Investigation of capillary effects on the grain scale by means of in situ experiments, imaging and numerical simulations
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
In the framework of this habilitation thesis, the application of in situ (imaging) experiments, i. e., experiments run in an imaging environment, for studying geomechanical problems with focus on unsaturated granular soils is motivated and discussed. By means of computed tomography (CT), a non destructive imaging technique frequently applied in materials science, but also by means of much simpler imaging techniques, and custom-built experimental set-ups with geomechanical background, different processes in unsaturated granular soils are studied. In the thesis, different miniaturised set-ups for such "in situ (CT) experiments" are presented and applied to study (1) the shear strength and hydro-mechanical coupling and (2) the water retention behaviour of unsaturated granular media, based on the example of a coarse grained model sand and packings of artificial soda-lime glass beads. The data obtained from a temporal sequence of 2D or 3D images in in situ imaging experiments is visualised and analysed to investigate the microscale soil behaviour. By studying "capillary state variables", e. g., fluid clusters and interfacial properties, such as interfacial areas, the acquired image data allow for quantitative insights into the shear behaviour and water retention behaviour on the grain or pore scale. This helps to improve our understanding of links between the microscopic and macroscopic soil behaviour which is represented by shear strength, capillary cohesion, volume change or the water retention curve. Besides a discussion of different other experimental applications of in situ CT experiments with a geomechanical background, the thesis gives an outlook on numerical modelling based on CT data as geometry model input in particle or mesoscopic models which could lead to a so-called "virtual soil lab", allowing to study the hydro-mechanical behaviour of soils on a digital simulation-based basis. In this context, the application of the Finite-Discrete Element Method (FDEM) with granular CT data as input as well as the multiphase Lattice Boltzmann Method (LBM) for the simulation of multiphase flow in digitised pore spaces from CT data is presented.
Teilgesättigte granulare Böden