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Kolia Bhomora Setu
Kolia Bhomora Setu is a concrete pre-stressed concrete bridge in the city of Tezpur in the north eastern state of Assam and is one of the finest examples of engineering marvel in the country. The bridge owes its name to General Kolia Bhomora Phukan of the Ahom dynasty which ruled over the region of Assam for 6 centuries. Created over the river Brahmaputra, the bridge connects the district of Sonitpur to Nagain. The bridge spans over 3015 meters and took 6 years of construction. The bridge has hugely contributed in the development of India’s north east. Brahmaputra River (on which the bridge is made) not only cuts through Assam but also bisects the north eastern states with India’s mainland.
Brahmaputra is one of the largest rivers and is even troublesome for engineers due to its vast size and unpredictable nature. The river also causes a major reason of connective deficiency with these seven states despite the efforts by Indian Railways.
Geography
The Kolia Bhomoru Setu is located in the town of Tezpur. Tezpur is one of the largest towns in Assam and is known for its considerably large population. The town lies on the banks of Brahmaputra. Considering the fact that the town of Tezpur is located on the foothills of huge mountains, it gets very fast flowing rivers which includes the Brahmaputra that has strong currents in this district. A large number of hillocks around the town protect the district from flood. The winters are usually mild in Tezpur but the summers usually become harsh and humid.
Description of the Bridge
The Kolia Bhomoru Project was a special project for the government of India as it strengthens upon reaching the seven sister states by connecting them to the main land. The project started in 1981 and was finished and commissioned into public uses in 1987 post which people used its 3kms long road to cross the Brahmaputra with ease.
Foundation
There are 27 foundations of the bridge out of which a total of 25 are open wells. Raft foundations are also used in the first pier and in the North abutment. The wells were dug as down as 56metres to tackle and negotiate any seismic disturbance. The encountered strata were hence mixed with pebble to make it stronger.
Wells
Caissons were launched in order to ease the formation of a couple of wells. Caissons were used in deep waters, depth of which ranged from 7 to 12 meters. Huge amounts of steel were fabricated for this purpose. The construction material had to be ferried from the river bank to the location which used a fleet of country made boats and a total of 20 tugs.
Caisson Grounding
The second pier was designated to be sunk close to the Bhomoraguri hill. To enable that, strata of boulder was placed 26 meter below. Deep see divers were deployed for this task and a series of underwater blasts were done to ensure this.
The wells now have been surrounded by highest standards of construction that maintains its fidelity even during the seismic movements in the region and violent flow of the Brahmaputra’s current.
Super Structure
There is a distance between the two piers which is approximately 120 meters. The engineers have covered this distance by attaching cantilever with the consecutive Piers. Along with that a span of 15 meters was suspended from the very middle. The portion of the cantilever was made up with P.S.C, Box-girder which was used with a grade M-425 concrete. Special cement was used with it. The cement was later treated for post tension. These cantilevers are of varied lengths and have been created in 11 segments. In order to enhance the rigidity of the tension, Diaphragms were added to the cantilevers, especially to the ones in the 11th segment. Due to the vastly unpredictable nature of Brahmaputra and the small amount of time available for the construction, the pre construction became important before the actual laying down of these elements. They were created at a daily average of 7 meters per day which meets the common international standards of its constructions.
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