River bed and bank protections should be designed regarding unsaturated soil conditions. Natural surface and pore water are not ideal incompressible fluids. Microscopic gas bubbles are dispersed in both of them. Due to the compressibility of such fluids delayed pore water reactions can be observed when external pressure changes act on such a medium. This paper deals with the results of laboratory measurements carried out in a newly built pressure tank. Critical soil areas have been observed through several endoscopes during such pressure changes. In analysing the captured image sequences the local displacement vector fields and structural changes within the soil could be automtically detected by a specially developed image processing technique. Here we concentrate on the description of the employed observational and analytical methods.
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