The design of geotextile filters for granular soils

The use of geotextile filters is very common in geotechnical and in environmental engineering. In these structures the flow conditions (steady and unsteady flow, parallel or normal flow to filter, high or low hydraulic gradients) and the boundary conditions (vertical effective stresses, continuity of contact between the filter and the base soil) can be very different. In all applications the functions of filter are to prevent the movement of fine particles of base soil and to avoid the development of excessive pore water pressure on interface between base soil and filter. The main filter functions are retaining the base soil: pore size distribution and filtration opening size must be lower than fixed limits (retention criterion); being more permeable than base soil: pore size distribution and filtration opening size must be higher than fixed limits (permeability criterion). The available design criteria are often the result of theoretical and experimental analyses carried out in laboratory under experimental conditions different respect to the field conditions. Moreover, the design criteria do not consider the different flow conditions and the boundary conditions. In this paper, on the base of the current knowledge and trends in geotextile filter design and research a new procedure for the design of geotextile filter is shown