CT- and multi-monitoring ready thermo-frozen-hydro-mechanical 3D loading system

• Subject Area: Geophysics and Geodesy
• Term: Funded in 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 500412763

In view of the upcoming climate change, the analysis of frozen soil materials is of fundamental importance for the adaptation or mitigation in urban areas as well as for the understanding of occurring geological phenomena. The currently existing permafrost soils are essential in securing the organic carbons encapsulated therein and in stabilizing the existing soil structures, such as constantly and seasonally frozen soils (cryosols) in the cryosphere, embankments, foundations, due to the high rigidity of the subsoil. Here, the basic understanding of changing the coupled cryo-hydro-mechanical soil properties must be improved, so that in addition to the changed chemical, biological processes through the thawing or the transition of the cyclical, alternating thawing / freezing of upper cryosols, the resulting hydraulic, mechanical Changes such as weathering, loss of stiffness and strength, frost-related mixing and erosion can be assessed and modeled. Changes in the cryopedogenic processes such as ice segregation, ice accumulation and cryometamorphosis under alternating thawing / freezing are also unknown.In the adaptation of urban life and the mitigation of increasing urban heat hotspots, the cooling of infrastructures becomes more important. To do this, urban ice stores must be built on a geological scale. Initial research on this is already in progress. From a structural engineering point of view, freezing processes with the load-bearing capacity or protection against failure are known. Cyclical freezing processes, such as those required for the use of ice storages, are completely unknown in terms of their effects. The effects of cyclical freeze-thaw hysteresis on the volumetric pore space and structure changes, in the Atterberg limits or mechanical strength and compressibility degradations have hardly been analyzed and have significant effects on sediments with a larger proportion of fine particles. Secure geomechanical forecasts for these sediments for cyclical freeze-thaw cycles are not yet possible.For the modeling of the cyclic cryo-hydro-mechanical material behavior of frozen soils, a large number of different experimental tests are to be carried out, for which a previously non-existent laboratory device is to be purchased. For the experimental 3D analyzes of the soil samples, a 3-dimensional pressure system for cyclical cryo-thermo-hydro-mechanical loading is to be acquired, which in addition to the cyclical freezing / thawing, the additional installation of further monitoring devices (digital cameras for particle image Velocity, thermography cameras, laser technology, μCT's, radar, etc.) are allowed directly on the sample and during the test process, so that local changes in the structure can be recorded in high resolution as tomography or surface plot and transferred to the modeling.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: CT- und Multi-Monitoring fertiges Thermo-Gefrier-Hydro-Mechanisches 3D Belastungssystem
• Instrumentation Group: 2940 Spezielle Baustoff- und Bodenprüfgeräte, Schergeräte
• Applicant Institution: Christian-Albrechts-Universität zu Kiel
• Leader: Professor Dr.-Ing. Frank Wuttke