| Popis: |
During excavations, steel sheet piles are often installed through vibratory driving. This is especially effective in soft soils. However, when installing sheet piles in other soils such as glacial till, there is a risk of impact with boulders that may damage the sheet pile toe. This may result in unnecessary time- and cost intensive measures to ensure stable and watertight excavation. Hence, there is a need for a criterion to stop the driving before the sheet pile is severely damaged. The purpose of this paper is to investigate how numerical models may be used to simulate a sheet pile encountering a boulder during vibratory driving, and to investigate the possibility of developing a stop criterion based on the outcome of themodels. Two numerical models were created to simulate the vibratory driving: a uniaxial multi degree of freedom model and a finite element (FE) model, by using the numeric platform MATLAB and the FE software ABAQUS respectively. The simulations were carried out through explicit time integration in both models. The external actions on the sheet pile, i.e., the vibratory driving force, soil resistance and obstacle resistance were estimated with methods found in literature. The models were then calibrated against a field study by using its results as input to the models. The encounter with a boulder, was simulated in different ways. In the uniaxial model, the contact was modeled by an elastoplastic contact force and in the FE model a solid body with high stiffness was introduced. The results of the numerical models show promising resemblance with the results of the field study. Both the global driving speeds and the accelerations of the sheet pile corresponds well with the field study for both models. The simulations indicate that boulder impacts may be detected by monitoring changes in acceleration amplitude traveling along the sheet pile. This suggest that a stop criterion for vibratory driving could be based on abrupt changes in acceleration amplitude. By creating a device with accelerometers detecting a significant increase in acceleration amplitude, damage to the sheet pile could be prevented. Although it should be mentioned that at weak impact points of the sheet pile cross section only small changes in the accelerations were seen in the simulations. |
