The economic heart of the Netherlands, the Randstad, is predominantly built on soft clay and peat layers. The urban and rural areas of the Randstad are contending with subsidence and this is affecting habitability. Every year, subsidence causes more damage; damage due to flooding, damage to roads and railways, dikes, pipelines and buildings. This is placing an ever greater strain on government bodies, businesses and residents. Clearly, something must change; but where do we start?
Deltares set to work with the executives and officials of the municipalities of Gouda and Almere, to present them with an agenda for tackling subsidence. This agenda made it clear whether the measure is proactive (tackles the cause) or reactive (tackles the consequences of subsidence) and whether responsibility rests with public or private parties. This is a way of identifying measures that are likely to succeed. The perspectives clarify the discussion: who will be doing what, and when.
Almere is the fastest-subsiding municipality in the Netherlands. Because of this, construction has always been accompanied by sizeable embankments. Deltares has mapped the geological structure of Almere. This study reveals that locally occurring peat layers in the subsoil are a major factor in the settling of the subsurface in Almere. The heterogeneity of the subsoil results in major settling differences in relatively small areas, which in turn causes severe damage to roads and infrastructure. The upper layers of sand and clay, several metres thick, tightly compress the underlying peat. Deltares has shown the effects of this on the management and maintenance of public space.
Woerden is setting up the experiment to compare different foundation techniques. Deltares undertook research and advised on the three most suitable techniques for establishing a trial zone. Trial zones will be created in 2016 and the behaviour of the roads and the subsoil will be monitored.
Economically and socially responsible decisions can only be taken on the basis of reliable knowledge of the behaviour of the roads and subsoil. Experiments like the trial foundation zones are necessary in order to make an objective comparison and a sound choice of construction, management and maintenance strategy.
Investments in the management and maintenance of infrastructure have to be more sustainable and controllable. Because of this, we need more knowledge.
In this project Deltares worked together with the following partners: