Fontana Mario

Murgangrückhalt in Wildbächen - Grundlagen zu Planung und Berechnung von flexiblen Barrieren

Project Number: CH-4407

Project Type:	Dissertation
Project Duration:	05/01/2005 - 10/31/2008 project completed
Funding Source:	ETH ,
Project Leader:	Prof. Mario Fontana Institut für Baustatik und Konstruktion ETH - Hönggerberg HIL D 36.1 Stefano-Franscini-Platz 5 8093 Zürich e-Mail: fontana(at)ibk.baug.ethz.ch

related to this project.

for which the project has a relevance.

Research Areas:

Landscape

Disciplines:

engineering sciences
civil engineering

Keywords:
debris flow, large scale test, impact pressure coefficient, flexible protection barrier

Abstract:
In mountainous regions throughout the world, debris flows constitute a threat to human lives and infrastructure. Debris flows are often caused by heavy rainfall. They consist of debris containing mud and coarse sediment that flows downslope towards the valley bottom. This study investigates a new system to provide protection against debris flows, ring net barriers.

Existing approaches to describe the loading induced by debris flows are described in a historical context and their range of application is given. New results from full-scale field tests at the Illgraben debris flow observation station, Canton Valais, Switzerland and scaled laboratory tests led to the development of a new loading approach:
During the stopping process of a debris flow, the hydrostatic load depends on the mass density and the height of the flow. The associated dynamic load depends on the square of the impact velocity, on the density and on a velocity-head pressure coefficient and a flow and material-dependant coefficient. The pressure coefficient values of watery debris flows tend to be smaller than those of granular debris flows where friction is more important. If the first debris flow wave is stopped by the ring-net barrier, the subsequent filling process can be roughly described visually by iteratively fitting the second wave to its flow height over the first one, so that the total pressure distribution on the ring net can be calculated. If the barrier is completely filled, the load approaches that of the active earth pressure state because more water is continually drained from the stopped material due to the extra load from the overflowing debris flow.

Field and laboratory tests have confirmed a new friction relation taking into account the flow process variables involved in debris flows. This law contradicts the common assumption that the Mohr-Coulomb friction relation with a constant friction parameter also describes debris flow friction.

A software tool called FARO, which was originally developed for simulating rock-fall protection systems with flexible ring-net barriers, was adapted for the area loading of impacting debris flows to facilitate calculation of the structural behavior of the barriers. The software tool CARAT is recommended for the form-finding studies of the soft and flexible, membrane-like structure of the barriers. The design of the support structure is not considered herein and should be dimensioned during the planning phase.

First steps for a safety concept should supplement the design of the ring-net barriers in practice. An example is given to illustrate the step-by-step approach to calculation, which is summarized in a flowchart.

Leading questions:
Investigation on a new system to provide protection against debris flows: ring net barriers.

URL: http://e-collection.library.ethz.ch/eserv/eth:30927/eth-30927-01.pdf#search=%22vorgelegt%22

Publications:
Wendeler, C. 2008. Murgangrückhalt in Wildbächen - Grundlagen zu Planung und Berechnung von flexiblen Barrieren. Dissertation. ETH Zürich.
pdf Abstract


Last update: 7/18/17
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