GIS-based detachment susceptibility analyses 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 has become necessary to widen the Ankara-Eskisehir (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. The outcomes of the analyses were compared and evaluated with the field observations to check the reliability of the methods and to assess the detachment zones that may develop in the future. The detachment susceptibility map without the block-size layer gives the best result and indicates some risky zones where detachments are likely to occur in the future. Recommendations on remedial measures of the cut slope should consider these risky zones.