Almonte has become a worldwide point of reference in recent months. The FCC-constructed viaduct attends to the high-speed railway line which spans between Madrid and Extremadura to the Portuguese border. The railway line was constructed by Adif Alta Velocidad and runs between the municipalities of Garrovillas de Alconétar and Santiago del Campo in the province of Cáceres.
The viaduct is divided into three distinct parts: two access roads and one central section. The central section comprises a 384-metre-long concrete arch span. The bridge is 996 metres long with a deck fixed upon a 14-m-wide and 3.10-m-thick statically indeterminate box section formed by 23 spans.
An FCC’s benchmark viaduct
“…railway bridge with the largest reinforced concrete arch span worldwide, stretching 996 metres in length and with a central span of 384 metres.”
The construction of the Almonte Viaduct arch has broken a new world record. Once completed, the viaduct will become the railway bridge with the largest reinforced concrete arch span worldwide, stretching 996 metres in length and with a central span of 384 metres.
“With regard to previous railway projects, both in Spain and within a European and global scope, we are exceeding the record length of what has been built until now by 1.5″, claimed Pedro Cavero, site manager of the Alcántara-Garrovillas Reservoir Joint Venture.
This structure will exceed the Dashegguan bridge in China by 336 metres. Also, amongst those which are used as railways –even if not high-speed ones–, it will also exceed the bridge over the Froschgrund lake in Germany by over 100 metres, also made of concrete, on the Nuremberg-Erfurt line, which is 270 metres long.
If it is only compared with concrete arch bridges, regardless of railway use, it will be the third largest in the world, only behind the Wanxian bridge in China, which is 420 metres long and “very close” to the longest of the bridges between the Sveti Marko and Krk islands in Croatia, which is 390 metres long.
Pablo Jiménez Guijaro, construction manager and area manager of Adif Alta Velocidad, assures that “We are presented with exceptional scales. Each day, we have a new technical challenge to face.”.
Innovation has been prevalent throughout the entire process, serving as a crucial element to successfully construct the arch. David Arribas, head of bridges I department in Technical Services at FCC Construcción, who has led the detail project tells us that “When one takes a leap forward in terms of the scale of projects one carries out, many new things are learnt along the way. In a project of this calibre, any given element of the construction process is innovative”.
The construction process
The project was designed by Arenas y Asociados and IDOM. FCC Construcción Technical Services have been in charge of implementing the detail project, making it possible to carry out the construction process of the viaduct which is adapted to the special conditions of a particularly complex structure.
“It is a particularly lowered arch with a rather unique octagonal shape, even though it is common for arches to be rectangular. The arch begins with two legs which are connected in the middle to become one”, said David Arribas.
Pablo Jiménez Guijarro guarantees that “FCC, as a powerhouse construction company, has provided all of the engineering resources necessary to implement the project. Both the bridge crane system and the definitive system that were used on the cable-stayed tower at the were designed by the FCC technical team”.
During the construction process of the bridge, the construction technique that stands out most was the use of bridge cranes to position segments one by one, as well as to subsequently tighten these by means of cable-stay systems. It is a provisional tightening method which enables each one of the semi-arches until the closing of the arch to be underpinned, after which the bridge becomes free-standing.
David Carnero, head of general production on the project states that “The bridge cranes are motorised and free-standing, functioning as a cantilever and move alone by means of a hydraulic system present both at the lower beam as well at the overhead gantry”, to which Agustín Alonso, head of structural production, adds that “The greatest complication during the assembly of the arch was the fact that it varies a lot”.
Two Major Milestones
Closing of the arch
During the week of 3-7 August, the FCC Construcción team worked on a very complicated operation regarding locking and closing the arch of the Almonte Viaduct with the keystone. This operation came to a close in the early hours of Friday 7 August with the concreting of the last segment.
Lowering of the bridge cranes
On Wednesday 19 August, the process to remove the bridge cranes used to close the arch of the Almonte Viaduct got underway.
The operation consisted of lowering the main beams of the cantilever bridge cranes that were used to execute the North edge of the Almonte arch. It was carried out using a system of 4 HEAVY LIFTING type hydraulic jacks with a synchronised stroke between the 4.
The weight of the part to be lowered was approximately 100 tonnes and the bridge cranes were lowered at a speed of approximately 12 m/h and unloaded into a pontoon, which was chartered specifically to receive the load.
Once this operation is finished, the completed arch in its entirety can be seen without the bridge cranes.
Detensioning and dismantling of the provisional staying system is currently being carried out and pilasters are being put in place which will subsequently support the deck of the viaduct.
Site Manager of the Joint Venture
“The magnitude, geometry and design of the project generate very specific characteristics which present new challenges to overcome”
What are the most significant aspects of this project?
The magnitude, geometry and design of the project generate very specific characteristics such as the variation in the sections, aspects which present new challenges to overcome during each working day.
We have 60,000 cubic metres of all types of concrete, which vary from the most common or regularly used on civil works or in construction, 20 MPa, 30 MPa, to high-pressure concrete, 80 MPa self-compacting concrete for the arch, or 60 MPa concrete on the deck.
Like other significant amounts, we can highlight for example that near to one million kilos of steel are used on the two auxiliary towers of the viaduct which function by tightening the provisional cables which enable the cantilever.
We also have another million kilos of steel in cables and close to 8,000 tonnes, more than 8 million kilos of passive steel, inside the bridge.
“The experience, the team, and the know-how have ensured that previously unaddressed obstacles have been overcome.”
How does FCC contribute to the overall project?
FCC spearheads the construction of this section and exclusively implements the detail project. The experience, the team, and the know-how have ensured that previously unaddressed obstacles have been overcome.
What has been the main challenge?
There is no single challenge. The magnitude of the project we are facing is so large that it brings about new challenges daily that must be resolved.
What repercussions has the know-how of such a unique project as this one had?
“The construction of the viaduct has generated high interest from the academic community as well as from the professional sector.”
The construction of the viaduct has generated high interest from the academic community as well as from the professional sector. We have received visits from practically every engineering school in the country and even internationally such as from Princeton University, whose interest has now led to a video which is currently found on YouTube. Professional associations and companies in the sector have shown a special interest in this project and we have been able to share with them the progress and challenges presented from such a unique project.
How many people have worked on the project?
The construction phase of the semi-arches involved approximately 80 people. The highest number of people involved worked on the simultaneous construction of both the arch and the access decks to the arch, reaching a total of around 170 people on site.
What environmental measures were taken?
In basic terms, it would be necessary to point out two key measures in this regard. We carried out an ornithological tracking of all of the families or pairs of birds which could have been affected during the implementation of this work project; in fact, there was a pair of golden eagles living in this area which were in danger of extinction, therefore we had to make a group of nests so that the pair could nest several kilometres away above the river. We did it. In the end it worked out well.
The other measure was executed through the installation of a “birdlife screen” which functioned by ensuring the birds soared upwards, crossing above the overhead cable so as to avoid colliding neither with the railway nor with the cable.
“The viaduct, as well as the stretch and line incorporated into such, are going to cut transport times”
How is the viaduct going to bring value to the community?
The viaduct, as well as the stretch and line incorporated into such, are going to cut transport times, considering that Extremadura is extremely large regional community. As soon as we have a high-speed system in place, internal journey times are going to be shortened, such as the connection with Madrid, for example. The Cáceres to Madrid journey currently takes approximately 3 hours and a half, and the Badajoz to Madrid connection takes one hour and a half. Both journeys will be reduced by 30 and 50 minutes respectively for services with stops, and by even more for direct or semi-direct services. This is without doubt a remarkably significant advancement.