Spanning Southern France
A construction project that results in quicker commutes for its residents and cleaner air is easy to admire but not unheard of. One that will rise to a height greater than that of the Eiffel Tower, however, is rare. In fact, the Viaduc de Millau in southeast France is the only landmark development in Europe that will be able to claim all three achievements upon its scheduled completion in January 2005.
Thanks to the bridge project for the A75 highway section from Clermont-Ferrant to Beziers, motorists from French cities and northern Europe will reach their destinations on the southern coast of France and the Spanish Mediterranean coast up to four hours faster than before. Travel will be easier for those on their journey to the popular region between southern Montpellier and Clermont-Ferrand, an area famous for its old castles of the Templer Knights and the Kartharer, an early religious protestant group of the 13th century that separated from the Vatican and tried to reform clerical life. The river valley and nearby gorges and ravines of the Tarn River Valley in southwest France, which comprise a historic cultural and unique recreational landscape well known for its water sports, is now being enhanced by one of the most impressive civil engineering feats of our time. Even during the construction phase, the Viaduc de Millau has turned into an attraction for southern France’s residents and commuters as well as visitors and tourists. Millau’s 20,000 residents can also breathe easier—literally—since the bridge opening will put an end to decades of environmental damage caused by the endless lines of vehicles and traffic jams. The 2.5 km highway bridge, boasting two-lane decks that span the Tarn River in both directions, is a technical masterpiece of the highest order and a hallmark of state-of-the-art technology.
The Artists and Their PropsThe highway bridge being constructed over the Tarn River will be higher than the 312.27 m high Eiffel Tower constructed for the World’s Fair in Paris in 1889 by Gustave Eiffel. Even the last recording of its height in 2000 at 324.00 m will be beat by the Viaduc de Millau. The highest of seven bridge piers will reach a height of 255 m and the engineers will affix an 87 m high steel pylon on top, allowing for a total height of 343 m.
The bridge and the towers bear the aesthetic hallmark of bridge construction engineer Michel Virlogueux and the famous architect Lord Norman Foster, an award-winning designer of the new Hong Kong Airport Chek-Lap-Kok and its bridges, the German Parliament Building at Berlin, the London Millennium Bridge, and many other world-reknowned projects. Civil engineering specialists Eiffage TP and affiliate company Eiffel, the largest metal construction group in France and the fifth largest construction group in Europe are also part of the construction group. The surveying is directed by Surveying Engineer Diplome Grandes Ecoles, Pierre Nottin of Service Topographique Eiffage TP. The construction measurements and controls for the Viaduc de Millau are being carried out using surveying systems from Leica Geosystems (Atlanta, Ga.).
Establishing the CanvasThe completed Millau bridge will not only be the highest bridge in the world, but its seven piers also make the 2,460 m long Viaduc de Millau the world’s longest cable-stayed bridge with several central suspension pylons. Each of the seven bridge piers has its own major construction site, together with two 12-person teams working two shifts. Added to that are the two construction sites on either side of the sloped valley for the lateral ramps, with welding teams for the deck’s steel sections. Two production mills were built in the middle of the valley, one for steel fittings and one for concrete, as well as office trailers for the site management and surveying teams. The elements for the steel roadway profile plates are being produced in the Eiffel Lauterbourg plant in eastern France, assembled in the Fos plant in southern France, transported to Millau in special heavy trucks and welded together directly at the two ramp construction sites. The first of a total of 16 steel roadway sections, 171 m in length, 32.05 m wide and 4.20 m high in the form of a trapezoid profile, have already been welded and maneuvered with 1,000-ton hydraulic jacks from the southern ramp toward a scaffold frame construction between the ramp and the first suspension pier on the southern side of the valley. As it was being negotiated into place, a Leica 530 GPS system continually recorded and monitored with millimeter precision where the imposing deck section was located above the valley, in terms of the plan, scaffold frame construction and pier.
Compared to the Eiffel Tower with its 7,500-ton steel structure, the record-breaking Millau engineering project will need 36,000 tons of steel and 206,000 tons of concrete. With a distance of 342 m between the piers, their eastward alignment forms a slight curve and causes a continuous north-south downward deck gradient of three percent. The uppermost 90 m of the concrete piers are divided in two, with the appearance of a tuning fork. That means that the lowest pier, which is 78 m in height and built directly into the northern slope edge, was encased straight from the base in this basic split-filigree form.
The highest pier (P2) begins at the foot of a foundation that is 16 m deep, has an area of 200 m2 and is anchored in concrete. It tapers increasingly toward the top to a height of 165 m where it forks upwards for a further 90 m. At the upper end, the pier’s bearing area still has a cross section of 30 m2. The precast steel roadway profile plates will be connected to this uniquely designed bearing area using a special system. Fastened at the tops of the pier’s 87 m high steel pylons are 22 steel stay cables. These lead to the strong center support of the steel roadway profile plates and transfer the force from the piers to the foundations and the construction as a whole. A total of 14 171 m-long and two 204 m-long trapezoidal steel roadway profile plates, each 32.05 m wide and 4.20 m high, are being joined together on the lateral ramps, maneuvered towards the middle of the bridge by hydraulic presses, connected to the piers and anchored to the seven steel pylons with a total of 154 steel stay cables. The 32.05 m-wide roadway profile plates offer enough room for two, two-lane decks of opposing traffic with emergency shoulders, a reinforced, load-supporting center section and 3 m-high protective sidewall wind barriers.
Coordinating the CoordinatesAs the first expert on the scene in August 2001, Pierre Nottin established the front line of more than 400 specialists, including a five-member surveying team, to work on the construction site. According to the instructions and drawings of the civil engineers and the architect, Nottin established a local observation grid to determine coordinates in the Global Positioning System as well as for simultaneous contact-free measurements using conventional surveying instruments. A Leica GPS 530 RTK reference station was installed in a surveying pier anchored in the natural rock of the mountain slope and integrated into the local government coordinate network via transformation into WGS84. Using mobile Leica GPS 530 systems, the coordinates of the pier foundations were then determined and all subsequent steps in the construction experts’ work process tracked and calibrated. The main task of the five surveying specialists during the initial two years was to determine the formwork positions with various cross sections of the entire 4 m of the slipform’s height. The raising and fitting of the formworks must be determined with the utmost precision and continuously monitored at a total of 256 levels.
According to the individual form of the pier cross sections, which taper upwards and diverge from each other once they have reached a certain height, the self-climbing slipform has to be continuously adapted to the horizontal angles and gradients each time another 4 m of pier concrete are poured, as well as having to be precisely positioned to within just a few millimeters. It takes three working days to concrete a 4 m-high slipform feed, meaning that a pier can “grow” as much as 8 m each week. After pouring more than 200,000 tons of concrete, nearly all of this work is completed.
To monitor the construction project, 12 conjointly secured fixed reference point piers were installed along the bridge axis at well-accessible points, allowing survey measurements using forced-centering Leica tacheometers and reflector prisms as well as GPS antennae. So far during construction, 200 of a total 300 survey reflector prisms have been cast into the outer encasement of the concrete piers and fixed in natural rock. Additional precision reflectors will be fixed on other important structural elements of the bridge. These durable and eternal gold-coated “diamonds” will help register even the slightest of changes in this masterful structure with a high level of precision from the fixed reference points. The slightest of changes in the bridge piers, such as those due to temperature fluctuations and stresses, can be automatically targeted and monitored, benefiting not only the construction surveying team but also the geometrician. Nottin’s surveying team relies on the precision tacheometers Leica TCA 2003 and Leica TC 1103 in addition to its Leica GPS 500 system. The geometrician uses a Leica TDA 5005 industrial tacheometer to determine his coordinates in conducting control surveys, ensuring accuracy to within 0.3 mm. Numerous leveling instruments and digital levelers are also being used.
Nottin believes he has everything securely under control. “What I’ve learned from many years of engineering surveying with conventional instruments is proving to be the case here, too,” he says. “The precision and reliability of the GPS and TPS systems are helping us to fulfill complex surveying tasks at the highest possible level on the Viaduc de Millau.”
A Work of Art With a 120-Year GuaranteeThe Eiffage Group guarantees the bridge’s functionality for 120 years. By then, there will be different GPS satellite systems circling the globe than the ones with which it was calibrated. The massive yet aesthetically pleasing bridge will open in January 2005. The Viaduc de Millau will shorten the path between Clermont-Ferrant and Montpellier/Beziers by 100 km and will eliminate the current traffic problems on the A75 highway section, which in the peak travel season can have waiting times of up to four hours on a 50 km stretch.
And with its impressive stature, perhaps the Viaduc de Millau will become the most well-known monument in Europe, breaking yet another of the Eiffel Tower’s records. If not, at least numerous commuters and visitors will be able to travel—and breathe—with ease.