Assessment of Rockfall Hazards in Weak Rock Environments and Urban Texture-Compatible Solution Proposals: The Case of Istanbul/Silivri

With population growth, construction in high-risk areas increases, leading to more people and structures being adversely affected. Rockfalls constitute a significant portion of these natural events. However, in combating these disasters, advancing unmanned aerial vehicle (UAV) technologies and three-dimensional rockfall simulations provide highly accurate results in detecting rock blocks with fall potential, identifying hazardous zones in inaccessible slopes, and predicting possible movement trajectories. These technological advancements significantly contribute to field studies, saving considerable time and effort. Rockfalls occurring in the low-strength, Oligo-Miocene sandstone-siltstone-claystone alternation succession on the cliffs of Istanbul-Silivri District cause damage to people and structures along the coast. Additionally, the presence of bird nests on the cliffs affects the design of the reclamation project planned to be carried out in the study area. Within the scope of this study, high-precision mapping was conducted in the study area using RTK (Real Time Kinematic) and PPK (Post-Processed Kinematic) photogrammetric measurement techniques. Consequently, 2.58 cm/pix resolution orthophoto, a point cloud of the study area and 3D stereoscopic optical model of the terrain were produced. Subsequently, an engineering geology study was carried out in the area. Representative samples were collected for laboratory experiments and the orientations of joint systems such as layers, faults etc. were measured. Thin sections of these samples were prepared and petrographic examinations were carried out. Mechanical tests with the index were conducted to obtain the geomechanical parameters of the rock. Afterward, to evaluate the rockfall potential, a kinematic analysis was performed using the DIPS software with discontinuity measurements obtained from the field, revealing the presence of wedge-topple type rockfall potentials in the area. In the second part of the risk assessment, the geomechanical parameters obtained and data from field observations were evaluated collectively to develop an engineering geology model of the study area. This model was integrated with a digital elevation model, and a finite element analysis (FEM) of the slope was conducted using the RS2 program, based on the Hoek-Brown failure criterion. In the final stage, rocks at risk of falling were identified using high-resolution 3D terrain models and field observations. To determine the run-out distance, bounce height, velocity, and total kinetic energy of the falling blocks, three-dimensional rockfall analysis were performed using the RocFall3 software. In conclusion, the risks and hazards in the area were mapped along the cliff with their spatial distributions. Protective structures and remediation methods were then proposed to minimize these risks and hazards.