A cut slope in a motorway in northern Spain was excavated in clay shales. The rock structure was a series of consecutive synclines and anticlines, with the axes oriented transversely to the slope. This was considered favourable in the design. However, upon excavation, a slight inclination of the folding axes was evident, inducing a failure, facilitated also by the water flow. The failure threatened a group of houses located near the crest. The sliding area was heavily instrumented with inclinometers. This allowed for a precise definition of the failure surface. Corrective measures included overexcavation at the crest, shallow and deep drainage, an anchored wall at the toe and an anchored pile wall at the crest to protect the nearby buildings. The effectiveness of all these measures was analyzed by means of limit equilibrium calculations.