SPIDER® Avalanche - Geobrugg AG

SPIDER ® Avalanche
Avalanche prevention installation at San Michele in Val Formazza.
SPIDER ® Avalanche: safe and quick to install
Technical documentation / January 2010

Intervento di stabilizzazione della Valanga San Michele (VB) / documentazione tecnica / gennaio 2010
Avalanche prevention installation at San
Michele in Val Formazza.
SPIDER ® Avalanche: safe and quick to install
Fig.1: Flight-ready equipment at the
loading site
Fig.2: High-level supply using a
transporter bar with three support
uprights and the corresponding netting
2
Work on stabilizing the snow cover was carried out in the area of San Michele,
upstream of the town, on the left-hand snow-line of the Formazza Valley
(province of Verbania). The work carried out adds to a pre-existing installation,
deemed inadequate by the local authority, as the equipment, installed
in the 1990s, showed clear signs of wear.
The planning choice was to add to the existing snow cover stabilization installation
within the detachment area, using structures approved by the Davos
Institute, internationally recognized as the main authority in the fi eld of snowrelated
phenomena. This choice was guided by research into the safety of the
installation, not only in the immediate future, but also in the medium and long
term, given that the structures approved by the Davos Institute have been
tested in the fi eld, and were designed to provide safety and durability.
The system used was Geobrugg’s new “SPIDER ® Avalanche,” a development
of the tried-and-tested Geobrugg avalanche protection system. The new system
is characterized by the replacement of the traditional triangular rope
panels with rectangular panels of netting consisting of spiral rope made up
of pre-stressed steel wires galvanized with aluminum-zinc alloy (GEOBRUGG
SUPERCOATING ® ). This allows for the creation of a netting retention area that
has fewer gaps and is easier and quicker to install as well as helping to keep
costs down during the production phase, thus meaning a lower price for the
end user.
The site for installing the barrier opened on September 5 and closed on October
30 2009. The work was carried out in two separate phases: fi rst the
laying-out and insertion of the anchors, then the installation of the superstructure.
The two phases were separated by a period of inactivity on the site
due to adverse weather and conditions on the site.
During the phase preceding the laying-out, Geobrugg’s Technical Department
worked with the laying company to optimize the laying-out and the number
of supports. The materials for the superstructure arrived on site at the same
time as the start of work, and were therefore available as soon as they were
supplied to the high level by helicopter.
Manufacture and identifi cation by means of data plates made it easier to di-
stinguish the different types of anchor, facilitating their positioning by helicopter
at the correct points on the site. The transporter bar provided for the
helicopter transportation – developed as a result of Geobrugg’s experience in
the high-level working sector – facilitated materials supply operations. Anchor
insertion operations were completed within the timeframes established.

Upon completion of the anchor insertion operations, the superstructure was
prepared at the loading site, located in a car park at the bottom of the valley,
ready for transportation by helicopter. It was possible to carry out the barrier
line pre-assembly operations quickly as the number of connectors required
had been kept to a minimum and the components were easily identifi able,
being countermarked with labels identifying every single item.
The fl ight phases were completed within seven days. A “typical day” schedu-
led the presence of the helicopter for around one hour early in the morning,
after which linking and bolting of the clamps and chains was carried out. At
the end of the seven days of fl ying, the barrier lines (twelve in total) had been
completed.
The work on the site was then completed within 54 consecutive calendar days,
including days affected by bad weather and some interruptions to the fl ying
operations due to excessive wind.
GEOBRUGG SPIDER ® Avalanche System
Type of avalanche protection Dk 3.0 - N 2.5
Total linear meters 384 m
Number of lines 12
Height of struts 4 m
Days of helicopter transportation 7 days
Total days on site 54 days
Days spent on foundations 47 days
Length of mountain-side anchors 5 m
Length of valley-side anchors 4 m
Length of strut underpinning 3 m
Days spent on superstructure 7 days
Daily rate of installation of super-structure 55 m / day
Fig.3 + 4: Completed barriers
Table 1: summary of the main site data
3

Geobrugg protects people and infrastructures from the
forces of nature
It is the task of our engineers and partners to analyze the problem
together with you in detail and then, together with local consultants,
to present solutions. Painstaking planning is not the only thing you
can expect from us, however; since we have our own production
plants on three continents, we can offer not only short delivery paths
and times, but also optimal local customer service. With a view towards
a trouble-free execution, we deliver preassembled and clearly
identifi ed system components right to the construction site. There
we provide support, if desired, including technical support – from
installation right on up until acceptance of the structure.
Rockfall barriers
Rockfall drapes
Slope stabilization systems
Debris fl ow barriers
Avalanche prevention structures
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Geobrugg AG
Geohazard Solutions
Aachstrasse 11 • CH-8590 Romanshorn • Switzerland
Phone +41 71 466 81 55 • Fax +41 71 466 81 50
www.geobrugg.com • info@geobrugg.com
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