Despite the complicated soil conditions related to coarse alluvial valley deposits, associated with challenging hydraulic flow conditions, the 50m deep cut-off walls on the upstream and downstream sides of the Jannah Dam in Lebanon were finalized in the last days of 2017. The last panel was cast on December, 28^th and the cut-off wall handed over, to the full satisfaction of the client, ahead of the schedule, despite the additional cut-off wall extensions into the fragmented mountain massif on the flanks.