The behaviour of a flexible dolphin in the Port of Rotterdam

Abstract

The objective of this thesis is to enhance understanding of the behaviour of a flexible dolphin and its interaction with the surrounding soil in order to determine the optimal embedded depth. A comprehensive field test is conducted to gain deeper insights into the behaviour of the flexible dolphin and the soil surrounding the pile. The test measurements are then analysed to assess the pile's behaviour. Additionally, calculation models are employed to predict the pile's behaviour, and a comparison is made between the measurements and predictions.
Four different calculation models, namely Blum, Brinch Hansen, P-y curves, and Plaxis are utilized to predict the pile's behaviour during the test. The pile behaviour is compared across these models. While most models do not account for repetitive loading, the best available inputs are employed to simulate the test as accurately as possible. The majority of the models exhibit similar top displacements of 0.9 meters, except for the drained Plaxis model, which calculates displacements of 1.05 meter, and Blum's model, which calculates a displacement of only 0.8 meters.
During the test, multiple instruments are employed to measure various parameters of the pile, including load, displacement, water pressures, and strains at different depths and time intervals. The total station measurements indicate a maximum displacement of nearly 0.7 meters, which differs by 0.2 meters from the predictions.
The deviation between the predictions and measurements can largely be attributed to inaccuracies in the hydraulic jack load measurements. The pile load was back-calculated using the strain data obtained from the pile. The loads estimated based on the strain measurements were found to be hundreds of kilonewtons lower than the hydraulic jack load measurements. As the strain measurements were considered more reliable, the actual load during the test differed from the prescribed load scheme. Consequently, the load inputs in the models need to be adjusted to align with the loads derived from the strain data.
The displacement measurements are analysed and compared with each other. The Saaf and optical fibre measurements exhibit similar curvatures, enhancing the reliability of the optical fibre strain measurements during load analysis. However, the total displacement measured by the Saaf and the total station do not match due to the incorrect assumption of zero movement at the pile tip. Determining the exact displacement of the entire pile is impossible due to the inadequate number of boundary conditions available to translate the Saafs curvature measurements into displacement.
The calculation models utilize the loads derived from the strain measurements to make predictions, and their results align comparably with the measurements. Plaxis is the only model capable of simulating different load cycles, which improves the comparability of the Plaxis results with the test.
Load-displacement graphs obtained from the Plaxis results and the optical fibre measurements display hysteresis in load cycles, consistent with findings in existing literature. The initial load exhibits less stiffness compared to the repetitive loads in both datasets. The amount of energy absorption by the soil is determined from the areas of the loadcycles. When considering the most complete load cycles, Plaxis conservatively estimates the absorbed energy.
Reducing the length of a pile results in larger displacements of the pile, while concurrently enhancing its capacity for energy absorption. However, it is crucial to strike a balance between these two parameters, while paying close attention to the permanent soil displacements.