The 4940 m long Bogibeel bridge is currently the longest rail-road bridge in India. It is built on the mighty Brahmaputra river in Assam, 17 km away from Dibrugarh, and connects the city with the Dhemaji district. This two-tier bridge has a three-lane road on the top and a double line broad gauge railway track on the bottom.
The bridge design was proposed in 2002 and the construction began in the same year. It was completed in 2018 at an estimated cost of Rs 5920 crores.
The Bogibeel bridge has made life easier for the natives as well as the visitors of Assam and Arunachal Pradesh. It has helped in cutting down expenses and saving time by improving the connectivity of the area. The following list further elucidates the major connectivity advantages of the bridge:
- It reduces the vast distance of 444 km between Dibrugarh and Guwahati (largest city in Assam) by 55 km.
- The bridge links the Rangia-Murkongselek section of the North-East Frontier Railway on the north bank of the river and the Lumding-Dibrugarh section on the south bank.
- It connects NH-37 (Assam-Manipur) and NH-52 (Punjab-Karnataka), thereby improving connectivity with the southern states of the country.
- This bridge is also responsible for reducing traffic congestion in Guwahati.
- It also reduces the distance between Dibrugarh and Delhi.
- The bridge is a substantial asset as it aids in the speedy transportation of troops and essential supplies to the Tibetan borders in Arunachal Pradesh.
2. Construction Details
The bridge is an engineering marvel that has earned many technical firsts to its name. It is India’s first fully welded warren truss girder-type steel bridge and has used an incremental launching technique for the erection of superstructure.
2.1 Construction Companies Involved
The initial survey and geo-technical tests were carried out by Rail India Technical and Engineering Services, which is a government-owned consultancy firm. Further, Bhartia Infra Projects Ltd. (BIPL) constructed the bunds alongside the river as well as the embankments of the south bank.
Next, the foundation of the bridge was laid by Gammon India, one of the largest construction companies of the country. And last, the contract of building the steel superstructure was awarded to Hindustan Construction Company (HCC) in 2011.
2.2 Substructure Construction
The substructure of the bridge comprises of 42 double-D well foundations of size 16.2 m x 10.5 m. Each column consists of twin circular hollow piers of outer and inner diameters of 5.3 m and 3.3 m, respectively.
The depth of the foundation ranges from 42 m to 68.75 m. The abutment pier is composed of twin rectangular column of 4.6 m x 3.0 m and a height of 4.5 m. The pier caps throughout the bridge are 5.8 m wide, 15.9 m long, and 1.2 m thick.
The construction of the well foundations required a total of 30,00,000 bags of reinforced cement concrete (RCC) and plain cement concrete (PCC) of grades M35 and M25, respectively. It also required 2800 million tonnes (Mt) of structural steel and 19250 Mt of reinforcement steel.
The steel trusses were later launched on to these columns to form the entire span of the bridge.
2.3 Manufacturing of Steel Parts
Bogibeel is a fully welded steel bridge and the first of its kind in India. The country’s largest steel manufacturing company, Steel Authority of India Limited (SAIL) and Tata Steel, supplied rebars and other steel components for construction.
The steel members were first fabricated according to the requirement and then welded together in a workshop near the southern bank of the river.
Several modern techniques and equipment were used in this production process. The steel plates were moved using magnetic lifters to transfer them to different stations for fabrication. They were then chiseled into the desired dimensions by a computer numerical controlled (CNC) plasma cutting machine and oxy-fuel cutting machine.
In simpler words, a plasma cutting machine uses an accelerated jet of hot plasma to cut metals like steel, aluminum, and copper. This machine is run by a computer that controls the movement of the plasma jet.
Similarly, the oxy-fuel cutting uses a stream of oxygen instead of plasma to cut steel into the required shapes.
After the cutting process, the steel pieces were adjusted to the perfect thickness, and rough edges were smoothened. Following this, gas metal arc welding was used to join the steel members into a truss. To ensure long-lasting welds, the following tests were performed:
- Die penetration testing
- Ultrasonic testing
- Magnetic particle testing
Further, the exact surface roughness of the welded members was achieved using a blasting gun. Ensuring correct surface roughness helps in an even application of paint coating, which further aids in good corrosion resistance. Finally, the surfaces were coated with multiple layers of paint in a highly-controlled climatic chamber.
The fabricated steel members were then positioned correctly in the assembly workshop. First, they were joined by jacking and then welded by gas metal arc welding and submerged arc welding techniques.
The segments were arranged in a sequence and assembled vertically by horizontal lifters. After this, the top and bottom girders were also installed on the trusses, and the whole setup was examined thoroughly.
Lastly, a nose was fitted on the first truss before launching it on the pillars.
2.5 Establishment of the Bridge
For the launching of the bridge, hydraulic and strand jacks were linked to the substructure to enable the movement of trusses over the pillars. Two sets of steel wire ropes were anchored to the end cross-beams of the truss to facilitate this action.
The trusses were slid over the launching bearings with the help of sliding plates, which were inserted below the truss to be moved. As soon as one truss was launched, the next one was welded to it from one end, and the sliding plate was placed below it.
For making the process easier, ten spans of trusses were launched at a time. Each span weighed nearly 1700 metric tonnes. Subsequently, the launching bearings were removed and were replaced by spherical ones.
3. Protective Measures for the Structure
The structural endurance of the Bogibeel bridge has been increased manifold by incorporating the following measures.
3.1 Anti-Corrosive Measures
To minimize corrosion in different parts of the bridge, special-grade copper-bearing steel plates were used.
A thermal spray aluminum (TSA) coating was applied on the gusset plates and brackets. In this process, pure aluminum was sprayed on the surface to improve resistance to corrosion and heat.
The stringers and bracings of the bridge were galvanized with zinc. Also, a zinc spray was applied on the surfaces of the bridge, which were directly in contact with concrete.
Additionally, the exterior of the top cross girders and diagonals was given a coating of inorganic zinc silicate primer followed by epoxy, micaceous iron oxide (MIO) coating, and polyurethane.
MIO acts as an excellent barrier against moisture and other factors that accelerate the process of rusting.
3.2 Spherical Bearings
Spherical bearings were considered in the Bogibeel project due to their adjustable size and capacity to allow transverse motions and rotations. The bearings are made of steel with a polytetrafluoroethylene (PTFE) surface to enable smooth movement.
One side of the bearing is a spherical surface to allow slight turning while the other side is a flat surface to enable displacement. This increases the flexibility of the bridge.
A total of 164 bearings have been used with four bearings supporting each span. These were manufactured in Germany by Maurer AG, a steel construction company in Munich.
3.3 Seismic Measures
Considering that Bogibeel lies in the seismic zone-V, each bridge span has been equipped with seismic restrainers. These restrainers are used to prevent bridge superstructures from unseating during earthquakes.
3.4 Flood Measures
The Brahmaputra river has a history of recurrent floods, and to overcome this issue, dykes have been constructed on both banks of the river. This ensures that the area near the riverbank remains unaffected by floods.
The raising and reinforcement of the dykes have been done up to 9 km in upstream and 7 km downstream on both the banks.
Bogibeel bridge is 4940 m long and the longest rail-road bridge in India.
It constitutes of 41 spans of welded steel trusses, out of which the two spans adjacent to the banks are 32.75 m long, and the rest are 125 m long each.
A total of seven bridges are built over the Brahmaputra till date. These are: Bangabandhu bridge, Bogibeel bridge, Dhola- Sadiya bridge, Kolia Bhomora Setu, Naranarayan Setu, New Saraighat Bridge, and Old Saraighat Bridge.
Yes, the Bogibeel bridge has been functional since 2018.
The advantages offered by a steel-welded bridge are as follows:
Steel structures, in general, are durable and easily recyclable, hence providing sustainability. Moreover, steel bridges can be readily repaired by cutting out the damaged part and welding a new section in its place.
Welding is also faster and much cheaper than a construction done entirely of RCC and bricks.
Hence, it helps bring down the overall cost of the project and saves time.