Part of the proposed route for a new highway between Lattakia and Aleppo in northern Syria crosses a sequence of stiff Pliocene clays. Unusually, for stiff clays, the natural water content is considerably above the plastic limit and it is suggested that this is due to the high proportion of smectite (montmorillonite) being strongly cemented by calcium carbonate. Railway cuttings formed at slopes of 1 on 1.5 have suffered a number of failures within 5 years of completion. Cuttings formed at 1 on 2.5 are presently stable, but, being ungrassed, have suffered severe erosion due to high rainfall intensity and lack of maintenance to drainage works. The long term stable natural slope angle varies between 6° and 10°.
The basis for the choice of the design cutting slope of 1 on 3 and associated erosion protection and drainage provisions are outlined.