The UvA commissioned geodata specialists Fugro to investigate the collapse of the quay wall, which was around 150 years old. Based on a comprehensive analysis of available data and visual inspections, Fugro’s final report concludes that multiple causes led to the quay wall collapsing:
- Location. The quay wall is situated at the end of another canal, namely the Oudezijds Voorburgwal canal. Boats (e.g. canal cruise boats) make a turn here. This causes additional (and significant) loads against the quay wall, consisting of outflow, wave and impact loads. Consequently, both the friction wood and the masonry next to it sustained damage, perhaps also adversely affecting the structural integrity of the quay wall.
- In addition, the canal bed level is relatively low at this point due to excavation work, which has a detrimental effect on the quay wall’s stability. This also increases the risk of piping (water flow) and soil movement under the quay wall, especially if ground screens are too short and/or in poor condition. This leads to subsidence, as was also observed earlier, in mid August, prior to the quay wall’s collapse.
- The construction method of the (partially collapsed) quay wall, which entailed the use of only two foundation piles per row, is more vulnerable than it would be if three foundation piles had been used. Such a structure is less capable of supporting a horizontal load. Furthermore, there is a relatively large retaining height (height of the quay wall relative to the Amsterdam Ordnance Datum) and the piles might not all have been driven in a load-bearing layer of sand.
- The time of collapse (September 2020) is partly explained by the heavy precipitation over the course of the preceding month.
Ownership and costs
The ownership of the quay was unclear until the incident. To identify the owner, the UvA commissioned historical research from the Netherlands’ Cadastre, Land Registry and Mapping Agency (Kadaster). According to the Kadaster, the UvA owns the section between the fencing (to the rear of the UvA buildings). The section along the public road and bridge is owned by the City of Amsterdam.
The cost of the repair work to date is approximately €1.1 million. This pertains to the investigation, the clean-up of the debris and the erection of an emergency structure with sheet piling. Due to the quay’s listed status, the UvA and the City of Amsterdam will work in tandem on the final repairs. It has been agreed that these final repairs will be complete within five years. The costs that this will entail are not yet known and will become clear after the final repair work has been put out to tender.