Direct visualisation of underwater phenomena in soil-fluid interaction and analysis of the effects of an ambient pressure drop on unsaturated media

A description is given of an apparatus in which a wide range of hydraulic conditions can be realised. A unique observation system using optical fibre based ‘endoscopes’ and an imaging system that includes a signficant digital processing element enables the visualisation of grain and fluid motion as well as air bubble behaviour in granular deposits of specified composition and geometry under externally imposed hydraulic conditions. Examples are given and a particular application in which a soil is studied that is fluidized by an external pressure drop. A description of the fluidized behaviour is given and the outcomes are cast in terms of a mathematical/physical model for fluidized material. This model is then used to predict the extent of a fluidized region in a one-dimensional situation