Evaluation of the effect of coefficient of restitution on rockfall analyses using 3-dimensional models

Due to its geological, geomorphological, and climatic characteristics, Türkiye is located in a geography where natural disasters frequently occur. Among these natural disasters, rockfalls cause significant loss of life and property in many parts of Türkiye. In rockfall models, normal restitution (Rn) and tangential restitution (Rt) coefficients are the most important parameters that control rolling distances along with block kinetic energy and velocity. These coefficients determine energy or velocity losses during the block's impact with the slope surface, thus revealing the path and movement dynamics of the block in the model. Restitution coefficients can be determined through field tests (block drop) or retrospective analyses considering the positions of previously fallen blocks in areas where rockfalls have been observed. In cases where restitution coefficients cannot be determined through field tests or retrospective analyses, data from previous scientific studies on similar lithologies or nearby areas can be used. In this study, the effects of restitution coefficients (Rn and Rt), which are significant parameters that can be determined/selected by different methods in rockfall analyses, on rockfall rolling paths, bounce heights, lateral dispersion, and other parameters were evaluated. Three-dimensional rockfall simulations were conducted on a real digital surface model, and the effects of changing Rn and Rt values by specific ratios on the parameters were observed. As a result of the study, it was concluded that changes in normal (Rn) and tangential (Rt) restitution coefficients caused different rates of change in all parameters. When comparing the analysis results, it is understood from the data sets and distribution graphs that the Rt coefficient is more influential on the parameters compared to the Rn coefficient. Increasing the Rt coefficient value, especially beyond values like 0.5-0.6, has been observed to result in significant changes in rolling distance and lateral dispersion.