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

点击翻译按钮获取中文摘要

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.