Within the -context of stabilization works in mountainous regions, kilometers of trench drains are constructed each years in the Alpes. These trench drains are filled with clean gravels and are protected from the fill-in (clogging) of the site soil by means of a geotextile filter. An investigation campaign was started in order to analyse the behavior of the filter and of the trench drain. The methodology used and the first results are presented: – following up the behavio ‘.of two ten years old trench drains of about 4 m depth: piezometers have been bored and the water flow has been measured;
– opening and observations of six years old trench drains (1.3 and 1.7 m depth) with or without a geotextile filter. The role of the geotextile and the influence of t e contact between the soil and the non-woven filter are shown.