Experimental investigation and constitutive modeling of the behaviour of soils with organic content under low- and high-cycle loading

• Applicants: Dr.-Ing. Meisam Goudarzy; Professor Dr.-Ing. Frank Rackwitz; Professor Dr.-Ing. Torsten Wichtmann
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 528532847

The continuous expansion of urban areas and the development of transportation infrastructure increasingly necessitates the construction of buildings, highways or railway tracks on problematic ground. Organic soils like peat have long been recognized as problematic ground, primarily due to their high compressibility and pronounced creep. In case of transportation infrastructure, the traffic due to trains or trucks causes a high-cycle loading of the subsoil. Such loading with a large number of cycles may lead to an accumulation of permanent settlements, potentially endangering the serviceability of the structure. Consequently, the long-term deformations caused by the high-cycle loading should be predicted and considered in the design. A low-cycle loading, characterized by a low number of cycles with potentially large amplitudes, can result from seismic events, which may be of endogenic (e.g. due to plate tectonics) or anthropogenic origin. For example, earthquakes induced by natural gas production are a common source of ground vibration in peat deposits in The Netherlands. Risk assessment analyses of such earthquakes necessitate a deep knowledge of the behaviour of soils with organic content under low-cycle loading. This includes the stiffness and damping properties of the soils at small to intermediate strain amplitudes, as well as the possible excess pore pressure build-up at larger amplitudes. Despite its practical relevance, the available knowledge on the behaviour of soils with organic content under both low-cycle and high-cycle loading is limited. Only few experimental studies have addressed these issues, and they were restricted to site-specific soils and a limited number of influencing parameters. Furthermore, the few proposed constitutive models fail in describing the complex behaviour of soils with organic content under low- and high-cycle loading. Therefore, a thorough experimental investigation on a soil with organic content including monotonic, cyclic and dynamic loading and the development of constitutive equations for low- and high-cycle loading are the main purposes of the research project. For the sake of reproducibility, the experiments will be performed on an artificial soil composed of a mineral (kaolin) and an organic component (highly decomposed peat). Homogeneous samples of these mixtures with different organic content are prepared by slurry consolidation and tested in oedometer, triaxial, direct simple shear and resonant column experiments. In these tests several influencing parameters like mean stress, stress amplitude, loading rate or frequency, and loading direction with respect to the predominant fiber orientation are varied. Based on a visco-hypoplastic approach and a high-cycle accumulation model for clay, constitutive models adequately describing the mechanical behaviour of soils with organic content under low- and high-cycle loading will be developed.

• DFG Programme: Research Grants