The Telleda Tunnel forms part of the high-speed railway line between Barcelona and the French Frontier, precisely in the section between Sant Celoni and Riells. It has a length of 214m and an air section of 85m(2). The uniqueness of this tunnel lies in that it had to be built on a hillside, with completely asymmetric stress conditions in the ground. It was to be dug in soft rock and have very little cover. For the purpose of reducing the environmental impact of the work, a mixed method of construction was planned: combining in cut and cover and underground excavation. The open cut excavation required a provisional slope to be created during the work, with a maximum height of 32 m and a gradient of I (H): 1.5(V), equivalent to 56.3 degrees, which required a very precise soil geomechanical characterization and very accurate numeric modeling to assure its stability during the work. In this paper a description is given of the soil characterization process, the numeric modeling employed and the behavior of the bank during the different phases of the work, which was excellent.