CENTRIFUGE RESEARCH ON ENVIRONMENTAL GEOTECHNICS
to homepage centrifuge TUDelft).
Orientating tests on capillar behaviour of sand in a centrifuge
The capillar rising of water in a sand column is examined under
increasing gravity. Two sand columns (silver sand (left hand)
and dune sand (right hand))
are placed in the centrifuge. After stabilization of the capillar
rising the image of the setup is stored on disk.
Next the rotation speed of the centrifuge is adjusted at an acceleration
of 9g. The initial and final wetted zone is made visible by subtracting
the images (click here).
Two strange phenomena can be observed.
- The capillar rising at 9g is much more than 1/9 of the height at 1g.
- The difference in rising between the sand types is dissapeared.
Next the gravity is increased up to 18g. The change in capillar
rising is shown in this picture
The comment here is
- Dune sand (right hand side) behaves as expected
- Silver sand seems to be going down more than twice
It seems that the capillar phenomenon at higher gravity
is more complicated than expected in the first instance. A reason of the
behaviour can be found e.g. in the property of the particle surfaces.
If the surface is somewhat fatty a different behaviour can be expected than
when the surface is cleaned e.g. by accid. It appears that the capillar rising
is much more when the sand grains are wetted in advance.
More research is required before final conclusions can be drawn.
The following additional information is given :
- particle size diagram (clic here)
- boundary conditions (clic here)
- observation time until stabilization of the wet surface.
Please see the following data as an indication
DUNE SAND
porosity 67%
averaged saturation wet part (1g) 26%
averaged water content wet part (1g) 21%
SILVER SAND
porosity 68%
averaged saturation wet part (1g) 23%
averaged water content wet part (1g) 19%
The gradient of the water content is not determined. However, this is
in principle good possible, even in a centrifuge test.
Back to previous pages
- Back to Experimental Research
This page has last been edited 12 December 1996 by h.allersma@CT.TUDelft.nl.