The junction of the deck
 
 
HomeUnderstandConstruction in six stages

Construction in six stages

Six unusual stages of the viaduct construction

A monumental structure built in barely three years... the result of perfect coordination of teams and techniques! 
The Millau Viaduct, at 2,460 metres long, is an essential link in the motorway connecting Clermont-Ferrand to Béziers, which opens up an entire region.

The structure, conceived by engineer Michel Virlogeux and designed by architect Sir Norman Foster, was constructed by the Eiffage Group, which specialises in civil engineering and steel construction.

Most of the cutting-edge techniques used in public works were employed in the construction of the viaduct: lasers, GPS, translation mechanisms, self-climbing formwork, special asphalt, high-performance concrete and innovative materials have made completion of this extraordinary structure possible.

Construction of an extraordinary structure

The Millau Viaduct is the culmination of an incredible journey. From conception to completion, several thousand people united their energy and ingenuity to participate in this unique endeavour.

At the peak of construction, nearly 600 workers were working on the site. They mastered the most advanced technologies to guide the construction of this giant of steel and concrete, with millimetre precision.

Achieving that only took three years, from December 2001 to December 2004.

 

March 2002 / December 2003 – Erecting the piers

The Millau Viaduct has seven piers that support the viaduct deck.

The foundations

From March 2002, just few weeks after the start of construction, the piers began to rise up.
The abutments were built at the same time as the piers, on the Causse du Larzac and the Causse Rouge. On 9 December 2003, a few weeks ahead of schedule, the piers and abutments were finished.

Eiffage met the challenge, with the bonus of the world record for the highest pier, "P2". 

 

20 months to assemble 36,000 tonnes of steel: launching the deck

Two open construction sites were set up behind the abutments, to the north and south of the viaduct. All welding and assembly work was carried out there, limiting the risks associated with working at great heights.

Noteworthy features / Key figures

  • Transporting parts: the heavy transport vehicles, with a height of 4.2 metres and a length of 15 to 22 metres, weighed up to 90 tonnes.
  • The deck is 32-metres wide, while its total mass is around 36,000 tonnes.
  • 20 months of work were needed for 150 workers to build the deck.
  • 96% of the tasks were carried out at ground level.

Launching: the deck hanging in the void

Getting the steel deck onto the piers involved a special launching technique. Section after section (each a half-span in length), the deck was launched into the void.

To succeed in this operation, translation mechanisms were installed on the piers and temporary piers (gigantic steel props serving as intermediate supports between two piers). They thus allowed the deck's 36,000 t to be moved.

At a rate of one operation every four weeks, it took eighteen launches to put both sides of the deck into place directly over the Tarn. Carried out at an average speed of 9 m/h, each launch required up to 48 hours of non-stop work. The deck was joined on 28 May 2004 at 2:12 p.m. above the Tarn.

Noteworthy features / Key figures

  • 64 translation mechanisms to move 36,000 tonnes
  • 18 launches lasting a maximum of 48 hours each, non-stop
  • Average speed of movement: 9 m/h
 

28 May 2004 – Joining the deck

The meeting of the southern and northern decks took place on 28 May 2004, 270 m above the Tarn.

The culmination of 15 months of work was a moment of intense emotion.

A remarkably accurate joining operation!

 

Installation of the pylons – An operation completed in just three months

The pylons continue the line of the piers, above the deck.

The pylons were transported onto the deck by four articulated lorries, in a horizontal position.
In the firm grasp of huge steel arms, they were set upright directly over the concrete piers.

Pylons: Seven steel masts for a viaduct

At the start of the launching operations, a partially stayed pylon was positioned at the end of each deck length to avoid the deck bending when launched between one pier and the next.

Erection of the other five pylons began just after the two parts of the deck were joined above the Tarn. This operation was completed in only three months.

During these operations, a perfectly controlled support tower helped swing the pylons into a vertical position, just above their anchor point. They were then welded to the deck.

Noteworthy features / Key figures

  • Each pylon weighs 700 t and measures 87 m
  • Erecting the pylons only took three months
 

Attaching the stays – 1,500 tonnes of high-tension cables

The stays were installed using a well-established technique. After feeding an initial strand through the protective outer enclosure, the enclosure was hoisted onto the pylon into its permanent position.

The strand was then attached to its upper and lower anchors. A "shuttle" was then used to bring all the other strands in one by one, which were then tensioned.

Key figures:

  • The longest stay is 180 metres and weighs 25 tonnes
  • The tension of the stays is between 900 and 1,200 tonnes
 

Remarkable construction right up to the finishing touches

10,000 tonnes of asphalt laid in less than 4 days

Surfacing of the Millau Viaduct deck was carried out from 21 to 24 September 2004.
Smooth and without a wrinkle, it covers the steel to a thickness of 6.7 cm. A total of 10,000 tonnes of asphalt concrete was needed to lay the wearing course.

Instruments: A viaduct scrutinised from every angle

Piers, deck, pylons and stays alike are equipped with a multitude of sensors. They are designed to detect the slightest movement of the viaduct and measure its wear resistance. Air speed indicators, accelerometers, inclinometers and temperature sensors are all part of the toolbox of measuring instruments used.

The data collected is transmitted via network to a computer located in the nearby operations centre at the toll gate.

The toll gate: a twisted leaf of concrete floating above the motorway

Near the viaduct's north abutment, the 53 concrete segments were poured using a single mould and transported on site by an articulated lorry, then taken over by a caterpillar crane to be placed in their permanent position.

Noteworthy features / Key figures

  • Emergency call points are spaced 511 m apart (compared to 2 km on normal motorway)
  • Two weather stations analyse atmospheric conditions over the viaduct and the toll gate (wind, humidity, temperature)
  • The concrete segments of the toll gate were manufactured in six months, from October 2003 to February 2004
  • The canopy weighs close to 2,500 tonnes