Better options for managing Amsterdam quays

A quay wall from the 19th century collapsed alongside the Grimburgwal in Amsterdam in 2020. Deltares conducted a study to investigate the causes. With the recommendations from that study, the city wants to reduce the risks relating to quays and bridges, and extend their lifespan.

The Herengracht, Singel, Keizersgracht and Prinsengracht: Amsterdam is famous for its characteristic and picturesque canals. And so the city has a lot of quays and bridges. Most of them – some 200 kilometres of quay wall and around 850 road bridges – are managed by the city authority.

The city has a management organisation that handles the maintenance of the quays and bridges. ‘For years, maintenance in our city was reactive,’ says Annemarij Kooistra of the City of Amsterdam. ‘There were inspections and we intervened when there were problems with the quays. We had no long-term planning for major maintenance or replacing quays. There were plans for upgrades but they ran into problems with lengthy procedures or environmental factors.’

Sustainable and futureresilient

The most sustainable quay wall is the one that can be used longer in its current condition. How can you keep using quay walls for longer? We asked Mandy Korff, a Deltares expert in the field of soil/structure interaction and foundation engineering, and the Associate Professor of Geotechnical Engineering at Delft University of Technology.

Read the interview

Sustainable and future-resilient

How can Deltares help to extend the lifespan of quay walls?

‘Due to overdue maintenance, city authorities often have to make decisions about the maintenance and management of quays quickly and with patchy information. There is often no time for detailed research, and the wide variety of quays in the city makes it impractical to do this everywhere. Deltares is helping to draw up an assessment method, including a safety philosophy that – working from an overall to a detailed picture – helps to assess which quays need to be tackled.

Eventually, this should result in the classification of quays in categories such as old-fashioned brick quays and quays with a concrete superstructure. A clear classification will make it possible to speed up the assessment process. We are also developing an advanced model that can handle uncertainties such as pile quality better than traditional models. We created a simple interface to maximise accessibility for users. They can refine this probabilistic model themselves when they acquire more data. For example, if you find out during an inspection exactly how big the foundation piles are, you can put that information into the model. If you don’t know how big they are, the model works with the available data from across the city so that you also get a solution to the problem. This demonstrates the value of adding measurements and inspections to the assessment and it has generated major savings. Measurements also provide important insights when a quay is being renovated, such as how a new quay affects groundwater run-off towards the canals.’

Which measurement techniques can provide a good picture of the condition of existing quays?

‘Quays are located in part below the waterline and underground, and measurements are not straightforward. We are looking to combine measurement techniques, such as satellite observations that map out an entire city. We combine them with traditional measurements made with equipment on the quays. We are also working on a large collaborative project (LiveQuay) with a range of parties to apply new technologies such as the latest advances in photogrammetry. By taking those pictures at different times and then combining them, you start to recognise patterns and, for example, you see cracks forming over time. We are also conducting studies with vibrations, measuring vibrations generated by traffic and looking at how the structure responds. Or we work with vibrations that we generate ourselves using a device or by positioning a heavy truck on the quay. Combining these techniques produces synergies and allows us to come up with better solutions.’

Studying quay walls in the Deltares GeoCentrifuge

It is expected that tests on quay walls in the Deltares GeoCentrifuge will open the way to extending the lifespan of many existing walls. The trials also contribute to the development of ‘smart’ infrastructure in which sensors can be installed in optimal ways. The partners in this study, including the Port of Rotterdam Authority, aim to cut carbon emissions from the development of port infrastructure by 50%. So a plan was developed to apply a large test load to a wall that was fitted out with sensors. Since this wall is actually in use, it must obviously be kept intact, which is why we are combining these field trials with a series of centrifuge tests in which we can raise the load until the structure collapses and we can vary the soil composition in a series of tests so that the test results can be used widely. We can draw on the results from the measurements in the field trial and centrifuge tests to optimise the computer models.

This study is innovative because it combines a field trial, centrifuge tests and computer models. The knowledge questions addressed relate to the differences between 2D and 3D approaches, the role of differences in stiffness between soil layers, and load variations. We use the input to apply the sensor data to full-scale quay walls. That gives us a clearer picture of the actual soil behaviour with respect to the lifespan. During that work, we are also looking at the effects of climate change.

Subsiding quays

The result was overdue maintenance, with incidents in which quays subsided, and sinkholes at different places in the city. In response, a Bridges and Quays programme was launched in 2018 to tackle the problems in a structural way.

Things went badly wrong again in 2020, when a section of the quay at the corner of Grimburgwal and Oudezijds Voorburgwal, complete with lamppost and all, sank into the water. The University of Amsterdam is the owner of this quay but the city authority came to the rescue and helped the university secure it. ‘We were already in contact with Deltares, TNO and the Amsterdam Institute for Advanced Metropolitan Solutions to develop the programme. We wanted to set up an inspection and monitoring system, and develop an assessment method for the bridges and quays. When the Grimburgwal quay collapsed, we wanted to learn from what had happened. What caused the collapse, and how can we stop this happening again in the future?’

Bed depth

Deltares studied the collapsed quay in detail and shared its recommendations with the City of Amsterdam, which is now using them in its current approach to the maintenance and management of the quays and bridges. ‘The depth of the bed, for example, is an important factor for the stability of the quay and how long it will last. We adjusted the inspections and monitoring accordingly by looking more specifically at bed depth.’

The knowledge Deltares is developing with its partners also allows the city authority to make better decisions about replacing quays. ‘The study showed that if you distribute the load on a quay differently, the quay lasts much longer. We can also make a better assessment of whether to repair certain parts, such as the foundation piles, of a quay or bridge instead of replacing them entirely. And this knowledge gives us a broader range of options, from doing nothing to complete demolition and rebuilding.’

Nature-inclusive

Does climate change still play a role in the management of the quays and bridges? ‘Falling groundwater levels because of climate change lead to subsidence and that can undermine the foundations. But because the foundations of quays and bridges are near canals or watercourses, this factor plays a smaller role. Moreover, the water level in our city water is kept constant, and we are less vulnerable.’ However, the city does take climate change into consideration in the replacement programme involving the construction of new quays. ‘We are making those quays nature-inclusive by allowing ferns to grow near the bridges and creating cavities where animals can shelter. That is good for biodiversity and helps to make our city climate-adaptive. Trees alongside the quays also play an important role here because they keep the city cooler.’

Annemarij Kooistra

Programme manager in the City of Amsterdam’s Engineering department

International

A lot of work will have to be done and it will take years. Amsterdam has therefore been working with the other three large Dutch cities of Utrecht, Rotterdam and The Hague in recent years. ‘We exchange knowledge with each other.’ This work is also being done in the Inner City Quay Walls Platform and the Bridges Platform. In addition, a City Deal for the renovation of historic inner cities is starting up, with the parties looking at new working methods and standards for the management of quays and bridges. ‘There are also international contacts, for example with Belgian cities.’