Validation of constitutive models for clay for multidimensional cyclic loading

• Applicants: Professor Dr.-Ing. Hans Henning Stutz; Professorin Dr.-Ing. Merita Tafili; Professor Dr.-Ing. Torsten Wichtmann
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 582004673

A high-cyclic loading, characterized by a large number of cycles and small strain amplitudes, can lead to an accumulation of permanent deformations in the soil and therefore endanger the serviceability of foundations or other geotechnical structures. In many cases the stress and strain paths in the soil caused by the high-cyclic loading are multidimensional, for example in case of traffic due to the moving loads, or at foundations of offshore wind turbines as a result of differences in direction and phase between wind and wave loading. From tests on sand it is known that a multi-dimensional cyclic loading leads to a larger accumulation of deformation than a one-dimensional cyclic loading. Nevertheless, most element and model tests in the literature were performed with a one-dimensional cyclic loading only. Likewise, the majority of models for the prediction of long-term deformations have been formulated for a one-dimensional high-cyclic loading. In contrast, the high-cycle accumulation (HCA) model for sand developed in Bochum and Karlsruhe uses a special definition of a multidimensional strain amplitude which is able to capture also multidimensional strain paths. For sand this definition has been already experimentally validated for one- to four-dimensional strain paths. In that context it has been demonstrated that the HCA model with this definition of the strain amplitude is able to accurately describe the accumulation rates under multidimensional high-cyclic loading. The amplitude definition was recently overtaken into the newly proposed HCA model for clay, but a respective validation is still missing. The main objective of the proposed research project is thus the experimental validation of the high-cycle accumulation model for clay, in particular its amplitude definition, for multidimensional loading. The experimental program comprises cyclic triaxial tests, cyclic simple shear tests and cyclic hollow cylinder triaxial tests with one- to four-dimensional stress or strain paths, covering a large spectrum of different paths which puts the validation on a broad basis. Furthermore, the collected experimental data will be used to check the prediction quality of selected implicit constitutive models for clay with respect to multidimensional cyclic loading, and to further develop the constitutive equations of two of these models. These conventional constitutive models are applied for the implicit steps of numerical calculations with the HCA model. During these steps the strain path is recorded, forming the base for the determination of the strain amplitude being an important input parameter of the HCA model.

• DFG Programme: Research Grants