settlement at the top of the pile corresponding to the ultimate load of the pile is 15.3 mm when the pile is ungrouted, and the settlement corresponding to the ultimate load of the pile increases as the grouting thickness increases. Settlement increased to 17.3 mm at a grouting thickness of 0.5 m, mainly due to increased settlement at the top of the pile caused by the compression of the grouting segment. If we consider that the settlement at the top of the pile is still controlled at 15.3 mm, the vertical bearing capacity of the pile with a slurry thickness of 0.5 m at the tip of the pile is 2127 kN, an increase of 14%. The total number of piles required can be reduced from 192 to 169 while ensuring the total bearing capacity remains unchanged.