Engineers of NF Railway created a record of sorts when they carried out the rectification of the bearing arrangements of iconic Saraighat Bridge in Guwahati, Assam during a three hour traffic block on 12th January, 2018. Bearing 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.
It was probably during the 6.1 Richter scale earthquake of 21st September, 2009 that the bearings under two end girders got tilted. While this was not considered unsafe, the bearings in fact needed proper rectifications. The bridge was kept under observation and speed of trains was kept at 45 kmph.
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 Railway Engineers of Northeast Frontier Railway accepted this challenge. After thorough research and design, the Engineers decided that the tilted bearings of this bridge would be rectified.
Accordingly, 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. Requisite bearing members were arranged and heavy duty lifting jacks of 500 tonne capacity apart from other machinery were mobilised. To rectify the bearings without any hazard, the rail and road traffic on the bridge was suspended temporarily for three hours.
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. The bearings were removed from their place and installed back to correct inclination after cleaning etc.
After ensuring correct position of the bearings, the bridge girders were lowered back to original position. Road surface was brought back to original level. Rail track was also re-fixed and regular rail and road traffic movement was permitted within three hours.
It is to be mentioned that as a matter of abundant precaution, in addition to the active hydraulic jacks, two additional hydraulic jacks of 500 Tonne capacity and two mechanical jacks of 100 Tonne capacity were kept ready as back up arrangement.
To prepare for the worst scenario of an earthquake occurring during the work execution i.e. when the bridge would be in lifted condition, the girders were tied with cables with fixed structures.
The speed restriction of 45 kmph is planned to be relaxed now which would have far reaching implication on smoothening railway connectivity to Northeast India.