# Evaluation of Methods Based on CPTu Testing for Prediction of the Bearing Capacity of CFA Piles
## 5 Conclusions  
An evaluation procedure was adopted to investigate the ability of the prediction methods to determine the bearing capacity of the pile in accordance with the results of the static load tests. CFA piles were situated in loess and the tip in fluvial sediments. Four different criteria were selected for the evaluation scheme. Each criterion was used to rank the methods based on their effectiveness or performance. The results of the study indicate that the UniCone method is most applicable for the investigated set of CFA piles and geological conditions. The method presented in the EC 7--2 standard showed the highest variability of results, and we do not recommend its application for similar geological conditions with the given pile manufacturing technology without a deeper analysis.  
Despite an extensive database of piles and geological conditions at the formulation of prediction methods, direct application of any of the investigated methods in practice requires some modification or careful approximation. Two of the prediction methods proved that a major part of bearing capacity of CFA piles comes from shaft friction. Despite the occurrence of loess along the pile body and thin layer of fluvial sediments at the pile tips, piles showed restricted settlement during load tests which complicates the evaluation of loading curve and determination of appropriate pile resistance value representing the pile bearing capacity. This becomes more obvious when certain movement of the pile along the shaft is necessary to fully activate the friction part of the bearing capacity. The influence of the shaft friction increases with increasing pile length and diameter and can be more significant in comparison with the drilled piles according to other studies. However, the contribution of the CFA pile tip to the total pile bearing capacity was proved by the load tests.  
The use of CPT probing in the design of piles requires appropriate interpretation of the test results. The application of any prediction method to specific conditions encountered in design practice requires due attention, especially the interpretation of survey data, the used initial database of experimental measurements, pile manufacturing technology, method limitations, etc. The practical applicability of any of the presented methods cannot be considered final or universal. A particular approach can provide outputs with variable reliability depending on the boundary conditions regardless of supporting database utilized for the development of the method.  
For predictive analysis, it is advisable to use more modern and updated methods that make maximum use of the outputs from CPT sounding and which are developed from a larger database of pile tests. The development of these methods should continue by expanding the database of tested piles together with the application of more advanced rock environment testing procedures, e.g., using seismographs in CPT equipment, Marchetti flat dilatometer, etc. This allows a better understanding of the interaction between the pile foundation and the foundation soil and increase the reliability of the design methods.  
[PERSON] and [PERSON] performed the in situ tests; [PERSON] performed calculations; [PERSON] analyzed test and calculation outputs and wrote the original paper; [PERSON] revised the draft. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Operational Programme Integrated Infrastructure: Application of innovative technologies focused on the interaction of engineering constructions of transport infrastructure and the geological environment, ITMS2014+ code 313011 BWS1. The project is co-funding by European Regional Development Fund.  
Not applicable.  
Due to the nature of this research, participants of this study did not agree for their data to be shared publicly and are only available upon reasonable request.  
The authors declare no conflict of interest.