|M.Sc Thesis||Department of Civil and Environmental Engineering|
|Supervisor:||Assoc. Prof. Talesnick Mark Lloyd|
|Full Thesis text - in Hebrew|
The coefficient of restitution (C.O.R) in rockfall studies serves as an indicator of energy loss during impact as the boulder moves down slope. This coefficient has been defined in two ways in the literature. In the first and more common definition it is separated into two components, perpendicular and tangential to the slope profile. The second definition is based on total kinetic energy, including both the translational and rotational components.
The research has focused on the evaluation of C.O.R for excavated slopes, of geometry similar to that common along roads sides in Israel, i.e., steep slopes with nearly horizontal berms. The research methodology integrated full scale experiments and photographic tracking of boulder trajectories, at three sites located in the lower Galilee. Each site was of different geometry and rock composition ranging from marly chalk, limy chalk, and dolomite.
In many instances the apparent C.O.R evaluated for the impact between the boulder and the steep slope face was greater than 1.0. These results are in contradiction to common theory, despite the fact that such outcomes have been reported upon in the literature. It was found that the energy dissipated during the impact of a boulder with a steep slope is relatively low. Despite the reduction of the velocity at the time of impact, the velocity immediately increases due to gravity, resulting in apparent C.O.R greater than 1.0. It was recognized that the time intervals before and after impact over which these parameters are determined, is of primary importance. No discussion was found in the literature related to this issue. In order to neutralize effects of gravity, linear regression and extrapolation of the velocity ratio was performed; each ratio at a different time interval from impact. Through this process, a decrease in the velocity ratio approaching the moment of impact is apparent. The extrapolation allows determination of the tangential and kinetic energy C.O.R at the exact moment of impact; resulting in values less than 1.0. As for the normal C.O.R, values greater than 1.0 should be considered extraneous.
The research confirms the dependency between the slope angle and the magnitude of the normal C.O.R. The dependency is most clearly noted in the comparison between the high values obtained in steep slopes to low values for the berms. The reason for this difference is felt to be linked to the intensity of the collision, which tends to be much higher at high angles of impact.