Dikes on Peat: Improved Design Method Available
Dikes on Peat are stronger than has been assumed in the past. Until now, it has not been possible to calculate exactly how strong they are. However, advances have been made.
On the basis of field trials, software analyses, laboratory and model experiments, research institute Deltares, working together with Rijkswaterstaat and the Hoogheemraadschap Hollands Noorderkwartier water authority, has devised an improved calculation and design method.
The method was developed specially for the dikes of the Marken Lake but some elements from the study are ultimately applicable to a range of dikes on peat.
After a positive assessment from the Flood Management Expertise Network, the Ministry of Infrastructure and the Environment has given its approval to using the method for the Marken Lake dikes.
The design method was developed on the basis of a unique series of field trials. The results of those trials indicated that peat is stronger than previously thought.
The knowledge generated by the field trials was supplemented by software analyses from the Dike Analysis Module, tests in the GeoCentrifuge and laboratory studies, resulting in a new, improved, design method specifically for the Marken Lake dikes.
Steps to determine peat strength
The design method sets out how the peat strength can be determined for the Marken Lake dikes in a number of steps and be included in the design calculations.
· Conducting field probe measurements;
· Conducting laboratory tests (DSS Direct Simple Shear Tests for peat);
· Correlating the results from the laboratory tests with the field probe findings and the subsequent derivation of calculation parameters;
· Conducting stability calculations with an analytical slip-plane model (DGeoStability, LiftVan method, Bishop and Spencer van der Meij) in combination with undrained strength properties.
Possibility of less drastic upgrading
The new design method will have an immediate impact on the upgrade of the Hoorn – Amsterdam dike. A better understanding of the strength of the peat could make it possible to reduce costs and make the operation less drastic.
Calculations using the new design methodology are now being made for the entire dike section. It will become clear during the course of this year how much money can be saved.
This approach will match the approach being developed as part of the national Statutory Assessment Instrument 2017 program.