Time-dependent load-deformation behaviour of foundations under alternating loads in overconsolidated clay

• Applicant: Professor Dr.-Ing. Oliver Reul
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 457580302

In the context of the modernisation and revitalisation of existing buildings, increasingly complex tasks such as the re-use of foundations, have to be addressed, especially in urban areas. An accurate prediction of the load-settlement behaviour of existing foundations is of particular importance if existing and new foundations are to be combined. In order to be able to exploit further optimisation potential by coupling existing foundations with new structures, the time-dependent deformation behaviour of foundations must therefore also be taken into account to a greater extent. This poses high demands on the modelling of the subsoil, since for cohesive soils both consolidation processes and the time-dependent material behaviour (creep) need to be realistically assessed.In addition to the time-dependent deformation behaviour of the soil and changing structural loads arising from demolition and reconstruction phases, construction works in the vicinity also influence the long-term deformation behaviour of foundations. In particular, neighbouring groundwater lower-ings and the associated changes in the groundwater level are responsible for the fact that foundations in urban areas are exposed to alternating loads resulting from changes in uplift and effective stresses in the soil.The focus of the proposed research project will be on the long-term deformation behaviour of raft foundations and piled rafts in overconsolidated clay, with measurements on foundations in Frankfurt am Main extending over several decades to be employed. In addition, centrifuge model tests and coupled pore pressure-displacement finite element analysis are planned, with the time-dependent material behaviour of the soil being represented using visco-hypoplastic material models. It is the aim of this project to investigate the load-bearing behaviour of foundations subjected to alternating loads and to qualitatively and quantitatively assess the effects on the long-term behaviour considering consolidation and creep.In detail, the following topics are to be addressed:- How do alternating loads affect the creep deformations of foundations.- To what extent do creep deformations influence the foundation stiffness during subsequent load-ing phases.- Do raft foundations and piled rafts show different time-settlement behaviour- How do alternating loads, consolidation and creep affect the load distribution between piles and rafts in the case of piled rafts.- How do alternating loads, consolidation and creep affect the design parameters commonly used in engineering practice, namely modulus of subgrade reaction and equivalent pile spring stiffness.

• DFG Programme: Research Grants