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Stability Analysis of a Rock Slope on the Bristen Road using AutoBlock


About every 10 years major rockfalls occur along a 2 km long section of the Bristen mountain road at the entrance to the Maderaner valley in Switzerland. In 1998 the Institute of Geotechnical Engineering (IGT) of the Swiss Federal Institute of Technology (ETH) Zurich investigated the scale of the hazard this presented together with any necessary remedial measures, in order to guarantee the safety of the road over the coming years. For this purpose all relevant data was collected in a systematic way and a detailed safety analysis was carried out. After executing a fairly large excavation to prevent the seepage of water into the slope, the stability of the exposed roughly 20 m high rock slope under-went a detailed investigation and remedial measures were proposed. The computer program AutoBlock being developed at the time at the abovementioned Institute could be used for his purpose.

AutoBlock allows the stability of rock masses to be systematically investigated in a digital terrain model. To determine potential unstable blocks the terrain model is intersected by a series of discontinuities. The stability is then calculated for each block found. Thanks to the automation and the various presentation and visualiza-tion possibilities extensive analyses and parameter variations can be performed efficiently, which enables the engineer to gain a better understanding of the problems involved.

The investigations carried out showed that the different rock zones could be secured with moderate costs. The proposed measures included among others a grid of anchors as well as drainage boreholes to reduce the water pressure in the joints system.


Bergamin, Stefan and Kolberg, John and Fritz, Pit

Index Terms:

slope; stability; CAD; analysis; Stabilitat; AutoBlock; rock; TunnelingGroup; Bergamin, Stefan; Fritz, Pit; Kolberg, John


The oral presentation has been saved as a movie with sound and a video (20 min. long, 120 MB size).
NB: precondition to view this movie is Powerpoint 2002 or the corresponding Office Animation Runtime Plug-In of Microsoft (if required you will be prompted automatically).

This publication highlights theoretical investigations of the project. However instead of stabilizing the slope, in reality it was just blasted away, which may be watched in this short video.
NB: for watching it you need a later version of Windows Media Player.

Further Information:

Date published: 2004