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

Sammanfattning

Urban development in the city of Gothenburg has become increasingly dependent oncomplex geotechnical solutions thus the high extent of deep deposits of soft clay andthe ongoing densification of the urban environment. In areas subjected to long-termcreep settlements, the utilisation of floating piles have become significant. Reliablepredictions is therefore essential for safe foundation design.The aim of the study was to evaluate the long-term behaviour of floating pile foundations in deep deposits of soft clay subjected to creep settlements and asses howthese effects can be represented in advanced numerical analyses. The study focusedon the area of Lilla Bommen in Gothenburg and was carried out in collaborationwith Skanska.Finite element analyses were carried out using both two-dimensional and threedimensional numerical models in Plaxis. The Creep-SCLAY1S constitutive modelwas utilised to simulate long-term consolidation and especially creep behaviour ofthe clay. The numerical results were later compared to measurements of settlementsand axial force observed in instrumented piles. Additional investigations were alsocarried out on the influence of pile spacing and pile length.The numerical results were compared with the measured settlement data and observed axial forces. It was shown that the numerical model was able to capturelong-term settlement behaviour and partially the development of negative skin friction within the floating pile system. However, differences between measured andsimulated axial force distribution indicated that the simplified numerical approachmay not fully capture realistic pile-group interactions effects and time-dependentload redistribution.The additional investigations on the influence of pile spacing and pile lengths madeit possible to conclude that it has high affect on both settlement behaviour and axialload distribution. Smaller spacing resulted in increased settlements and reduced pileefficiency due to pile group effects. On the other hand, the increasing pile lengthshowed to reduce settlements. Furthermore, substantial differences were observedin the comparison between 2D and 3D analyses, particularly load distribution andthe 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 represent the average behaviour of centrally located piles which can provide valuablesupport during design phases. However, the results further indicate that advanced3D analyses are needed for to capture local effects, edge pile behaviour and loaddistribution within pile groups subjected to long-term consolidation and creep settlements. Additionally, the findings highlight the importance of creep deformationin the long-term behaviour of floating piles foundations in Scandinavian soft clay.