Waves test the strength of clay in sea walls
At the end of June, the Noorderzijlvest Water Authority commissioned tests on clay blocks from the sea dike behind Bierum. These tests are being conducted in the Delta Flume at the Deltares research institute in Delft. By simulating large waves in this flume, researchers are investigating the strength of both clay blocks covered with grass and clay from the interior of the dike. The tests will continue until mid-August.
Abrasion of waves
The tests are being conducted using 30 large blocks of clay measuring 2m x 2m x 0.8m from the Eemsdijk near Bierum. By testing both the clay from the top layer and from the core, researchers are investigating the extent to which erosion of clay by wave action affects water safety. This will help determine when and to what extent dikes need to be reinforced in response to rising sea levels caused by climate change.
Testing the erosion resistance of clay
The tests are part of the 'Clay Erodibility Study'. In addition to the tests in the Delta Flume, the water board is investigating nine different types of clay from four different locations along the Wadden Sea and Eems Dollard. A combination of small, simple tests has been selected for the clay types to map their properties. These small tests are carried out with clay that has already been tested in the Delta Flume. Their erodibility is therefore known. The results of the tested clay from the Delta Flume are compared with the results of the small tests. In this way, Noorderzijlvest, together with Deltares, is investigating which small tests (combined) are most useful for predicting erodibility.
Borehole erosion test
Another part of the erosion resistance study is Fugro's borehole erosion test. This is a new test, originally devised by American dyke builders and now further developed by Fugro. In this test, a 4 m deep hole is drilled in the dyke. Water is then flushed through it at a constant speed for 10 minutes. The enlargement of the borehole due to soil washout is measured accurately. This indicates how resistant each soil layer is to erosion by flow and waves. The aim of the entire study is to develop a simple method for determining the erodibility or 'wear resistance' of clay.
Use local soil
In the coming years, many kilometers of dykes in the Netherlands will need to be reinforced. This requires a large amount of clay. According to the current rules, not every type of clay is suitable for this purpose. The results of the studies provide information about how the properties of clay contribute to its strength. By taking a broader view, it may be possible to use certain types of clay from the region and reuse them. This would eliminate the need to transport clay from far away, saving costs and reducing CO2 emissions.
Collaboration
The Noorderzijlvest Water Authority is conducting the 'Clay Erodibility Study' in collaboration with Deltares, Fugro, and Wiertsema & Partners. The High Water Protection Program (HWBP) is subsidizing the study.