Urban quay walls: A numerical study to recognize foundation defects via masonry damage patterns

Abstract

The city of Amsterdam has a large number of old quay walls with rotten foundation piles. These foundation piles need to be identified and measures need to be taken. The urban quay walls are supported by two types of foundation: pinewood piles, which are easily affected by bacterial decay and spruce piles. To understand the mechanical behaviour of quay walls better, it is needed to know the type of wood used for each pile foundation along the 200 km of quay walls currently showing signs of damage. For that reason, specialized diving teams are hired to identify the rotten piles and foundation defects, to know which foundation piles need replacement. Since the area is very large and diving inspections are costly and lengthy in time, there is a need to correlate the foundation defect to the masonry damage above the water level. The masonry above the water level could give lots of information about the condition of the foundation, due to cracks or deformations in the masonry. This research could help to relate foundation defects with damage patterns in the masonry. Understanding this relation helps to identify foundation defects at an earlier stage and helps the municipality to prioritize the replacement of foundation piles. The thesis aims to find indicators above the water line to identify foundation problems by studying the crack patterns in a typical unreinforced masonry quay in Amsterdam. From the point of view of the masonry structures, failure of foundation piles results in a settlement deformation causing cracking. This research will support the current work by Sweco in helping to find foundation defects from above the waterline via masonry damage patterns in quay walls. This will be achieved by performing a parametric study, bases on 2D nonlinear finite element analyses, varying the extent of the pile defects, the material properties of the masonry and lateral boundary conditions for a selected representative base case. To simulate the damage in masonry, a smeared crack approach was used. The foundation defects were simulated by applying a settlement deformation to the quay wall. A Gaussian settlement deformation profile was imposed and the ratio between the length of the profile and the length of the quay wall was varied to simulate the failure of single or multiple piles. To capture the influence of the material properties of masonry (especially related to tension failure), three types of masonry were defined: weak, average and strong. The influence of the boundary conditions at the edges was checked by performing analyses with horizontally free lateral sides and with horizontally fixed lateral side. This is done to simulate the effect of arching in the structure. Eventually, the influence of the location of the foundation defect was analyzed by comparing a symmetric Gaussian settlement deformation with an asymmetric settlement. The analyses show correlations between the vertical displacement at the top of the structure and the length of the settlement profile. As expected, this can be interpreted with the fact that if several piles are damaged simultaneously, a larger portion of the quay wall is cracking. The material properties of the masonry influence the development of crack patterns. The stronger is the masonry, meaning increasing the values of Young’s modulus, tensile strength and fracture energy, the larger is the settlement displacement needed to obtain the same crack pattern. The lateral constraints contribute mostly to the development of the horizontal crack since no horizontal cracks appeared in situations without these constraints. Since the influence of additional loads is not considered in the analysis and the model is modelled in 2D it is recommended to analyze the influence of both in further studies. It is also recommended to validate the model against field measurements since no verification has been done.