Assessment of degradation and stability of a cut slope in limestone, Ankara-Turkey

Due to the rapidly growing population of the city of Ankara (Turkey) and increased traffic congestion, it becomes necessary to widen the Ankara-Eskişehir (E-90) highway, connecting the newly built areas west of the city to the city center. During widening, several cut slopes were formed along the highway route. As a result, some instability problems (small-sized rock falls/sliding, sloughing, raveling) produced detachment zones along a cut slope in highly jointed, folded and sheared limestone, causing local degradation of the cut slope. Identification of the areas that are likely to detach from the cut slope in the future is considered to be very important for the application of remedial measures. For this purpose, the relationships between the existing detachment zones and various parameters (e.g. point load strength index, weathering, block size, daylighting, shear zone) were investigated using GIS-based statistical detachment susceptibility analyses in order to predict the further aerial extension of the detachment zones with time. During the overlay analyses, statistical index and weighting factor methods were used. Limit equilibrium analyses were also carried out for the determination of the possible large scale mass failures. The detachment susceptibility map using Wi method without the block size layer gives the best result and indicates some hazardous zones where detachments are likely to occur in the future. On the other hand, the limit equilibrium analysis of the rock mass using Bishop simplified method shows that except one section no mass failure is expected in the cut slope. Suitable remediation measures which include the use of wire mesh, shotcrete, toe support, and concrete barrier blocks or catch/barrier fences are recommended for these zones.