Motorway E80 in South East Serbia, connecting Nis and Dimitrovgrad at the borders with Bulgaria, passes through the mountainous region of Dry Mountain (Suva Planina). The design foresees large scale cuttings along a 7km segment, prevailingly within a mixture of generally soft rock formations, including fine sandstones, claystones, siltstones and shales of Permian age. Almost all of the excavated cuttings suffered either limited and local, though progressively expanding instabilities, or global sliding failures. The critical role of the behaviour of the chaotic formation in terms of composition, weathering, structure, stratigraphy and groundwater regime was identified and the mechanisms leading to deterioration of the rock mass were explored. A methodology based on engineering geological mapping and GSI classification, in combination with in situ and laboratory testing, was implemented for evaluation of ground conditions, to establish a rational framework for the design of the rehabilitation measures