George Tsiambaos

Empirical Model for Predicting Rockfall Trajectory Direction

A methodology for the experimental investigation of rockfall in three-dimensional space is presented in this paper, aiming to assist on-going research of the complexity of a block’s response to impact during a rockfall. An extended laboratory investigation was conducted, consisting of 590 tests with cubical and spherical blocks made of an artificial material. The effects of shape, slope angle and the deviation of the post-impact trajectory are examined as a function of the pre-impact trajectory direction. Additionally, an empirical model is proposed that estimates the deviation of the post-impact trajectory as a function of the pre-impact trajectory with respect to the slope surface and the slope angle. This empirical model is validated by 192 small-scale field tests, which are also presented in this paper. Some important aspects of the three-dimensional nature of rockfall phenomena are highlighted that have been hitherto neglected. The 3D space data provided in this study are suitable for the calibration and verification of rockfall analysis software that has become increasingly popular in design practice.

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.

Effect of Forest Presence on Rockfall Trajectory. An Example from Greece

The impact of falling rocks on human activities can be hindered using protection measures such as rockfall barriers, embankments and other passive structures but also through the presence of forests. In order to study the effect of a forest on rockfall trajectory, a site neighboring a village in Central Greece was selected which has a well-recorded rockfall history in the last 50 years. The village is limited by a relatively dense forest, which lies on a limestone scree slope. An assessment of the role played by the forest stands on the site was done using the Energy Line Angle concept and conclusions on the residual rockfall risk on houses are drawn.