By Richard High25 April 2008
Large structures form the heart of any country's infrastructure, and economic prosperity depends on a network that allows the movement of manufactured goods, and materials and people quickly and cheaply. Richard High reports on some of the latest projects.
Addressing the board of governors of the World Bank in Singapore in June this year, World Bank president Paul Wolfowitz said, “Across Africa, crumbling infrastructure has held back business expansion and opportunities in international markets.
“Today, an entrepreneur in Central Africa pays more than three times what his Chinese counterpart pays to transport a container the same distance. For that African entrepreneur, the path out of poverty is literally a paved road.”
Building new infrastructure links, such as ports, bridges, canals, railways and airports, said Mr Wolfowitz, not only boosts competitiveness and economic growth in developing markets like Africa and Latin America, but also alleviates poverty and spreads wealth. Put simply, a country’s infrastructure is its life-blood.
A case in point is the new Tangier Mediterranean Port in Morocco. Currently taking shape about 35 km east of Tangier, it will be Africa’s largest port when completed in 2007. The crossing point of the north Atlantic and Mediterranean trade routes it will be capable of handling the world’s largest ships, and be a vital transhipment hub for over 25 million tonnes of goods into and out of the continent.
It is part of a larger, MAD 8.7 billion (US$ 990 million), regional infrastructure initiative that includes railways and roads that will link to the port. These links are designed to allow Morocco’s manufacturing base, which is mainly based in the north of the country, and the region’s farmers, access to international markets for their products.
Construction is being carried out by a joint venture of Italy-based Saipem and French contractor Bouygues under a MAD 2.42 billion (US$ 280 million) design and build contract. The works, for the Special Tangier Mediterranean Agency, part of the Moroccan Government, are expected to take 36 months.
This includes two breakwaters, one of which involves placing 40 precast concrete caissons in water up to 20 m deep, and redging 4.58 million m3 of sand and gravel followed by installation of 660000 m3 of rip-rap (irregular shaped stones placed randomly to protect against erosion and scour).
The breakwater starts as a conventional structure, protected by 7500 Accropodes (interlocking blocks concrete blocks purpose-designed for the protection of coastal areas), which form a partially submerged bund. As the structure encounters deeper water the caissons replace the Acropodes. The caissons’ shear face, rather than the Accropodes’ sloping design created an extra 18 ha of operating water within the port because ships are able to manoeuvre closer to their walls.
Designed by UK-based Halcrow, the space saving breakwater led to Bougyues landing a further MAD 243 million (US$ 27.6 million) contract to design and construct a new oil tanker berth and goods quay.
The height of a 10 storey building when finished, the caissons are partially constructed on land. Cast at a rate of one per week, the first 9 m, weighing 3200 tonnes, is transferred to the water for completion. Once secured in a dry dock 15 m is added to its height, bringing the total weight up to 6000 tonnes.
Once complete it is towed to the site and, with the aid of GPS, sunk into position. This is done during low tide, thereby avoiding the Straits of Gibraltar’s fierce currents.
Over 13500 m3 of sand is then used as ballast. An extra 6 m of cast in-situ concrete is then added to bring the final height of the breakwater to 35 m.
Regional trade hub
Also gearing up to be a regional transhipment hub is the port of Salalah, Oman. Lying just 150 km north of the region’s main East-West shipping lanes, it has established itself as one of the world’s top 20 ports, thanks to its deepwater draught.
Its present expansion includes the construction of two new berths, at a cost of OMR 101 million (US$ 262 million). Middle Eastern Consolidated Contractors Company (CCC) and Cypriot contractor Hani Archirodon started work in August 2005. Although the whole scheme is due for completion in August 2008, Berth 5 has to be delivered by November this year.
The new berths will extend the 345 m wide quay out into the ocean by 1 km and double the port’s capacity. The seabed will be deepened from its current 16 m to 18.5 m in order to accommodate the new S-Class container ships’ draught.
Like part of the breakwater in Tangier, the face of the quay wall is to be made up of interlocking concrete 25 tonne Accropodes. However, here it will be supported by geotextiles, backfilled and capped with concrete.
Besides the 345000 m2 quay, a 2.8 km long, 25 m high breakwater is needed to protect ships against the 12 m high waves common during the monsoon season - June to August. In total, 6.5 million tonnes, or 10 million m3 of rock will be needed.
Its supply is the responsibility of land works manager, Costandi Khoury. Using 250 tonnes of explosives/month, almost 13000 m3of rock is produced every day from the area’s numerous limestone quarries. Besides the rough hewn rock required for backfilling, an enormous amount of crushed rock is also required for the 500 m3of sulphate resisting concrete the project needs daily.
With 500 pieces of equipment on site, over 300 are dedicated to the land operations. These include eight 46 tonne, Volvo EC460B excavators, three Volvo L220E wheeled loaders and 20 Volvo haulers. The eight excavators are loading 300 m3 an hour, although this varies by the number of trucks available - normally nine, the size of material being specified and the cycle times.
Bridging the gap
Moving goods and people across water by ship is one solution; another is to construct a bridge. To date, crossing the Changjiang River, in China’s Jiangsu Province has only been possible by ferry. All that is set to change with the completion of the Sutong Bridge in 2008, which will be the first cable-stayed bridge in the world to break the magic 1000 m span barrier.
The six-lane, 1088 m span bridge, which will cut journey times by 55 minutes, also sets a new benchmark with its two, 306 m high A-shaped pylons. According to Doka Shanghai sales manager Roger Zhang, construction of the pylons has presented an immense challenge to main contractor China Harbour Engineering Group (CHEC) and formwork manufacturer Doka.
Mr Zhang told iC, CHEC had previously used Doka’s climbing-formwork systems on the 210 m high, Run-Yang Bridge pylons, and the 162 m high, Yang-Luo Bridge pylons. “What impressed CHEC then was the speed, high level of safety and immaculate surface quality our climbing systems provide” said Mr Zhang.
At present the pylon’s A-shaped legs are rising by two 4.50 m high sections every week. Key to this has been 36 of Doka’s SKE 100 automatic climbers. When complete the SKE 100s will have cast 68 sections each.
Crane-independent SKE 100s are also at work on the bridge piers. Anchored to the structure at all times, their working platforms enclosed on all sides, they offer a high level of safety, said Mr Zhang.
“The SKE 100s are moved using powerful hydraulic jacks, even in wind speeds as high as 70 km per hour. Typhoons are not uncommon in the region either,” said Mr Zhang. “Construction is also using the world’s tallest tower crane, a specially modified Potain MD 3600 with a height under hook of 306.4 m, and some of the most powerful concrete pumps ever, which are supplied from a concrete plant constructed on one of the pylon islands.”
As the Changjiang River is a busy waterway the long bridge will have a shipping clearance profile of at least 891 by 62 m. The 8146 m long bridge will be part of the national motorway network linking Shanghai and Suzhou.
In the US, the four-lane Otay River Bridge, California, US is a more conventional structure. Part of the US$ 775 million South Bay Expressway, the bridge is a design-build contract carried out by the Idaho Washington Group International and Flour Daniel joint venture.
A precast segmental balanced cantilever structure it consists of twin box girders with a total length of 1012 m. Typical spans are 90.5 m and consist of 28 precast segments. The pier tables and columns are cast in-situ concrete with columns reaching up to 50 m.
The foundations consist of 110, 1.83 m diameter CIDH (cast in drilled hole) piles, 10 each per footing, and 14, 1.22 m diameter CIDH piles, seven per abutment. The substructure consists of two abutments and 11 piers.
To lift the 1.8 to 2.7 tonne rebar cages, lifting contractor Marco Crane & Rigging used two 272 tonne Link Belt 348 lattice boom crawler cranes. The cranes were also used to lift the 35 tonne 21.3 by 4.9 m, concrete bridge deck segments.
Elsewhere, the joint venture used a hydraulic jacking system to lift over 644 precast pier segments. Weighing in at 72 tonnes, including approximately 3 tonnes of reinforcing steel, the segments are about 5 m high.
According to a joint venture spokesman, this segmental construction method allowed the top of the bridge to be put together from above, making it a more environmentally friendly way to build, as it minimizes impact on the sensitive valley floor below.
Water concerns of a different kind have seen construction of a new, 60 km long canal in California’s Coachella Valley, US. Designed to preserve the region’s water supply, vital to the area’s desert farmers, the original 198 km long earth lined canal has gradually been replaced by a concrete lined one to prevent seepage.
In October 2004 main contractor R&L Brosamer broke ground on the US$ 71.2 million, 2.5 year long project. When complete in April 2007 it will preserve over 32 million m3 of water that was being lost annually to seepage.
In addition to construction of a new, parallel concrete-lined canal, 26 double box culvert structures and six check stations - for water level control - were also built. About 61 km of fencing was also required to keep the endangered desert tortoise and other wildlife out of the canal. Large watering ponds were also constructed, as the canal will not be accessible to animals once construction is completed.
The canal work entailed excavation, embankment placement, trimming and lining, and the construction of several double box siphons with accompanying inlet and outlet transitions. This meant excavating 4.28 million m3 of earth and compacting 356000 m3of embankment.
After canal excavation came canal trimming and lining. The canal is 18.3 m wide at the top, 4.9 m wide at the bottom and 4.8 m deep with sloping sides. A Brosamer-owned full prism trimmer was custom built and adjusted on site to fit the canal shape.
The canal trimmer moved through the excavated area to trim the ground to the correct grade and shape the canal in preparation for the concrete lining. This left 1.1 million m2 of trimmed dirt. Then, the full prism canal paver paved the canal in one pass with concrete, at a 75 mm thickness, sides and bottom, which required 84000 m3 of concrete.
There is no doubt that large structures - ports, bridges, canals, railways, roads and airports - will continue to play a vital part in the future development of many regions. Latin America, Asia and Africa will only continue to prosper economically if they can get their goods to market efficiently.
The regional development banks will also continue to play a large part in making these schemes happen. Governments alone cannot deliver.
The private sector, through public private partnerships, will also have a role to play. Only when all three work together can true progress be made.