Simple experiments for complex mechanisms

 


We study simple science experiments to understand pressure variation of a fluid when particles are moving upwards and downwards inside the fluid.



By means of a simple experiment, we will measure the fluid pressure and explain the interaction between the grains and the fluid. 

 
I have the pleasure to meet the scientist Othmar Buser. Othmar, currently retired, began working at SLF in 1965 for Snow and Avalanche group. 

Mattertal (Valais, Switzerland): Beauty and the Beast

The Mattertal Valley is surrounded by the highest mountains of the Alps Swiss, like the Dom (4,545 meters) and the Weisshorn (4505 meters).

It is an idyllic place to get a real taste of the natural beauty of the Alps. 

However, the sublime peace and beauty have often struck by the "beast", mass movements (avalanches, rockfalls, landslides and debris flows) over the course of centuries.

Mountain torrent Dorfbach, Mattertal Valais (Switzerland)

In recent years, the risk of these natural hazards seems to have increased likely due to a warmer climate. The glacier retreat and permafrost melting leaves instable rocks and soil. As the permafrost degrades, the risk of unlocking larger amount of rock debris and soil dowslope increases.  Heavy rainfall or snow melt  could provide the trigger of these natural mass movements, in particular debris flows.

Research activities are carrying on in Mattertal to full understand the debris flow mechanisms from initiation, motion and deposition (Hazard mapping in Mattertal VS: Data acquisition and numerical modeling of debris flows) by SLF-WSL. This is crucial to be able to predict potential debris flow activities and hazard zonation mapping for the protection of life and property.

During spring-summer last year two events occurred. The first one, 7^th June 2010, took place without precipitation. In this case the trigger was the water coming from melted snow and ice from the very active rock glacier "Grabengufer". The second event, on the 14^th August 2010, unlike, the first rainfall was the trigger. In both events, burst in pulses were observed in the form of intermittent successive waves of different sizes with varying water and solids content.

The most recent event began on the 4^th June 2011 from rainfall before and during the event.

The debris flow volume from these events varied from 1,000 to 10,000 cubic meters, with velocities of a few meters per second.

The mountain torrent Dorbach (Randa, Mattertal Valais) is located at a debris flow monotoring station. The station encompasses geophones used for seismic data acquisition and as a trigger of the other measurement devices (video camera for visual information, radar for the flow depth and a laser scanner to measure profiles of the torrent geometry which is currently significantly changing).

Radar

Camera

Geophone on the rock

Fix laser scanner

I went to Mattertal Valley with part of Perry's group (from SLF and WSL) to collaborate in the current project by taking some measurements with portable equipments. We have used GPS technology to collect field data, a laser rangefinder and a laser scanner.

Davos: "The Magic Mountain"

Davos, a city way up in the mountains at 1,560 metres is located on the Landwasser River, in the Swiss Alps (East of Switzerland).

Debris flow mitigation measurement in Davos.
The debris retention dams allow smaller sized particles to pass through downstream, while the large boulders with high destructive potential are retained. This is also designed to keep a  healthy  riverine environment.

From my desk at SLF

First week of June at SLF

WSL Institute for Snow and Avalanche Research SLF

It is not as white as the first time I have been at SLF but it has not lost its charm and delightfulness at all...

Straight away I felt a part of the group again. In our first meeting we discussed the new experiment device and how we are going to perform a set of experiments starting from the physic concept of pore pressure. We exchanged  interesting papers which will be very useful to consider for our experiments.

The atmosphere is great and relaxing. The meetings are from "formal meetings" to "technical chats" during coffee time or at lunch...

I had the chance to share my knowledge and previous experiences in particular my work at the University of Nottingham (Civil Engineering). From the first day at SLF it has been a two-way process. While discussing the experimental facilities, measurement methods used and how to assess the flow behaviour,  I also learned ways to overcome or improve some difficulties of my experiments. I had good explanations in different fields (calculations, physics, instrumentation).

Set-up experiment at Nottingham, UK.

Two-phase flows experiments

We are going to use the collected data from my experiments at Nottingham (two phase flows experiments) and to compare it with their experiment data of dry flows (one phase flows). Another one of our objectives is to analyze the experiment data to verify simple flow models.

Louis Bugnion at the workshop laboratories of SLF is fitting two force plates into the debris chute in order to measure the shear and normal forces at the bed surface for dry flow experiments. We discussed the difficulties of taking the different required measurements during the experiments.


Other issues that we commented:

• Chute design
• Roughness surface
• Lagrangian / Eulerian description
• Velocity profiles - pattern matching algorithm

Avalanches, debris flows and rockfall group at SLF - Davos (Switzerland)

Back to February 2011: the first time I met the "dynamic" Avalanches, Debris flows and Rockfalls Group at SLF in Davos (Switzerland).  During my first week Dr. Perry Bartelt (head of research unit) introduced me to the debris flow team and the SLF facilities. I had the chance to discuss about the develop future work during two months in June and July 2011 at SLF. We confined as our main goal was to perform a set of experiments in two phase flows to understand the physics of the debris flow. We want to take a look inside the debris flow...

This meeting in February was essential to be able to have enough time to design the experiment and order  new measurement materials which was required.