Pile groups under cyclic horizontal loading

• Applicant: Professor Dr.-Ing. Oliver Reul
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321719367

According to EA-Pfähle (EA-P) (DGGT 2012) cyclic loading is defined as a repetitive loading of piles where forces of inertia acting on the pile-soil-system do not need to be considered. Cyclic loading of pile foundations is of importance in various fields of civil engineering such as offshore- and onshore- wind turbines or structures for transport infrastructure. For offshore wind turbines mainly monopiles (i.e. single piles with large diameters) or jacket-structures with large pile spacing (i.e. interactions between piles are of minor importance) are constructed. However, bridge abutments are frequently founded on groups of piles with relatively small pile spacing. Foundations of this type comprising a number of interacting piles subsequently will be termed pile groups. Cyclic loadings are caused for example by wind and waves (offshore wind turbines) or temperature induced constraints (integral bridges without joints and bearings).According to EA-P there is only limited knowledge available for piles under cyclic loading. To consider cyclic temperature induced constraints for integral and semi-integral bridges, frequently more or less arbitrarily chosen reduction coefficients are applied in the design process. It is therefore the main objective of the project to carry out a fundamental study on the bearing behaviour of pile groups under cyclic horizontal loading and to evaluate the results qualitatively as well as quantitatively. Within this study the influence of parameters such as subsoil conditions, pile group geometry and loading condition are to be investigated experimentally and numerically. Pile group geometries and loading conditions are to be based on configurations typical for integral and semi-integral bridges.In detail the following topics are to be treated:- Identification of the main parameters influencing the bearing behaviour of pile groups under cyclic horizontal loading.- Review of the reduction coefficients documented in the EA-P for the distribution of pile loads and Winkler modulus within a pile group under static loading and adjustment of these coefficients for significant cyclic loading.- Development of an analysis model based on the Enhanced Strain Wedge Model (ESWM) by Tasan (2011) which allows the determination of the following parameters: + Accumulation of the horizontal displacement at the pile head. + Distribution of the Winkler modulus along the pile shaft for the various piles within the pile group. + Distribution of bending moment and shear force along the pile shaft for the various piles within the pile group.

• DFG Programme: Research Grants