Impact of Cyclic Loads and Subsurface Weaknesses on the Behavior of a Deep-Sea Quay Wall
A.Z. Chat (TU Delft - Civil Engineering & Geosciences)
K.G. Gavin – Mentor (TU Delft - Civil Engineering & Geosciences)
M. van Koningsveld – Graduation committee member (TU Delft - Civil Engineering & Geosciences)
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Abstract
Deep-sea quay walls in the Port of Rotterdam have been extensively constructed in the last 150 years and have been subjected to cycles of unload and reload of surcharge load along with fluctuating water levels. These cyclic load conditions significantly impact the continuous development of deformations in the quay walls and the forces in the structural elements over a long term. This study presents a detailed analysis of the long-term behavior of the quay wall located in the Hartel Tank Terminal at the Port of Rotterdam. This study also considers the effect of deeply embedded thin clay layers on the bearing capacity of the screw injection
(SI) piles. Previous research by Rica and Van Baars (2018) and Chai et al. (2022), among many others, have shown that the subsurface weaknesses, especially due to presence of deep clay layers, have a significant impact on the end bearing capacity of the closed ended piles loaded under compression. This effect depends on the location of the clay layer with respect to the zone of influence of the pile.
The two major structural responses observed in the behaviour of the quay wall is the accumulation of horizontal wall displacements and continuously increasing anchor forces in the tension piles over long-term application of the cyclic surcharge loads. The progressive increase in the anchor force is a direct result of the continuously increasing horizontal displacements of the wall.
Clay layer present in the deep Pleistocene sand in the vicinity of the tips of the bearing piles was shown to have a negative impact on the mobilised base resistance of the piles. In the case of a quay wall with a relieving platform and a bearing and tension pile trestle with inclined pair of bearing piles, where the complete load bearing capacity is derived only from the deep bearing sand layers, the impact was most significant i.e. at least a 10% reduction, when the clay layer was present from 3D below the pile tip to 1.5D above the pile tip, D being the equivalent diameter of the SI piles. The maximum reduction in the mobilised base resistance
was observed to be 38% when the pile tips were in the middle of the clay layer, with half the clay layer above and half below the pile tips.
This study provided valuable insights into the long-term deformation behaviour of the quay wall under cyclic operational and water loads. It also provided critical reasons to enhance site investigations to look for any subsurface weaknesses in the vicinity of structural elements and to optimise the pile design, such as embedment length, as per the actual subsurface conditions.