A diamond-shaped cathedral of concrete and finely tuned steel, the Manaus-Iranduba bridge (known in Brazil as the Ponte Rio Negro, or Black River Bridge) rises from the Amazon jungle to span one of the world’s largest rivers, the Rio Negro. A massively complex structure, the bridge measures 2.2 miles in total length and boasts a 1,312-foot-long cable-supported central section that allows the Amazon’s significant shipping traffic to pass unimpeded.
Officially inaugurated on Oct. 24, 2011, the Black River Bridge is one of the largest bridges over fresh water on the planet, second only to the crossing of the Orinoco in Venezuela at Ciudad Bolivar. Connecting the regional capital, Manaus, to the interior of the Amazon, the bridge is spurring economic growth by increasing the flow of commercial, domestic and tourist traffic in the northern region of Brazil. Building the bridge, however, required an innovative approach and precise survey work.
Brazil is the largest country in South America in land mass and the fifth largest on Earth with a population of 190 million. Rich in natural and human resources, the country is divided by a complicated system of rivers with the Amazon at its heart, separating its territory into five distinctive regions. Brazil serves as the trade center and cultural crossroads for the entire South American region, but travel by anything other than air is difficult, if not impossible, because of the country’s rivers.
In 2007, Omar Aziz, the governor of the Amazonas, decided to span the Rio Negro, thereby increasing traffic and productivity between the two sites as well as the rest of northern Brazil and South America. As René Levy Aguiar, the secretary of the metropolitan region of Manaus explained, “To the north, the bridge will facilitate the connection to the state of Roraima and the Caribbean countries. To the south, it will allow a connection with highway BR-319 and the rest of the country.”
Making that connection would be costly. Construction of the bridge was originally projected at $570 million reais (approximately US$359 million). The government decided to maximize competition by breaking down the bids into stages of construction. Every stage of the project was separately contracted by the government, including primary surveying, pillar construction and insertion, spanning of the pillars with roadway, marine engineering, lighting and nautical signaling. The work was led by the Rio Negro Consortium, formed by Camargo Corrêa and Construbase. The benefit of the contracting plan was that government funds would be spread more broadly through smaller companies, none of which could take on the entire project alone. The downside, however, was that exact costs could not be predicted over the multi-year project in a region where little massive construction had been attempted before.
The Amazon region is well known for its extremes in weather. In Manaus, the tropical monsoon climate brings torrential rains, which create massive floods that inundate the surrounding areas.
The weather was only one of the challenges faced by the Rio Negro bridge crew as they attempted to span a portion of the river that experts knew very little about. The river’s variable depths, strong currents and diverse riverbed composition required engineers to be innovative in their approach. For example, the riverbed--a combination of rock, sand and clay--had to be excavated to depths of nearly 200 feet to secure the foundation piles. The firm designed floating construction platforms composed of 400 barges that were capable of supporting the heavy excavation machinery. These platforms were also used to carry the 30-ton pre-assembled steel frame structures used in building the bridge. A crane capable of holding up to 300 tons was used to position the piles.
Numerous delays plagued construction. Hurricane-force wind gusts of 75 mph whipped the massive cables about, and a severe lightning strike on the bridge damaged electronic equipment as well as hydraulics. Also, the extreme floods of 2009 pushed the banks of the Rio Negro out several kilometers into the surrounding landscape. A cable malfunction on the central span caused a 35-day delay. The smaller replacement parts were flown in by air, but the heavier pieces had to be shipped upriver by boat, which slowed the process considerably.
As Henrique Domingues, manager of the Rio Negro Consortium, describes it, “We had big challenges. First, the Rio Negro is a big river, so we chose the narrowest point where we could reasonably cross. Second, little was known about the geology of the region, so we had to do surveys for the foundations. The foundations required large-scale metal skirts that we had to drive into the riverbed with incredible force. Also, we knew little about the currents below the surface of the river. All this made the work a daily challenge and required new technologies and techniques.”
The survey work presented its own challenges; in particular, moving water does not make good reference points. “In the construction of a bridge, we have only two fixed points: the river banks, essentially to the north and south,” says surveyor Rosivaldo Marques.
After assessing the requirements of the contract, the Camargo Corrêa surveying team contacted local equipment dealer Santiago & Cintra to supply them with high-accuracy long-range total stations and optical levels that would allow them to provide the necessary measurements. Working from both the stable framing of the bridge and the constantly moving barges, the surveying crews had to adjust to a constantly changing environment due to wind surge, torrential rains and flooding. The right equipment was essential. “Without these total stations, this [work] would not have been possible,” Marques says.
The final cost of the bridge totaled $1 billon reais (US$569 million). More than 3,300 workers were directly involved with the bridge construction, and an additional 8,000 workers were tangentially involved with the project.
Today, the long lines of people waiting to cross the Rio Negro by ferry are a thing of the past. Traveling between Manaus and Iranduba now takes less than 10 minutes. An estimated 15,000 vehicles drive across the bridge each month, and that number continues to grow. By 2060, the traffic volume could reach up to 30,000 vehicles per week--a capacity that the bridge is designed to handle.
By easing the passage between two urban centers and facilitating access to northern Brazil and South America, the Manaus-Iranduba bridge is spurring economic growth in this Amazon region.
Project At A Glance
Location: Manaus, Amazonas State Capitol, Brazil
Client: Amazonas State Government, Manaus, Brazil
Contractor: Construtora Camargo Corrêa, São Paulo, Brazil
Topcon Dealer: Santiago & Cintra, São Paulo, Brazil
Primary Surveying Equipment
9 Topcon GPT-3107W Total Stations
2 Topcon CTS-3005 Total Stations
5 Topcon AT-G6 Optical Levels
4 Topcon AT-G2 Optical Levels
Length: 3,595 m (11,795 feet or 2.2 miles)
Road Spans: 73
Cable-stayed section: 400 m (1312 feet)
Center Span Height: 55 m (180 feet)
Central Mast Height: 103 m (338 feet)
Excavated piles: 246
Concrete Used: 138.000 cubic meters (452,800 cubic feet)
Steel Used: 14,500 tons