The rearrangement of the soil in contact with a geotextile is of basic importance in the behavior of engineering filtration systems. The paper presents a microscopic method for the analysis of soil/geotextile systems. This method supports filtration tests to explain experimental and field behaviors. A morphometric method was applied to analyze the used geotextiles and the microstructure of the soil layer upstream of the filters. In order to observe the natural filter structure and the clogging level of the filter, soil/geotextile samples were encapsulated in an epoxy resin, cross-sectioned, and analyzed under a microscope. The filtration laboratory tests have been performed on in situ soils to supplement microscopic analysis to forecast filtration behavior of geotextiles. Using both techniques, the time-dependent phenomena taking place at the soil/geotextile interface and the clogging mechanisms can be identified. In this paper, the microphotographs of soil/geotextile systems and their water permeabilities as a function of filtration time are presented.