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For the construction of a spillway approach channel of the Sandillal Hydropower Dam Project in Costa Rica, a rock slope in vulcanic tuff had to be cut back. Due to unfavourable geological conditions, sliding of the excavated slope occurred. Because the sliding mass in the approach channel had been removed, the slope remained in unstable condition. A retaining berm at the toe of the slope was constructed to stabilize the 40 m high slope. Due to the limited width of the approach channel and hydraulic conditions, the required slope inclination of the berm of lv: L 25h co’uld not be achieved by means of a normal embankment out of the available random fill material. Therefore, a reinforced soil embankment was designed and constructed out of non-woven gotextile. Special shuttering was designed to allow the placing and compaction of the fill in l m layers between the geotextile reinforcement. The geotextile in the slope surface was protected by shotcrete against UV-radiation, atmospheric influences and water action in the spillway approach channel.