Experimental investigation and development of a theoretical model for the vibrofluidisation of dry granular materials

拟议的研究项目的目的是开发一个理论模型，用于描述干燥的粒状材料，如砂的振动流化，基于岩土实验室试验的结果。然后，这个理论模型应该被转换成一个材料模型，适用于执行到一个有限元程序，以解决以后复杂的岩土边界值problems.In这种情况下，振动流化是指出现的流体性质的颗粒材料受到振动与大的加速度振幅。类似流体的性质是例如降低的剪切强度或完全缺乏剪切强度、粘性应力分量和流体静力应力状态或对流运动的演变。虽然岩土工程界早已认识到这种现象的存在，但对其研究很少，解释方法也不完善。由于最近的研究结果表明，相关的振动流化的施工技术，如振动打桩和振动压实，需要进一步的研究，可以清楚地说明。 该研究项目的重点是变形行为和剪切强度降低的粒状材料，而受到振动。后者归因于振荡颗粒引起的碰撞应力的出现、惯性力引起的有效应力的减小以及稳定颗粒运动引起的动摩擦的减小。实验工作将包括用于调查压实行为的体积测量试验以及用于调查振动期间的剪切强度的三轴试验。为此，将传统的电池安装在振动台上并进行修改，以便可以连续施加载荷。模拟振动条件下砂土地基沉降的模型试验将作为验证材料模型的一种手段进行。开发该材料模型将是理论工作的主题，以及将其实施为有限元程序，并使用已执行的实验室试验结果进行验证。

The aim of the proposed research project is the development of a theoretical model for describing the vibrofluidisation of dry granular materials like sand, based on the results of geotechnical laboratory tests. This theoretical model is then supposed to be transferred into a material model suitable for implementation into a finite element program in order to solve later complex geotechnical boundary value problems.In this context, vibrofluidisation means the emergence of fluid-like properties within a granular material subject to vibrations with large acceleration amplitudes. Fluid-like properties are, for example, a reduced shear strength or complete lack thereof, viscous stress components and hydrostatic stress states or the evolution of convective motions. Although the existence of this phenomenon has long been known in the world of geotechnical engineering, only few studies and incomplete approaches toward it’s explanation exist. Since recent findings suggest the relevance vibrofluidisation has for construction techniques like vibratory pile driving and vibrocompaction, a need for further research can clearly be stated. The research project focusses on the deformation behavior and shear strength reduction of granular materials, while being subjected to vibrations. The latter is attributed to the emergence of a collisional stress caused by oscillating grains, the reduction of effective stresses due to inertial forces and the reduction of mobilized friction due to steady grain movements.The experimental work will consist of oedometric tests for investigating the compactive behavior, as well as triaxial tests for investigating the shear strength during vibration. For this purpose, conventional cells will be mounted on shaking tables and modified, so that the loading can be applied pneumatically. Model tests simulating the settlements of a foundation on sand under vibrations will be performed as a means of validating the material model.Developing this material model will be the subject of the theoretical work, as well as the implementation into a finite element program and the validation with the results of the executed laboratory tests.