Riverbed scouring makes several piers vulnerable; overloaded trucks damage deck, expansion joints; experts suggest immediate repairs
The Meghna Bridge is under threat as riverbed scouring has left several piers vulnerable while high traffic volume and overloaded trucks are damaging the deck.
Experts who surveyed the bridge called for immediate repairs. The Meghna Bridge is crucial to smooth road communication between Dhaka and Chittagong.
There has been extensive damage to expansion joints and hinge bearings of the bridge. The Roads and Highways Department engineers blame it on very high volume of traffic on the two-lane bridge and unforeseen erosion of the riverbed near the pier foundations.
The authorities concerned say that they would soon enforce a speed limit on the bridge and put signs warning vehicles about the damaged bridge. They fear the situation would worsen if repairs are not done immediately.
The bridge was opened to public in 1991 when the authorities estimated that around 5,000 vehicles would use it every day. Now the traffic is four times that figure.
The bridge is now very bumpy and there is always a banging noise every time vehicles cross the expansion joints, all making for a very scary ride.
All the 13 expansion joints have been badly damaged. Most of the nuts and bolts of the joints are missing and it is vibrating alarmingly when heavy vehicles go over them.
The bridge has 12 pier foundations on which it stands.
RHD engineers believe that the scouring of the riverbed could have been the result of large vessels plying underneath. However, former vice-chancellor of Bangladesh University of Engineering and Technology Prof AMM Shafiullah said, “Fast water flow has caused the scouring. The RHD should have monitored the bridge and resolved all the problems.”
The authorities had apprehended deterioration of the structure over the years by observing scouring of the riverbed. Last year, the RHD appointed a Malaysian-British consulting firm to examine the bridge and prepare a design for its rehabilitation. Based on underwater inspection findings and data analysis of detailed hydrological study, experts concluded that five piers (pier 6-10) of Meghna Bridge are under threat due to scouring and disintegration of concrete.
As a result, piles are not having the support it should and they are more susceptible to earthquake damage, the firm mentioned in a report submitted in February this year.
It found 15 metres of scouring at pier-8, which is considered very risky. “Any damage to it would affect other foundations too, endangering the entire bridge,” a RHD engineer told The Daily Star.
Sources in the RHD said an incorrect estimate of future traffic volume by the Japanese designer put the bridge in such a state within just 20 years. The designer had not thought about so overloaded vehicles either. It had estimated movement of 500-tonne vessels under the bridge but now ships weighing between 3,000 and 5,000 tonnes ply the river under.
“Scouring happens where ships ply,” said a RHD engineer, adding that the other pier foundations have no problem with scouring as no large ship cross the bridge near them. Sand lifting from Meghna Bridge is another reason of scouring, he added.
The RHD tried to fix expansion joints in 2008 but that did not last long. The repairs were undone due to plying of heavy vehicles.
Most of the 36 hinge bearings have also been affected. Eight bearings are in such a poor condition they require replacement while the rest should be repaired, suggested the experts.
Since there is no alternative to the bridge on Dhaka-Chittagong highway, any disruption will have enormous impact on business and economic activities. Also known as the First Japan-Bangladesh Friendship Bridge, the 930 metre Meghna Bridge was built with Japanese grants by Koei Co Ltd.
BID CHALLENGE
The government will face a stiff challenge restoring the bridge, which should hopefully start early next year. Since the bridge is a single carriage way, the authorities have to stop vehicular movement for at least several days to do the massive work.
The government has already taken a Tk 150 crore restoration project for the bridge. “We are expecting that the project will be approved soon so that we can float an international tender,” said Shahabuddin Khan, a superintendent engineer of RHD, who is looking into the Meghna Bridge problem.
He said the government is doing everything quickly as any delay in restoration might compromise the bridge’s 100-year lifespan.
Shahabuddin said concrete blocks will be dumped around the affected pier foundations so that sedimentation takes place to fill the scouring as per recommendations of the investigation firm.
MEGHNA-GUMTI BRIDGE
The consulting firm also suggested repairing the 1,410-metres Meghna-Gumti Bridge (also built by the Japanese and opened to public in 1995) as many of its hinge bearings and expansion joints were damaged.
Meghna-Gumti Bridge is only a few kilomtres away from Meghna Bridge but its condition is not as bad as Meghna Bridge’s.
-With The Daily Star input
