Assessment of the Risky and Hazardous Conditions of Rockfalls in Clayey Limestone with Discontinuity Control Using Integrated Analysis Methods: The Birecik – Halfet Motorway (Şanlıurfa, Türkiye)

Rockfalls are fast-moving, high-energy events that can significantly threaten lives and property, especially in residential areas and near road cuttings. The study area stand along the 350-meters section of the flanks of a main motorway connecting Birecik and Halfet districts of Şanlıurfa (SE Türkiye) where a rockfall happened in 2019. The rockfall area has considerable traffic and is located near the historic Silk Road and breeding sites of the endangered Waldrapp bird, making it both ecologically and culturally significant.

After the 2019 rockfall event, UAV-based surveys were conducted to generate a high-resolution 3D digital terrain model of the slopes. Subsequently, studies covered an application of the Rockfall Hazard Rating System (RHRZ) to evaluate the risk. Studies also include kinematic analysis, numerical analyses and rockfall simulations. In order to determine the rock mass parameters of the Miocene-aged clayey limestones that compose the slopes, discontinuity measurements were conducted as part of engineering geological studies. Additionally, laboratory tests were conducted on block samples collected from the field. The geomechanical measurements revealed that the rock material's unit weight varied between 18.1 and 21.2 kN/m³ and its uniaxial compressive strength varied between 9 and 15 MPa.

The rockfall risk for the stable sections of the slope was found to be 79 according to RHRZ, indicating high risk. All three forms of failure mechanisms; planar, wedge-type, and toppling-type were determined to have the potential to occur after kinematic analysis. Using topographic cross-sections and engineering geological model along the hazardous locations, 2D Finite Element Analysis (FEA) was carried. The rock mass parameters were updated in accordance with the findings of a back-analysis study that evaluated previous rockslope failures and analysis results jointly. The new parameters were used to conduct FEA studies of the slope's hazardous zones. Lastly, a 3D digital terrain model and RocFall3 software were used to create 3D rockfall simulations utilizng rigid body technique. Key rockfall parameters, such as the normal restitution coefficient (Rn) and the dynamic friction (ϕ), were obtained through back-analysis. 3D rockfall simulations provided falling trajectories of the failed blocks, changes in kinetic energy along these trajectories, and the bounce heights.  Based on the data obtained by the above mentioned analysis rockfall potential and risk of the region were identified. Remediation and mitigation techniques were proposed based on these findings.