Two- and three-dimensional slope stability evaluation in a residential area: Denizkonak landslides in Cide (Kastamonu, NW Turkey)

In this study, it was aimed at evaluating the slope stability conditions in a residential area exposed to two landslides in the past by using two- and three-dimensional limit equilibrium analyses. Two separate, but interdependent, landslides were observed in the investigated area. In 1992 and 1994, two landslides occurred in the region after heavy precipitation and caused damages on the houses and infrastructures. An extensive field work was performed to obtain input parameters for the analyses. In addition, an unmanned aerial vehicle was flown to obtain a three-dimensional view of the landslide area for better understanding of the past failures. The landslides occurred in a flysch-type material representing complex geological characteristics. Hoek–Brown failure criterion and Geological Strength Index were chosen for the strength and visual definition of the geological unit. Since the landslide triggering factor was precipitation, the analyses were focused on the water conditions causing the failure. Sensitivity and back-analyses were performed to obtain the conditions of failure. It was revealed that a high pore pressure ratio was needed to trigger the landslides. However, the second landslide was failed with a lower pore water pressure and the current topography was determined to be on the edge of failure with a slight increase in the pore pressure ratio. In other words, the study area was still found to be prone to possible landslides in the future.