EXPERIMENTAL RESEARCH IN GEOTECHNICS

Centrifuge facility of the University of Delft (photograph, movie).

Failure of dikes by overburden pore water pressure (Delft Cluster)

- A centrifuge test program has been carried out to investigate the behaviour of dikes during rising of the water level. It is assumed in this case that the clay dike is founded on a permeable layer of sand. The increasing water level is supposed to increase the pore water pressure in the sand. The pore pressure causes an uplift force at the bottom of the profile of the clay dike. Thanks to friction reduction failure can be triggered.
In order to have a good control over the pore water pressure the pressure under the clay dike can be adjusted by a computer controlled pressure supply system. In the test setup shown in this diagram the pore water pressure can be increased uniformly in the sand layer underneath the embankment. In the diagram shown here it is possible to create a pressure gradient in the sand layer underneath the clay layer. The pump is activated by the on-board computer, using the output of one of the pressure sensors.
In order to be able to perform tests at gravities up to 150g a pumping system has been developed of which the operation is more ore less independent of the gravity.
A photograph of a typical test result is presented here. At low pore pressure a shear band is formed starting at the toe of the dike. Reduction of the friction by increasing pore pressure causes deeper shear bands.
In this movie it can be seen that both mechanisms take place almost at the same moment. In this movie a test is shown where the slope is stabilized by a berm. Furthermore an imperfection is made in the clay behind the dike. A similar mechanism is now realized as assumed in calculations.
This detail shows that a complex shear band pattern can be formed.

Geotechnical Laboratory TUDelft

This page has last been edited December 2000 by h.allersma@CT.TUDelft.nl.