Rockslide mechanics reconstruction using FEM and photoplastic modelling

On a steep eastern slope under a Celtic site of Obří Hrad in the Šumava Mts. (South Bohemia), a complex, multi-generation rockslide was identified. Detailed mapping of the site revealed several systems of rockslide scarps, corresponding to respective deformation generations. Following research was aimed to assess the current behaviour of the slope and likely mechanics of the rockslide. Reconstruction was difficult as the rockslides were not very fresh, and the accumulations were practically removed by the fluvial processes from the narrow valley floor. Numerous research methods were applied. The depth and profile of the potentially unstable slope was investigated using geophysical methods. Several monitoring systems to assess the current movements were installed, including automatic extensometers, rod dilatometers and steel tape extensometers. Detailed measurements of tectonic joints and foliation structures were performed to investigate geometrical predispositions for sliding. Relative dating of the scarps was performed using the Schmidthammer test, comparing the scarps to other exposed rocks. Based on these analyses, a hypothesis on the rockslide formation and mechanics was formulated and tested using two independent methods: FEM calculations in the FLAC software, and photoplastic models, simulating the behaviour of the tectonically fractured rock massif. The preliminary results of these techniques illustrate the possible mechanics of the sliding while the monitoring systems offer a frame for the timescale of the events.