ABSTRACT:

Within the framework of the revision of the natural hazard map concerning the area of the villages Schwanden, Hofstetten, Brienz and Brienzwiler in the Bernese Alps assessment and rating for the as-is-state of the 100-years old torrent control structures in the Lammbach rift valley had to be done. This paper shows the general course of action in the project which was done on the basis of the 5 step procedure of the PLANAT. Special boundary conditions concerning the data collection of constructions and subsoil are discussed as well as characteristics of the different torrential barriers. For the visual inspection of the natural stone masonry of the torrent control structures the "Lucerne Rating System" has been used. For the check of the structural safety as well as the fitness for purpose of the structures simple 2D-models have been used just as well as 3D-FEM. Some of the results are presented here.

1 INTRODUCTION

The mountain torrents of the Brienz area are well known for their flooding and debris flows for hundreds of years. In the year 1896 disastrous debris flows occurred in the Lammbach rift valley which destroyed several houses in the village Kienholz, along with the track of the Swiss Federal Railway. The volumes of the last three incidents have been reported as approximately 300,000m3 of material covering land along a shoreline length of 120m with an average debris thickness of about 2.5 to 4.0 m. In consequence of those disastrous debris flows, torrent control measures had been installed in the Lammbach rift valley to raise the streambed and stabilize the slopes. For this purpose 20 barriers had been constructed in the period 1896 to 1913. Those barriers consist of natural stone masonry and have remarkable dimensions in part.

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