Prediction of Pile Shaft Capacity in Tension Based on Some Direct CPT Methods—Vistula Marshland Test Site

Abstract

This paper presents different CPT methodologies for the prediction of the pile shaft resistance in tension on the example of three reference screw piles of the Jazowa test site in Poland. The shaft capacity was estimated based on the cone resistance, sleeve friction and CPT excess pore water pressure. Three piles with a diameter of 0.4 m and the length varied from 8 m to 14.6 m were subjected to static load tests in tension. Their results were used to determine the ultimate bearing capacity of the reference piles. The pile shaft resistance was estimated according to the AFNOR standard, Doan and Lehane 2018 centrifuge tests based method (Delft University of Technology approach), the Modified Unicone method, KTRI (Kajima Technical Research Institute) and LCPC (Laboratoire Central des Ponts et Chaussées) method. Then, the ultimate bearing capacity determined in static load tests was compared to the estimated values according to five different methods. The best estimation, fitting almost perfectly to static load test values, was obtained with the AFNOR method, whereas the other predictions significantly underestimated the ultimate bearing capacity.

Statistical Evaluation of Sleeve Friction to Cone Resistance Ratio in Coarse-Grained Soils

“…Although it is hardly possible to accurately determine the granulometric composition of soil using this particular testing method, fairly clear differences in soil behaviour can be found. Cone resistance (q c ) is higher in sand than in clay of the same strength, and the ratio of f s to q c is lower in sand than in clay [4].…”

“…Both soil classification and the calculation of the bearing capacity of pile foundations clearly show that the friction ratio of cone resistance reflects the type of soil behaviour, considering the evaluation of its type in consonance with its granulometric composition [3,4].…”

“…This study aimed to analyse data obtained using the CPT on coarse soils and to examine the possibility of dividing similar soils into smaller groups (for example, fine sand, medium sand and gravel), considering their friction to cone resistance ratios. The introduced classification of soil is important from a practical point of view for solving design tasks [4,13,14]. Regulatory documents do not provide the above classification, although it significantly affects the results of design tasks.…”