Author of this short summary:
Gianluca Rebustini
Authors of article: A.R. Fava,
M. Ghidoli, L. Carli, P. Galvanin
Due to its orography, Italy
has a railway network which includes roughly 1460 tunnels, whose
extent is more than 1480 km. Most of them, approximately 800 km, was
built before 1930 so can be considered historical railway tunnels.
Mainly because of their age,
many tunnels require refitting interventions for solving structural
or hydraulic problems, for the adoption of new electrification
standards, for gabarit adjustment or fire protection improvement.
The lack of information about construction methods, material
features and geotechnical conditions represents usually a
challenging problem when refitting of historical tunnels is required.
Since interventions are
specifically related to each single tunnel, it is generally not
possible to set a unique intervention strategy in advance. However
for planning interventions on existing tunnels a design flow
chart, articulated in the following 6 main steps, has been
proposed:
- Step 1: understand the
reasons of the refitting;
- Step 2: collect information
on geometry, structure, geotechnics and stress;
- Step 3: in case of
structural interventions, carry out a back analysis;
- Step 4: develop design
solution considering constructive aspects and site specific
constraints;
- Step 5: carry out structural
analysis and define a monitoring plan;
- Step 6: start of
construction. Monitor the works on site and the efficiency of the
solution over time
This flow chart has been
followed by the engineering company Alpina S.p.A. for refitting the
tunnels Bricchetto and Fey
belonging to the Italian railway network.
Due to a significant increase
of the convergence and the formation of cracks on the lining,
RFI decided to carry out a
structural rehabilitation of Bricchetto Tunnel. After defining the
geological context and the conditions ante-operam through
stress measures and back-analysis, specialist engineers decided
to reinforce the entire section of the tunnel. In
particular, the solution forecast a concrete invert slab having a “U”
shape and the strengthening of the upper portion of the lining
through the installa tion of steel ribs within the masonry and a
final shotcrete layer.
Strengthening of Bricchetto
railway tunnel © www.impresaluiginotari.com
Refitting works of Fey Tunnel
at first consisted only in lowering the rail level for granting
enough space for the installation of the new contact line.
Subsequently, considering the presence of numerous buildings along
the tunnel alignment, RFI decided to apply European standards for
fire protection of existing lining. After a large survey campaign and
a FEM back analysis, it was decided to place a new concrete
slab at the invert and to apply a fire protective sacrificial
layer specifically developed for underground application.
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