# Evaluation of Methods Based on CPTu Testing for Prediction of the Bearing Capacity of CFA Piles
## 4 Discussion  
Before a conclusion can be drawn, some remarks must be mentioned. Pile load tests were performed on the piles manufactured by the same technology and were located in a homogenous geological environment. However, some variation in the fluvial deposit influenced the test output, but this variation was to some extent reflected by the prediction methods.  
Generally, it can be stated that the investigated methods have certain limitations.  
In case of the UniCone method, there is no consideration of pile manufacturing technology for pile tip coefficient, only pile diameter is taken into account.  
The LCPC method shows higher values of predicted bearing capacity in comparison with the measured data. The influence zone around the pile tip is restricted to the interval  
Figure 10: Statistical analysis of prediction methods: (**a**) Probability density function for particular prediction method; (**b**) cumulative probability chart for particular prediction method.  
1.5 pile diameter above and below the pile tip. However, if a less bearable soil is located below this zone, it is not taken into account by this method. The method considers the statistical processing of the measured data from the CPT test using \"curve smoothing\". The measured data, which were not subjected to curve smoothing to obtain a representative cone resistance value \(q_{c,eq}\) for the pile tip, did not cause a significant difference in the results. The difference represented a maximum of \(\pm\)2% of the bearing capacity of the pile tip.  
[PERSON] stated the difference between results of UniCone and LCPC methods as 19% [65]. [PERSON] and [PERSON] designated the LCPC method as most conservative as removing the upper bearing capacity limits leads to the results closer to the measured ones [66]. [PERSON] and [PERSON] noted that more consistent results were achieved for soils with cone penetration resistance from 5 to 15 MPa. In the case of the UniCone method, utilization of the upper limits of pile resistance can be evaluated [2]. Generally, these results are in agreement with the outputs of this study depending on the evaluation criterion.  
The EC 7--2 method based on the Dutch NEN standard shows the worst applicability at given boundary conditions. The approach to obtain the representative \(q_{c}\) value is based on graphical evaluation using \"the path of least resistance\" which is not a convenient method when using computer calculation. The analysis shows inverted distribution of bearing capacity between pile tip and shaft in comparison with other methods. A significant part of the overall bearing capacity comes from the pile tip. [PERSON] and Cadogan or Huybrechts proved the opposite phenomenon when major parts of pile resistance is based on the shaft friction as was verified by other prediction methods [67; 68].  
Pile load tests proved the major contribution of shaft friction of CFA piles to overall bearing capacity. However, pile tip position affects the load/settlement response of the pile in a certain way because of the deformation resistance of soil within the influence zone of the pile tip and disturbance of the soil during drilling of the CFA pile.