The geosynthetic systems on slopes are, in most cases, subjected to unfavourable hydraulic conditions. To design these systems, it is therefore necessary to take these conditions into account. A new inclined plane, test procedures and related interpretation methods are proposed here with the objective of providing a more accurate representation of the different situations encountered, in particular wetting of the interfaces and seepage in the protective soil cover. A wet friction angle, generally smaller than the dry friction angle, is defined and the negative role of the water pressure at the slide interface is evaluated. As well as this, a revised version of the standardised procedure is proposed for determining the friction angle when the sliding observed in the course of the test is gradual; this proposal is based on the force necessary to hold back the upper box or the geosynthetic placed immediately above the slide interface. Results are presented to demonstrate the interest of the new types of tests developed.
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