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

计划中的研究项目是应用计算机层析成像(CT)技术对玻璃微珠和沙子等非饱和颗粒多孔介质进行实验研究。在大量实验研究的框架内，将基于常规的实验室试验来研究宏观的水力和水力学特性，并将其与微观颗粒尺度上的非饱和土样的CT扫描结果进行比较。研究的重点是土壤的保水特性以及毛细作用的力学效应，例如毛细凝聚力的形式。为此，设计了不同的实验装置，允许对非饱和试件进行水力和流体力学测试，并通过CT图像进行可视化。在第一个两年期的资助期间，水力和流体力学实验将在岩土工程和建筑管理研究所的土壤力学实验室以及TUHH的生物力学研究所进行，台式微型CT扫描仪就位于那里。大量的图像材料将用现有的软件进行评估，并将进行彻底的分析和解释。在预定的两年期延续期内，计划在汉堡的德国电子同步加速器(DESY)应用基于同步加速器的X射线辐射的情况下进行进一步的CT调查。这允许更高的空间分辨率，以及由于短时间曝光而在非饱和土壤中的快速瞬变效应的成像。此外，实验研究应该得到在离散单元法(DEM)框架内使用键合粒子模型(BPM)的数值研究的补充，允许在根据所获得的CT数据导出的DEM模型中对毛细管桥进行建模。除了其他目标外，这些研究还寻求改进现有的毛细管桥模型。

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.