3.3.7 Visual data acquisition and image analysis
Digital image processing techniques can be usefully applied to measure the model deformations and displacements during and after the centrifuge tests. Especially image processing techniques are suitable for analyzing the surface deformation in soil models, automatically and in-flight. An acceptable level of accuracy can be obtained using a standard configuration.
Several methods may be used to mark the model surface. Although it is possible to elaborate tests from photographs or film, advanced techniques such as X-ray system or high speed cameras can also be used. These methods are particularly suitable for monitoring the test progress in a centrifuge, since detailed information on the model deformation can be obtained inflight.
For clay models, the soil surface can be marked by grids. Methods have been developed to copy the grid to the clay surface, without the need of removing the boundary. This methods prevents that soft clay samples will be disturbed. For sand models, markers can be used to schematize the surface.
Besides monitoring the surface deformation of the soil, image processing technology can be used for wide area of centrifuge modelling, such as:
1) determining particle size distribution and shape factors 2) displacements in ground water flow, 3) displacement of objects, 4) the spreading of pollution in soil, and 5) photoelastic stress measurement.
It is also true that the application of the image processing technology is not restricted only to centrifuge modelling. Other applications to laboratory tests and field tests can also be possible for the effective use of the system.
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References
Allersma, H.G.B. (1990) : On line measurement of soil deformation in centrifuge tests by means of image processing, 9th Int. Conf. on Experimental Mechanics, Copenhagen, pp. 1739-1748.
Allersma, H.G.B. (1991) : Using image processing in centrifuge research, Proc. of CENTRIFUGE 91, pp. 551-558.
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