The influence of pile-driving induced vibrations on the hydration ofearly-age concrete regarding cast-in-place concrete pile groups

钻孔灌注桩是非承重土地基处理的典型方案。此外，在预计荷载集中度较高的情况下，还可以使用成组灌注桩。然而，如果这样一组桩之间的距离太近，最后一根桩的安装过程中打桩在地基中引起的振动可能会破坏先前准备的桩的水化过程。从而影响了早龄期混凝土的强度发展。潜在的桩缺陷可能会导致严重的后果，特别是考虑到任何桩缺陷的目视检查都是不可能的。这种情况背后的土壤动力系统是非常复杂的：(I)源(打入桩)；(Ii)介质(近场和远场具有滞弹性波传播的土)；(Iii)接收器(邻近的桩和新鲜或早龄期混凝土暴露在振动中)。过去，这些复杂的依赖关系没有经过充分的科学调查。研究方案的目标是开发一种将岩土波传播模型与材料科学的混凝土模型相结合的模型，以便在现浇混凝土群桩的生产过程中实现质量保证。为了实现这一目标，工作方案包括现场实地调查、数值模拟以及实验室实验工作。现场调查的目的是描述实际条件下的系统，确定数值模拟的输入参数以及实验测试的设置。基于现场调查得到的经过验证的数值模型，进一步的数值模拟研究了不同参数的影响，如驱动能量、土壤条件、几何方面等。在相关的实验室调查中，新鲜混凝土和早期混凝土受到振动的影响，以模拟现场条件，并研究振动对后期混凝土抗力和耐久性参数的影响。最后，岩土和材料成果的汇编应产生一个工程模型，使现浇混凝土群桩的设计和生产能够得到科学验证。工程模型的一个结果可以是诺模图，通过在开始相邻桩的打桩过程之前指示足够的混凝土成熟度来防止生产过程中的混凝土损坏，同时考虑到土壤条件、驱动能量、桩距等。

Cast-in-place concrete piles are the typical solution for foundations in non-load bearing soil. In addition, groups of cast-in-place piles are possible in cases where high load concentrations are expected. However, is the distance between the piles in such a group too close, the pile driving induced vibrations in the subsoil due to the installation process of the latest pile could impair the hydration process of the previously prepared piles. Thus, the concrete strength development of the early-age concrete is affected. Potential pile defects could lead to serious consequences, especially considering that visual inspection of any pile deficiency is impossible. The soil dynamic system behind this situation is very complex: (i) source (driving pile); (ii) medium (soil with anelastic wave propagation in the near and far field), (iii) receiver (adjacent pile with fresh or early-age concrete exposed to vibrations). In the past, these complex dependencies had not undergone adequate scientific investigation. The objective of the research proposal is to develop a model that combines the geotechnical wave propagation models with the concrete models from material science in order to enable quality assurance during the production process of cast-in-place concrete pile groups. To achieve this objective, the working program covers in-situ field investigation, numerical simulations as well as experimental lab work. The field investigations aim to describe the system under realistic conditions and to identify the input parameters for the numerical simulations as well as the settings for the experimental tests. Based on the validated numerical model from the field investigation further numerical simulations study the effect of different parameters involved, e.g. driving energy, soil conditions, geometric aspects, etc. In associated laboratory investigations fresh and early-age concrete are exposed to vibrations to mimic the on-site conditions and to study the effect of vibrations on the later concrete resistance and durability parameters. Finally, the compilation of the geotechnical and material results shall lead to an engineering model that enables a scientifically proven design and production of cast-in-place concrete group piles. One outcome of the engineering model could be nomograms to prevent concrete damage during the production process by indication of adequate concrete level of maturity before starting the driving process of the adjacent pile under consideration of the soil condition, driving energy, pile distance, etc.