Rockfalls: Effect of Slope Surface Weathering on the Coefficients of Restitution

Rockfalls have disastrous consequences on human activities; therefore their study is necessary in order to design effective protection measures. The design of mitigation measures (barriers etc.) is based on trajectory analyses, which depend, amongst other parameters, on the coefficients of restitution. These describe the response of a block to an impact with the slope and are often considered only a function of the falling rock. In the present study, laboratory tests were performed in order to examine the effect of weathering of the slope’s surface on the value of the coefficients of restitution. Samples from Athens schist with different weathering grades were used and the falling blocks were cast spheres made of high-strength cement grout. The incidence angles varied between 20o and 90o. The coefficients of restitution were determined for each test using a high-speed camera and a specialized machine vision computer code developed in Matlab. The values of the kinematic coefficient of restitution were found to decrease with increasing weathering degree. The kinematic coefficient of restitution is preferable for use in rockfall trajectory analysis since no correlation between the normal or tangential coefficients of restitution and weathering of the surface were found.