Remediation of the geotechnical problems of the Hasankeyf historical area, southeastern Turkey

The castle, palaces and man-made historical and recent cave dwellings of Hasankeyf will be partly flooded by the reservoir of the Ilisu dam which is planned to be constructed over the Tigris River. Hasankeyf is entirely within the Germik formation which is composed of whitish to light gray and/or beige, medium strong, fresh to slightly weathered, thick to very thick bedded, locally massive, almost horizontal or gently dipping silty, sandy limestone. The major geotechnical concerns in the area consist of the possibility of kinematic failure of the foundation of "Little Palace" and the collapse of some of the roofs of the adjacent manmade cave dwellings carved in rock due to insufficient pillar (wall) thicknesses to carry the overburden load. A limit equilibrium analysis of the kinematically unstable planar rock block underlying the foundation of "Little Palace" was performed as a function of the water level in the reservoir. The maximum required anchor force was calculated as approximately 3,000 kN/m which led to a total anchor force of about 42,000 kN for the 14-m-wide slope face of the unstable planar block. The results of the finite element analysis to determine the minimum stable pillar (wall) thickness required between adjacent caves led to a recommendation to apply a steel arch support to one of the adjacent caves at Hasankeyf in case the wall thickness was less than or equal to 0.60 m.