Inclination behaviour of historic quay walls

Abstract

The inner-city of Amsterdam contains a large network of vulnerable, historic quay walls. Most of these quay walls consist out of masonry gravity walls placed on wooden relieving floors and wooden foundation piles. Due to the changing surface loading conditions behind the wall and the degradation of the masonry and wooden structures over the last century, the safety of the quay walls is in critical condition. Insight into the behaviour of the masonry wall tilt and its relationship with several failure mechanisms is still limited. Therefore, the objective of this thesis is to provide this insight into the behaviour of the tilt approaching failure in the center of Amsterdam. Additionally, the use of monitoring data from SmartBrick devices is analyzed to assess the value of quay wall inclination monitoring.

Using PLAXIS 2D, quay wall models are made aimed to create a sensitivity analysis towards the wall tilt using multiple variations in quay structure dimensions and parameters. These variations investigate the wall height, wall thickness, floor length (and the amount of pile rows), the canal depth and the pile diameters based on a typical Amsterdam soil profile. For the tested geometry variations, there is a linear relationship seen between the wall tilt and the horizontal wall displacement towards the canal, during the addition of the surcharge load behind the wall. The relationship between the wall tilt and the surcharge load is predominately linear at lower/realistic surface loads, at higher loads, towards failure, the wall tilt becomes exponentially larger, this is also seen by setting the varied dimensions towards failure scenarios. The most sensitive variations for inclination are the change in the masonry wall height and thickness, the pile distribution underneath the floor and the addition of a surcharge load directly behind the masonry wall.

The failure mechanism describing the horizontal displacement of the masonry wall and the piles is recognized by increasing the height of the masonry wall and by decreasing the pile diameters (pile degradation). By increasing the wall height, the quay structure also settles vertically, which in combination with the horizontal displacement, initiates wall tilt. During the addition of the surcharge load, the crossbeam (kesp) and the piles can deform, and their bending moments can exceed their bending capacity, indicating another failure mechanism with initiates wall tilt. The failure mechanism describing rotation of the masonry wall on the floor towards the canal is activated by decreasing the wall thickness and therefore decreasing its lateral capacity. This causes the masonry wall to fall over. Damage to the foundation elements has an important impact on the tilt of the wall, due extensive axial displacements of the front pile row or cracks in the masonry wall.

To compare the SmartBrick inclination and PLAXIS inclination, it is important to know the exact degradation, erosion and loading conditions during the time between two SmartBrick measurements. The linear relation between the wall inclination and the wall displacement is useful for SmartBrick because it shows that monitoring the inclination also predicts the wall displacement and the state of the quay wall. Pile degradation and canal erosion only give a small wall tilt increase, but a larger increase in horizontal displacement of the wall is seen. Therefore, high measuring accuracy and resolution are necessary to monitor only the wall tilt.

To conclude, approaching quay wall failure shows that wall tilt in combination with horizontal displacement is expected, this behaviour can be monitored using SmartBrick. High wall tilt is often a first consequence of the exceedance of the bending capacities in the wooden elements.