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

本课题拟应用计算机断层扫描成像技术（CT）对玻璃微珠、砂土等非饱和颗粒状多孔介质进行实验研究。在大量实验研究的框架下，将在常规实验室试验的基础上研究宏观水力和水力学土的行为，并将其与微观颗粒尺度上非饱和土样品的ct扫描结果进行比较。研究的重点是保水行为以及毛细作用的机械效应，例如毛细内聚力的形式。为此目的，设计了不同的实验装置，允许对非饱和试样进行水力和水力力学测试，并通过ct图像将其可视化。在第一个两年资助期内，水力和水力力学实验将在岩土工程和建设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，该研究所设有台式微型ct扫描仪。广泛的图像材料将用现有的软件进行评价，并将进行彻底的分析和解释。在计划的两年延续期内，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射线辐射进行进一步的ct研究。这允许更高的空间分辨率和成像的快速瞬态效应在非饱和土壤中由于暴露时间短。此外，实验研究应该得到数值研究的补充，使用离散元法（DEM）框架下的结合粒子模型（BPM），允许在从获得的ct数据导出的DEM模型中模拟毛细管桥。在其他目标中，这些研究寻求改进现有的毛细血管桥模型。

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.