2.
DESCRIPTION OF THE SOLUTION
2.1.
VIADUCT DESCRIPTION
During the study of solutions stage, different options
were studied to cross the river bed, complying with
the environmental impact statement. Finally,
an over-deck concrete arch was chosen to bridge
the Almonte river bed. Once built it will become
the longest railway arch viaduct with a span of 384 m,
and the third longest in the world considering all
concrete arch viaducts for highways and railways, only
surpassed by the Wanxian Viaduct (420m) in China
and KrK I (390 m) in Croatia. In order to support
the deck over the arch, eight piers were located
on the arch at 42 m centres, merging the deck and
the arch in a unique section in the 17 central metres
of the arch. The approach viaducts of the deck
to the edges of the river for each side is arranged with
approaching spans of 45 m until the deck reaches
the main piers over the arch foundations. This way,
a 996 m length viaduct is materialised with a straight
alignment and a slight vertical sag curve with
a parameter of Kv=45.000 m, being the sag point
on the approaching north spans.
In order to improve the behaviour of the arch
resisting transverse forces (mainly wind), the arch is
divided into 2 arms at the springing point, merging
in a single section 87 metres away from the springing,
keeping this configuration over the central 210 m
crown section.
2.2.
CROSS SECTION OF PIERS, ARCH AND DECK
The piers of the viaduct have an octagonal hollow
cross section of variable dimensions and with
a constant wall thickness of 0.40 m, except in
the main piers over the foundations of the arch
(P6 & P15), whose wall thickness is 0.80 m at the
base, and solid from the middle of the pier to the top.
This is necessary to achieve the anchorage
of the 8 first families of temporary stays.
The cross section of the arch is variable in its whole
length, clearly distinguishing two different sections:
a) Double cross section: The arch has double
hexagonal hollow cross section with a variable
depth between 6.90 m and 6.10 m and a variable
wall thickness between 1.07 m and 0.64 m
in the first 87 m from the piers positioned at both
banks. The transverse distance between
the external faces varies between 19 m at the
springing point and 8.37 m where the two legs
merge into a single cross section.
b) Single cross section: In the 210 central metres
of the arch, it has an octagonal hollow cross
section with a variable depth between 6.10 m and
4.80 m in the key, and a variable wall thickness
between 0.97 m and 1.16 m. The width of the
cross section is also variable, decreasing to only
6 m at the crown.
On the other hand, the cross section of the deck is
a typical post-tensioned box with a constant depth
of 3.10 m, and 14 m of width, throughout
the approach spans and the spans over the arch.
As mentioned, the arch and the deck merge into one
combined cross section at the central 17 metres
of the arch.
2.3.
MAIN MEASUREMENTS
The main measurements in the Almonte viaduct
construction are the following:
- Concrete: 60,000 m3
- Reinforcement bars: 8,250 tonne
- Posttension strands: 500 tonne
- Cable Stays: 910 tonne
- Temporary tower steel: 920 tonne
- 2000 kN Ground Anchorages: 6,000 m
- Cement injected to the ground: 530 tonne
Fig. 1. Longitudinal profile of Almonte River
4/2016