Long-Term Behaviour of Floating Pile Foundations in Soft Gothenburg Clay - Advanced Numerical Modelling of Creep Settlements and Soil Pile Interaction

Abstract

Urban development in the city of Gothenburg has become increasingly dependent on complex geotechnical solutions thus the high extent of deep deposits of soft clay and the ongoing densification of the urban environment. In areas subjected to long-term creep settlements, the utilisation of floating piles have become significant. Reliable predictions is therefore essential for safe foundation design.

The aim of the study was to evaluate the long-term behaviour of floating pile found ations in deep deposits of soft clay subjected to creep settlements and asses how these effects can be represented in advanced numerical analyses. The study focused on the area of Lilla Bommen in Gothenburg and was carried out in collaboration with Skanska.

Finite element analyses were carried out using both two-dimensional and three dimensional numerical models in Plaxis. The Creep-SCLAY1S constitutive model was utilised to simulate long-term consolidation and especially creep behaviour of the clay. The numerical results were later compared to measurements of settlements and axial force observed in instrumented piles. Additional investigations were also carried out on the influence of pile spacing and pile length.

The numerical results were compared with the measured settlement data and ob served axial forces. It was shown that the numerical model was able to capture long-term settlement behaviour and partially the development of negative skin fric tion within the floating pile system. However, differences between measured and simulated axial force distribution indicated that the simplified numerical approach may not fully capture realistic pile-group interactions effects and time-dependent load redistribution.

The additional investigations on the influence of pile spacing and pile lengths made it possible to conclude that it has high affect on both settlement behaviour and axial load distribution. Smaller spacing resulted in increased settlements and reduced pile efficiency due to pile group effects. On the other hand, the increasing pile length showed to reduce settlements. Furthermore, substantial differences were observed in the comparison between 2D and 3D analyses, particularly load distribution and the behaviour of edge piles and their effect on piles closer to the centre.

To conclude, the study demonstrates that a simplified 2D unit cell are able to rep resent the average behaviour of centrally located piles which can provide valuable support during design phases. However, the results further indicate that advanced 3D analyses are needed for to capture local effects, edge pile behaviour and load distribution within pile groups subjected to long-term consolidation and creep set tlements. Additionally, the findings highlight the importance of creep deformation in the long-term behaviour of floating piles foundations in Scandinavian soft clay.