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

现浇混凝土桩是解决非承重地基基础的典型方法。此外，在预期荷载高度集中的情况下，可以采用灌注桩群。但如果群桩间距过近，则新桩安装过程中引起的桩身振动会影响原桩的水化过程。从而影响了早期混凝土的强度发展。潜在的桩缺陷可能导致严重的后果，特别是考虑到目视检查任何桩缺陷是不可能的。这种情况背后的土壤动力系统是非常复杂的：(1)源（打桩）；（ii）介质（在近场和远场中具有非弹性波传播的土壤），（iii）接收器（具有暴露在振动中的新混凝土或早期混凝土的相邻桩）。在过去，这些复杂的依赖关系没有经过充分的科学研究。本课题的研究目标是开发一种将岩土波传播模型与材料科学中的混凝土模型相结合的模型，以保证现浇混凝土群桩生产过程中的质量。为了实现这一目标，工作计划包括现场调查、数值模拟以及实验实验室工作。实地调查的目的是在实际条件下描述系统，并确定数值模拟的输入参数以及实验测试的设置。在现场验证的数值模型的基础上，进一步研究了驱动能量、土壤条件、几何因素等不同参数的影响。在相关的实验室研究中，新混凝土和早期混凝土暴露于振动中以模拟现场条件，并研究振动对后期混凝土阻力和耐久性参数的影响。最后，对岩土和材料结果进行整理，形成一个工程模型，使现浇混凝土群桩的设计和生产得到科学验证。工程模型的一个结果可能是在考虑土壤条件、驱动能量、桩距等因素的情况下，在开始相邻桩的打入过程之前，通过指示足够的混凝土成熟度来防止生产过程中混凝土的损坏。

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.