Debris Flow & Shallow Landslide Protection LENK, BERNESE ALPS, CH
LENK, BERNESE ALPS Debris Flow & Shallow Landslide Protection Project Lenk, Bernese Alps Zip code 3775 Place Lenk Seiten Country/Region Switzerland Year of installation 2017 Customer Engineering Contractor Other participating companies Community of Lenk Emch+Berger AG Bern Steiger Ingenieure + Planer AG Burn & Künzi AG Situation The village of Lenk in Simmental valley (Bernese Oberland) was already affected by debris flows in the past. For example, mudflows in summer 1930 from side streams clogged the bed of the river Simme what caused a deluge in the village. Access to this mountain village - street and rail - was also blocked. During this large event, the quantity of debris flow was estimated as 135'000 m³. Many other minor to medium events were observed in the following decades. After a flood in 2005 (with minor damage), the danger map was revised and the present project was launched. The origin of the debris flow mobilization area is mainly a slump in the Bühlgraben as well as the strong gut erosion of the alluvial soils below it. The catchment area covers an area of around 20 km². It is assumed that the debris flows occur in several discharges. The location of the barrier is at the end of a winding stream. Based on a 3D debris modeling (RAMMS DEBRIS FLOW, carried out by Emch + Berger AG from Bern), the input parameters for the dimensioning flexible barriers were obtained. The final solution is dimensioned with a retaining capacity of 70'000 m³ (in four to five bays of 15'000 m³ each) and flow velocities up to 9 m/s. Debris Flow & Shallow Landslide Protection Lenk, Bernese Alps, CH 2/8
Description To prevent medium size debris flows reach the riverbed of the Simme, a restraint system for sludge and driftwood was created in geologically very demanding terrain. The annual normal water discharge with smaller solid particles can easily pass through the basal opening. Due to the required spans and the specified loads, a design with concrete slabs was chosen. For this purpose, Geobrugg dimensioned the nets and ropes between the concrete slabs (based on the Geobrugg standard barrier VX160-H6). The design of the concrete slabs was developed by Emch + Berger AG Bern. The six foundations of the concrete slabs were securely deeply seated using 15 m deep reinforced pails. Nevertheless, in the case of a major event, this retention volume could be exceeded. Then the remaining debris material passes via the overflow section in the middle of the barrier. Protected object Systems Road, Railway, Building, Touristic infrastructure, Residential area, Infrastructure, Other Special Solutions Corrosion protection GEOBRUGG SUPERCOATING System height System length 5.0 m, 7.0 m, 10.0 m, 12.0 m 40 m - 40 m Number of barriers 1 Retention capacity 40000 m³ Debris Flow & Shallow Landslide Protection Lenk, Bernese Alps, CH 3/8
The custom designed debris flow barrier based on Geobrugg's technology of flexible barriers Flood from 1930 - the village of Lenk in the Bernese alps was completely under water. Afterdebris flows, the Simme river bed was blocked and the village remained flooded for several weeks Overview of the debris flow accumulation area above the village Debris Flow & Shallow Landslide Protection Lenk, Bernese Alps, CH 4/8
Accumulation area and the barrier localization (red). Source: swisstopo, 2017 Concrete pillars foundation during installation - visible huge scale of the project Another view of the concrete pillars foundation during installation - totally ca. 130 m³ of concrete were used. The stream water was by-passed using a temporary piping (black pipe visible on the left) Debris Flow & Shallow Landslide Protection Lenk, Bernese Alps, CH 5/8
Concrete pillars foundation during installation - view from the top. Walls of the deep cut are stabilized with anchored retaining walls View of the almost finished barrier with rock blocks covering the winglet area of the barrier. That solution perfectly covers heavy concrete foundations and prevents erosion during the event To provide extra protection for the concrete pillars, they are covered with tree trunks (easy and cheap in maintenance) Also visible Geobrugg's brake rings, which absorb a large part of the impact energy. Debris Flow & Shallow Landslide Protection Lenk, Bernese Alps, CH 6/8
Side view of this exceptional protective installation in the Bernese Alps. Overview towards the valley - people standing on the right show the enormous size of the barrier equipped with Geobrugg's technology View from below the huge protective structure in the Bernese alps Debris Flow & Shallow Landslide Protection Lenk, Bernese Alps, CH 7/8
For questions please contact our Geobrugg specialist at your side Roger Moor Ost- und Zentralschweiz, Liechtenstein - Country Manager Phone 071 466 81 52 Mobile 078 783 46 81 Roger.Moor@geobrugg.com Geobrugg AG Aachstrasse 11 8590 Romanshorn Switzerland info@geobrugg.com www.geobrugg.com A company of the BRUGG Group Certified to ISO 9001 Debris Flow & Shallow Landslide Protection Lenk, Bernese Alps, CH 8/8