Three dimensional rockfall analysis and determination of protective measures around Karahıdırlı (Mersin)

Rock mass concept includes rock material and discontinuities. Rock material might be fresh or subjected to varying degrees of alteration. Several types of instabilities are encountered due to the orientation and characteristics of discontinuities within the same mass. Rock fall is the movement of rock blocks formed by discontinuities with different orientations basically because of gravitation. The study area is a disaster prone one, covering some section of Karahıdırlı district of Erdemli, Mersin. Multiple rock falls have taken place in the Mid-Miocene aged reef limestones and no preventive measures have been applied. This study aims to investigate the reasons of rock fall events based on recently developed three dimensional analysis. Digital map of the study area was formed by the orthophoto and point cloud imagery using unmanned aerial vehicle (UAV). Locations of formerly fallen blocks were determined using such imagery. Also the boundaries of source rock mass which includes blocks with rock fall potential were detected during field work. The petrographical determination of the limestones obtained from the sections where blocks are apart from the source rock indicate rock fragments of different origin. No distinctive and reasonable sets of discontinuities were observed in order to characterize the rock mass. Rock blocks with lower unit weight are possibly split by infiltration of water following heavy rainfall. Three dimensional rock fall analyses were carried out taking the dimensions of already fallen/rolled blocks and free blocks within the source rock zone into account. The basic friction angle and unit weight of the geological units were also considered. Necessary precaution methods are evaluated based on the bounce height of the blocks and the location where kinetic energy is dissipated. A steel barrier with 5000 kJ capacity with 100 m length and 5 m height or feinforced earth embankment with 125 m length and 6 m height would prevent the rock falls before reaching the residential area for the east section. The source rock zone on west section is more intact and few already fallen blocks and possible free blocks were observed. Steel mesh with cable nets with anchorage will be sufficient for this section.