Field trials carried out by Deltares have shown that a peat substrate is stronger than was previously thought.
The trials lasted a year and were performed during reinforcement work on the Markermeer dike between Hoorn and Amsterdam. The dike, built on peat soil, no longer complied to the latest safety standards legislation. That is why the dike is being raised or widened at certain points.
A calculation model is used to determine how much reinforcement is required in such cases. Experts had suspected for some time that this model was underestimating the strength of peat, which is why it was decided to perform field trials. The results confirmed that peat is stronger than previously thought and that the calculation model would have to be modified.
Cor Zwanenburg is the project manager at Deltares for the Markermeer trials: ‘ We know a great deal about how clay and sand behave as a substrate, but not peat. The trials are a useful starting point. They have already generated new information on the strength of peat and how it can fail, and they confirm what experts had suspected. They also demonstrate the need to modify the models currently used to calculate the strength of peat underneath dikes.’
The results cannot, however, be applied directly. Zwanenburg: ‘ Peat consists of plant material, which means the composition and strength differ from place to place. You have to take that into account, so to improve model accuracy a further step is necessary.’
The new calculation model is not just important for the Netherlands. Peatlands exist in other places too, so there is considerable international interest in the trials. Zwanenburg: ‘ Other countries may not have dikes on peat substrates, but other structures such as roads or railways. Our findings are relevant to those structures as well.’
Deltares performed the Markermeer trials at the request of the North Holland Regional Water Board and Rijkswaterstaat (part of the Ministry of Infrastructure and the Environment). The trials started in October 2011, were carried out in a meadow near Uitdam just behind the Markermeer dike, and took a year to complete.
[mappress]
Press Release, November 28, 2012