Test/preparation techniques, used in centrifuge modelling of the University of Delft.
Making markers on sand surface.
In two dimensional tests on sand there is a need to
monitor the displacement of a surface behind a transparent
wall. An advanced technique is available which uses the local
grain structure to determine the surface deformation.
However, in most cases it is prefered
to make markers at the sand surface, so that the displacements
can be visualized by comparing video exposures of two stages.
-Horizontal grid lines can be made during preparation with black
coulored sand. The model has to be built up layer by layer. After a
pre-defined thickness, a thin layer of black sand is poured. In
principle layers only close to the transparent boundary are necessary.
However, this technique can also be used to look inside a sand body.
In this case the black layers are poured over the whole surface. After
the test has been performed the sand is partly saturated. Thanks to
capillary suction three dimensional cuts can be made in the sample.
- Gridlines can be made with paint in the case the transparent wall
can be removed, and the area to be painted is in the horizontal plane.
A raster with square holes can be used and black paint (spray). The
result is a light colored grid on a black background. Also light emitting
paint (with black light) can be used.
- Good results with point markers are obtained using beads or small
nails (l=12mm) with flat head (d=4mm). In both cases the markers are glued
at the transparent wall with vaseline (eventually a template can be usd
to obtain a regular raster) next the sand is poured into the model box.
Use of batteries in the centrifuge
It is found that dry batteries resist
a g level of at least 150g. There is not
yet experience with fluid filled led batteries.
