Waves test the strength of clay in sea dykes
At the end of June, testing Noorderzijlvest Water Authority on clay blocks from the sea dyke Bierum, commissioned by Noorderzijlvest Water Authority . These tests are being conducted in the Delta Flume at the Deltares research institute in Delft. By simulating large waves in this flume, dyke investigating the strength dyke both grass-covered clay blocks and clay from the interior of the dyke . The tests will continue until mid-August.
Wave scouring
The tests are being conducted using 30 large clay blocks measuring 2 m x 2 m x 0.8 m, taken 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 caused by wave scouring affects water safety. This helps determine when and to what extent dykes need to be dykes in the face of rising sea levels resulting from climate change.
Testing the erosion resistance of clay
The tests are part of the “Clay Erosion Study.” In addition to the tests in the Deltagoot, the water authority is investigating water authority different types of clay from four different locations along the Wadden Sea and Eems Dollard. For these clay types, a combination of small, simple tests has been selected to map the clay’s properties. These small tests are conducted using clay that has already been tested in the Deltagoot. Their erodibility is therefore known. The results of the clay tested in the Deltagoot are compared with the results of the small-scale tests. In this way, Noorderzijlvest, together with Deltares, is investigating which small-scale tests (in combination) are best suited for predicting erodibility.
Borehole erosion test
Another component of the erodibility study is Fugro’s borehole erosion test. This is a new test, originally devised by American dike builders and now further developed by Fugro. In this test, a 4-meter-deep hole is drilled into the dyke. Water is then flushed through the hole at a constant rate for 10 minutes. The enlargement of the borehole due to soil washout is accurately measured. This indicates, for each soil layer, how well it resists erosion by currents and waves. The goal of the entire study is to develop a simple method for determining the erodibility, or “wear resistance,” of clay.
Use locally sourced soil
In the coming years, many kilometers dyke in the Netherlands will need dyke reinforced. This requires a large amount of clay. Under current regulations, not every type of clay is suitable for this purpose. The results of the studies provide information on how the properties of clay contribute to its strength. By taking a broader view, it is possible that certain types of clay from the region could still be usable, making reuse possible. This would eliminate the need to transport clay from far away. That saves costs and reduces CO2 emissions.
Collaboration
The Noorderzijlvest Water Authority is conducting the 'Clay Erodibility Study' in collaboration with Deltares, Fugro, and Wiertsema & Partners. The Flood Protection Programme (HWBP) subsidises the study.