# Evaluation of Methods Based on CPTu Testing for Prediction of the Bearing Capacity of CFA Piles
## 3 Results
### Analysis of Predicted Pile Bearing Capacity  
CPTu probes proved variable thickness of fluvial deposit under bridges SO--201 and SO--202. The consequence of this fact is noticeable during the pile bearing capacity calculation, especially the LCPC method which influences where the zone of pile tip is located within the interval of 1.5 pile diameter above and below pile tip. The difference in the tip bearing capacity of pile No. 2 (fluvial deposit with thickness of 1.6 m) and pile No. 3 (fluvial deposit with thickness of 1.1 m), which end at same level, is 651 kN or 51%. The same phenomenon was observed at piles No. 5 and No. 6 where thickness of more  
Figure 7: CPTu record with geological profile and position of tested pile (gray rectangle). \(h\) is depth in meters; —18.6 m is overall depth of the CPTu probe. bearable fluvial sediments was 1.8 m and 0.9 m, respectively. The difference in tip bearing capacity of pile No. 5 and pile No. 6 is 489 kN or 37.8%. Piles No. 2, 3, 5, and 6 were designed in accordance with the same survey borehole; therefore, the mentioned piles were manufactured with practically identical length and vertical position of the pile in soil stratum (Table 2). \begin{tabular}{c c c c c c c c c} \hline \hline
**Method** & \multicolumn{3}{c}{\(Q_{p}\),**_LinConae_} & \multicolumn{3}{c}{\(Q_{p}\),**_LCPC_} & \multicolumn{3}{c}{\(Q_{p}\),**_EC 7\(-\)2_} \\ \hline
**Pile No.** & \(Q_{s}\) & \(Q_{b}\) & \(Q_{p}\) & \(Q_{s}\) & \(Q_{b}\) & \(Q_{p}\) & \(Q_{s}\) & \(Q_{b}\) & \(Q_{p}\) \\  & **(kN)** & **(kN)** & **(kN)** & **(kN)** & **(kN)** & **(kN)** & **(kN)** & **(kN)** & **(kN)** \\ \hline
1 & 1665 & 671 & 2336 & 1059 & 894 & 1953 & 116 & 1650 & 1766 \\
2 & 2016 & 859 & 2875 & 1346 & 1274 & 2621 & 339 & 1177 & 1516 \\
3 & 1967 & 753 & 2721 & 1084 & 623 & 1707 & 169 & 1375 & 1545 \\
4 & 1856 & 671 & 2527 & 1031 & 516 & 1547 & 129 & 1297 & 1426 \\
5 & 1671 & 817 & 2488 & 1256 & 1292 & 2548 & 26 & 1720 & 1746 \\
6 & 1783 & 671 & 2453 & 1021 & 803 & 1824 & 125 & 1821 & 1946 \\
7 & 1330 & 849 & 2179 & 653 & 1294 & 1947 & 262 & 1836 & 2098 \\
8 & 760 & 897 & 1657 & 573 & 2170 & 2743 & 28 & 3982 & 4000 \\
9 & 1338 & 1052 & 2390 & 767 & 1528 & 2295 & 48 & 3131 & 3180 \\ \hline \hline \end{tabular}   
Notes: \(Q_{s}\): pile shaft bearing capacity; \(Q_{b}\): pile tip bearing capacity; \(Q_{p}\): overall pile bearing capacity. Loose fluvial sediments were identified during CPTu sounding and their occurrence is also mentioned in documentation of geological survey [29]. Variability of thickness of fluvial deposit has no significant influence on pile tip bearing capacity according to UniCone and EC 7--2 methods. Piles under bridges SO--201 and SO--202 and pile No. 7 show lower bearing capacity according to LCPC method by 16 to 39% in comparison with the UniCone method. Only bearing capacity of pile No. 5 is higher by 2%. The same tendency was observed with the EC 7--2 method where bearing capacity is lower by 4 to 47% in comparison with the UniCone method. Gravel fraction is more present in fluvial sediments under bridges SO--203 and SO--204 with thickness of 1.7 to 1.9 m. This was proved by higher values of cone penetration resistance \(q_{c}\) in lower a part of the formation. Together with higher thickness of this deposit led to higher bearing capacity calculated by the LCPC and EC 7--2 methods in comparison with the UniCone results. On the other hand, UniCone output was not significantly affected by this phenomenon. The significant difference in bearing capacity was observed between LCPC and EC 7--2 methods at pile No. 2 with 42% higher value with LCPC method. Another significant difference was identified at pile No. 8 where the LCPC method shows lower bearing capacity by 46% in comparison with the EC 7--2 method (Table 3). Comparing LCPC and EC 7--2 methods, the overall trend is similar but it should be mentioned that the EC 7--2 method puts more than 70% of overall bearing capacity to the pile tip at every calculated pile.