Rockfall Mechanisms at the Silivri Cliffs, Istanbul (Türkiye): Assessment and Mitigation

Summary

Abstract

Rockfalls along coastal cliffs are a common phenomenon caused by coastal erosion, heavy rainfall, earthquakes, and various human activities. If these cliffs are close to settlement areas, the associated hazard can quickly become a significant risk to civil life and infrastructure. The Silivri Cliffs are located in the southwestern part Istanbul, Türkiye, average around 40 meters in height and exemplify a densely used shoreline. This area hosts to one of Istanbul's last known breeding colonies of the Lesser Kestrel (Falco naumanni). Since 2014, seven rockfall events have been officially reported along this cliff section. The geological material comprising the Silivri Cliffs consists of Miocene-aged, interbedded sandstone strata deposited within a regressive delta succession. In order to assess the failures in the area, an investigation was initiated with a 3D DEM visualization via photogrammetry using drone imagery. This approach allowed for the assessment of failures in the following discontinuity measurements and basic field tests to characterize the rock mass. Core samples derived from field-collected blocks showed weak layers have an average uniaxial compressive strength of 1.3 MPa and a unit weight of 19.29 kN/m³, while moderately strong layers average 37 MPa strength and 24.73 kN/m³ unit weight. Initial kinematic analyses indicated that cliffs might experience planar sliding, wedge sliding, and toppling failures. Subsequently, joint-network-based 2D FEM analyses in RS2 identified potential failure mechanisms and SRF values under both static and pseudo-static conditions. Additionally, 2D and 3D rockfall analyses using RocFall2 and RocFall3 evaluated factors such as bounce height and total kinetic energy along trajectories. This study examined rockfall mechanisms on the Silivri Cliffs by integrating conventional 2D analyses with advanced 3D numerical simulations. It also assessed possible mitigation strategies tailored to the site’s engineering context, illustrating how geoscientific research can aid multidisciplinary goals, such as protecting a key breeding habitat for the Lesser Kestrel.