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Assessment of degradation mechanism and stability of a cut slope in jointed and sheared limestone along Ankara-Eskişehir E90 highway

Öztekin, Burak
Due to rapidly growing population of Ankara city (Turkey) and traffic load, it is required to widen some of the existing highways. One of them is Ankara-Eskisehir (E-90) highway that connects highly populated areas to the city center. During widening, several cut slopes were formed along the highway route. However, some instability problems such as small-sized rock falls and rock detachments have occurred along a cut slope in highly jointed, folded and sheared limestone. They caused local degradation of the cut slope. The cut slope has a slope angle varying from 71° to 84° and contains several shear zones. In this study, the relationships between the existing detachment zones and various parameters (e.g. block size, point load strength index, weathering, shear zone, daylight zone) considered to be important for slope instability were investigated using GIS-based statistical landslide 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 by means of TNT-MIPS software. The outcomes of the analyses using both methods are compared and evaluated together with the field observations to check the reliability of the methods and to assess the detachment zones that may develop in the future. Additionally, limit equilibrium analyses were also carried out for the determination of the possible large scale mass failures. The overlay analyses indicate some risky 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