Failure and mobilization analysis of mid-magnitude rockfalls on a steep limestone slope in the Bavarian Alps

Rockfall events pose a high risk to infrastructure like railways or highways, as has been demonstrated by certain events, like in Gurtnellen at 5th of June in 2012 with one casualty. To contribute to an enhanced hazard assessment above infrastructure it is necessary to perform a detailed process analysis. By using current rock fall codes, like Rockyfor 3D or STONE 3D it is possible to perform run out analysis, but with no regard to the failure process at the source area. Therefore we suggest an extensive failure analysis of the source area, taking the joint sets and their shear parameters, into account. We address our contribution at a project site above the federal road B 305 in the Bavarian Alps, approximately 30 km south west of the city of Salzburg, between the villages Unterjettenberg and Schwarzbachwacht. For our key-object of the study, a 200 m3 block subjected to planar failure, we performed a detailed mapping of the detachment surface (which is directly accessible) as well as a quantitative determination of the shear parameters like the joint roughness coefficient (JRC) and the joint compressive strength (JCS). We generated mechanical approach to characterize the failure mechanism of the block based on detailed field reconnaissance. In this contribution, we aim to demonstrate an effective methodology of generating reproducible geological, geotechnical data to yield an enhanced reconnaissance of mid magnitude rockfalls endangering vulnerable infrastructure. .