The increasing population and demand on housing increases the interaction of geo-environment and human settlements. Thus, the rate of natural events effecting daily human life surges for highly populated areas. A rock fall event occurred in a highly populated area in İstanbul (Türkiye) which is also remarkable by its location with many precious historical buildings along the Bosporus strait. The rock blocks belonging to the Paleozoic sequence of İstanbul composed of nodular limestone with sandy-clay interlayers slided and fall a day after heavy rains. The study initiated by the examination of the dimensions of rock blocks and their paths. Simultaneously field study along the source area included investigation of discontinuity properties and weathering properties. Geomatic studies established a very detailed numerical 3D view of the area based on highly precise drone views. These studies also identified potential rock blocks to be detached.
Field observations basically showed the effect of the growing roots of trees within discontinuities. This biologically initiated weathering effect transforms into a physical effect and exert stresses on the rocks surrounded by discontinuities. Laboratory studies showed that the rock has moderate uniaxial compressive strength (40-51MPa) and having kinematic admissibility in some areas due to principal discontinuity sets with rough surfaces (JRC 6-8). Numerical models obtained from various cross sections utilizing field and laboratory data demonstrate the most critical sections to be considered and reinforced. Engineering geological model including weathering and discontinuity properties was also employed at this stage. Considering all the data and results, study advices pre-cleaning of risky blocks after a fence production on the potential falling paths, rock anchors in some localities with varying lengths and a careful drying process on some trees with long root patterns. These mitigation processes were then re-assessed with numerical models showing that the factor of safety increased to desired levels.