By David Bruce
Transportation is still basic in the Mekong Delta in Vietnam, where single-lane roads take carriage of rickety trucks, animal-drawn vehicles, bicycles and pedestrians.
On the mudflats of the Delta, 200 kilometres south-west of Ho Chi Minh City, construction has begun on the My Thuan Bridge. With its dual carriageway and pedestrian lanes, twin support towers and cable suspension, the My Thuan Bridge will replace the overladen car ferries that have carved out a business further upstream for as long as anyone can remember.
The Mekong River is a mighty, fast-flowing torrent of water that falls from the Tibetan highlands and cuts and turns for 4200 kilometres through China, Laos, Thailand, Cambodia and finally, Vietnam, where it fans out in a delta before emptying into the Vietnam Eastern Sea.
The My Thuan Bridge will span the Mekong River where it is 800 metres wide on unstable, shifting delta floodplain. For the agricultural communities of the region, the bridge will transform the daily task of moving produce, livestock and other goods. Construction of the bridge is now in its early stages and should be completed by the year 2000.
Australia has taken the lead role in the project. The $90 million project is two-thirds funded by AusAID and one-third by the Vietnamese government. Monash University is involved through its Faculty of Engineering, providing training in project management, design and construction along with construction company Maunsell, and with wind tunnel testing and river flow studies.
Monash and Maunsell have completed part of the formal training of the leading Vietnamese engineers charged with overseeing the project. Normally, training of this type would be done on-site in Vietnam, but for the My Thuan Bridge project, 35 Vietnamese engineers were brought to Australia for an intensive program in project management and specialised building methods.
According to Dr Le Nguyen Binh, a reader from the Department of Electrical and Computer Systems Engineering, who reg-ularly visits the My Thuan site, the project is extremely significant for Australia in developing links with Vietnam. "The My Thuan Bridge is the only AusAID-sponsored project of this scale in Vietnam, and Monash has been fortunate to be asked to contribute its expertise in managing such a project", he said.
The greatest challenge for the project team has been the instability of the riverbed. River studies were carried out in Monash's hydraulics laboratory under the direction of Associate Professor Bob Keller. Although the site is 80 kilometres from the coast, it is subject to tidal changes, typhoons and occasional major floods that would disrupt the fine sediments around the bridge pylons.
The
point is emphasised by Professor Paul Grundy, head of Monash's Department of
Civil Engineering: "It is a particularly delicate project because of the stability
of the riverbed. For example, if a new channel breaks through 20 kilometres
upstream during a flood, the water course at the bridge site could be altered
dramatically. What is a small crossing one day may be a major crossing the next."
A mere kilometre upstream, at the site of the existing river crossing, significant signs of erosion are already clear. So to stabilise the bank upstream, groins have been designed to prevent the river from further changing its course.
Another concern is the aerodynamic instab-ilities that might occur in high winds. Under extreme typhoon conditions, a bridge deck can flutter like a leaf. This phenomenon was investigated at Monash by Dr John Holmes and Professor Bill Melbourne, through wind tunnel tests in which a section of the deck of the bridge was constructed at a scale of 1/125 and mounted on a spring support system to simulate the motions of the deck. The studies found that the My Thuan Bridge design was stable up to wind speeds of 85 metres per second - well above the design wind speed for Vietnam.
The
Monash connection is continuing, with Dr Binh and Mr Quy Le, from the Department
of Civil Engineering, regularly visiting Vietnam to view the early stages of
the construction.
Monash's Mr Quy Le visits Vietnam regularly to monitor construction.
For information on the wind tunnel and other engineering expertise available through Monash University, call the Engineering faculty on (03) 9905 3404.