Bearings under two vital girders of the 56-year old Saraighat Bridge on the Brahmaputra here, which are believed to have got tilted during a major earthquake in September 2009, were finally repaired and put in place after a gap of more than eight years, with the Northeast Frontier Railway claiming it to be a record of sorts.
“Engineers of NF Railway created a record of sorts when they carried out rectification of the bearing arrangements of the iconic Saraighat Bridge during a three-hour traffic block on January 12. Bearings are the arrangement by which the bridge rests on the piers (pillars). They not only link the bridge girders to the pillars but also facilitate the lateral movement of the bridge as a result of expansion etc,” NF Railway CPRO Pranav Jyoti Sharma said here on Tuesday.
Though the railway authorities are not exactly sure how the bearings got tilted, the suspicion is that it was a major earthquake measuring 6.1 on the Richter scale that had occurred on September 21, 2009 that had caused the damage. “It was probably during the 6.1 Richter scale earthquake of September 21, 2009, that the bearings under two end girders got tilted. While this was not considered unsafe, the bearings in fact needed proper rectifications,” Sharma said.
While the bridge was kept under round-the-clock observation for more than eight years, the railways kept it a closely-guarded secret so that there was no panic at any time. Train speed was kept at a maximum of 45 kmph since then, with the railways looking for the right opportunity to set things right. “Rectification of the bearings was indeed a herculean task as the ends of the bridge girders were to be lifted by about 10 centimetres. Such work was never taken up earlier. The team of engineers of Northeast Frontier Railway however readily accepted this challenge, and after a thorough research and design that took several years, they decided that the tilted bearings of this bridge would be rectified,” CPRO Sharma said.
The 1.492-km rail-cum bridge in Guwahati that is aptly named Saraighat Bridge – after the historic Battle of Saraighat of 1671 in which the Assamese had defeated the Moghuls – is the first bridge on the Brahmaputra, and was hurriedly opened for military use during the Chinese aggression of November 1962 even before it was formally inaugurated.
CPRO Sharma said that while necessary preparations were made to deal with all kinds of possible adverse situations that could occur so as to avoid disruption to this vital connectivity, the engineers not only arranged requisite bearing members but also heavy duty 500-ton capacity lifting jacks and other machinery.
“While rail and road traffic on the bridge was suspended for two hours to conduct the operation smoothly, two separate teams of engineers and skilled workers were deployed on both sides for rectification of bearings. Hydraulic and mechanical jacks were installed under the railway girders. With the help of these jacks, the railway girders were lifted as required,” he said.
The engineers worked on a war-footing, first removing the bearings from their place and then installing them back to the correct inclination after cleaning. “After ensuring correct position of the bearings, the bridge girders were slowly lowered back to their original position. Simultaneously, as road surface was brought back to original level, the rail track was also re-fixed, all within three hours,” the CPRO said.
He also said that while two additional 500-ton hydraulic jacks and two 100-ton mechanical jacks were kept ready as a back-up measure, the engineers also kept in mind what to do in the event of an earthquake occurring during the three-hour operation. “To prepare for the worst scenario of an earthquake occurring during the work execution, that is when the bridge would be in lifted condition, the girders were tied with cables with fixed structures,” Sharma said.