Microscale investigations of the hydro-mechanical behaviour of unsaturated granular soils with computed tomography

The planned research project deals with the experimental investigation of unsaturated granular porous media such as glass beads and sand by application of the imaging technique of computed tomography (CT). In the framework of substantial experimental research, the macroscopic hydraulic and hydro-mechanical soil-behaviour will be investigated based on conventional laboratory tests and compared to the results of CT-Scans of unsaturated soil specimens on the microscopic grain-to-grain-scale.The investigations focus on the water retention behaviour as well as on the mechanical effects of capillarity, e. g. in the form of capillary cohesion. For this purpose, different experimental set-ups have been devised, allowing for hydraulic and hydro-mechanical tests on unsaturated specimens and their visualisation by CT-images.In a first biennial funding period, the hydraulic and hydro-mechanical experiments will be conducted in the soil mechanics laboratory of the Institute of Geotechnical Engineeringand Construction Management as well as at the Institute of Biomechanics at TUHH, where a desktop micro CT-scanner is situated. The extensive image material will be evaluated with an already existing software and will be thoroughly analysed and interpreted. In an intended biennial continuation period, further CT-investigations under application of synchrotron-based X-ray radiation at the German Electron Synchrotron (DESY) in Hamburg are planned. This allows for even higher spatial resolutions and for the imaging of fast transient effects in unsaturated soil due to short durations of exposure. Furthermore, the experimental investigations are supposed to be supplemented by numerical studies using a Bonded-Particle-Model (BPM) in the framework of the Discrete-Element-Method (DEM), allowing to model capillary bridges in DEM-models derived from the obtained CT-data. Amongst other goals, these studies seek to improve the available capillary bridge models.

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