Jamuna bridge and dual-gauging unite the BR network
Work to join the two halves of the Bangladesh Railway network across the Jamuna river will be completed this year
Engr Iqbaluddin Choudhury was formerly General Manager & Project Director, Jamuna Bridge. He has since been appointed Chairman of Rajuk, the Dhaka Development Authority, and has been succeeded by Engr AFM Mostafizur Rahman
BANGLADESH Railway has cause to celebrate this year. When the last section of rail on the 99 km new line from Jamtoil to Joydebpur is laid, it will complete a long-awaited link uniting the eastern and western parts of the national network. At the heart of the link is the Bangabahdhu bridge over the mighty Jamuna river, known in India as the Brahmaputra. The bridge and associated links on each side overcome one of the major historical impediments to the development of Bangladesh.
Not that it has been a simple matter. Historically, the country's rail network has always been divided. That era is now over, and it will not be long before trains can run through from the capital city of Dhaka to all parts of the western network.
When the original network was built, there were two distinct flows of traffic. One originated from the port of Kolkata with its hinterland of the northern parts of Bengal and Lower Assam. This was carried on what became the 1676mm-gauge main line of the Eastern Bengal Railway; metre-gauge feeder lines connected towns such as Bogra, Kaunia, Dinajpur and Mogalhat.
The second flow served the port of Chittagong, covering East Bengal, Assam and the rest of North Eastern India. This was the Assam Bengal Railway's network, which was entirely metre gauge. The limited amount of cross-river traffic between the two networks was handled by ferries.
With partition in 1947, traffic patterns changed. In the east, traffic flowed to and from Dhaka and the ports of Chittagong, Khulna and Mongla, stimulating the development of the metre-gauge network. Meanwhile, the broad gauge in the west became less important as traffic declined.
In the late 1980s the Bangladesh government finalised a project to build a multi-purpose bridge over the Jamuna. The river carries formidable flows of water with a huge sediment load. Its channels constantly change course with sandbanks appearing and disappearing every year. The width between firm banks varies from 10 km in the dry season to 40 km during the monsoon.
The original plan was for a four-lane road, power supply connection and a gas pipeline with provision for a metre-gauge track. Broad gauge was subsequently added to the plans. It was accommodated by strengthening or modifying the structures, although this was not ideal as the construction process had already begun. This meant that the full loading capacity of broad-gauge trains could not be exploited, and a compromise was agreed. This entailed the following restrictions:
- only a single six-axle locomotive with an axleload of no more than 18 tonnes is permitted on the bridge;
- an empty wagon must be marshalled behind the locomotive of all trains;
- the equivalent uniformly distributed trailing load may not exceed 43·7 kN/m; this is adequate for ISO loading, but short of the broad-gauge norm where 75 kN/m is permitted.
- resurfacing of the road portion of the bridge will be restricted to a depth of 50mm instead of the 75mm originally intended.
As finally constructed, the bridge is 4·8 km long and 18·5m wide. It is has post-tensioned, pre-cast, segmental and progressively-balanced cantilever box girders supported on 121 tubular steel piles. The 49 spans carry a pair of two-lane carriageways, a single dual-gauge track, a 750mm diameter gas pipeline, a 232 kV electricity transmission line and optic fibre cables. The dual-gauge track has been laid with a symmetrical four-rail configuration whereby the rails of both gauges act as guard rails.
The bridge was opened to road and rail traffic on June 23 1998. The first train ran from Jamtoil in the west over the bridge to a new station named Ibrahimabad, and regular broad-gauge services have been maintained ever since. Tracklaying on the dual-gauge Jamtoil - Joydebpur link is due to be completed this month.
Work is meanwhile in hand on converting 245 km of broad-gauge route in the western sector to dual-gauge. This will allow metre-gauge trains from the east to reach the western metre-gauge lines at Santahar and Parbatipur. Dual-gauge track will continue west from Jamtoil to Ishurdi, where a chord will bypass the town. From there dual gauge will run north all the way to Parbatipur.
A separate project will see the 35 km of metre gauge from Joydepur to Dhaka converted to dual gauge, giving broad-gauge services direct access to the capital for the first time. This work is expected to be finished by the end of 2003.
The entire programme entails construction of nearly 360 km of dual-gauge track. Apart from the four-rail section over the bridge, a three-rail configuration is used.
Funding for the dual-gauge work has come from an aid package administered by the Asian Development Bank. The cost of the bridge, the new line and the conversion work totals US$341m, of which the ADB has financed US$110m and OPEC US$15m. Local costs of US$185m are being met by the Bangladesh government. The rest of the funds are from France, Spain and suppliers' credits.
Canarail are the main consultants, in association with Systra of France and local firm Technoconsult International.
The project was split into two contracts. That for the section from Jamtoil to Joydebpur was awarded to a consortium of civil engineers Samwan of Korea and track specialists Travaux du Sud-Ouest of France. The civil works for the new line between the bridge and Joydebpur included 91 box culverts and 63 bridges with a total of 130 spans varying in length from 10m to 100m. Signalling and telecommunication works will be finished in November.
The second contract for converting 260 km of broad-gauge track to dual-gauge was awarded to Ircon International of India. It includes civil works for the Ishurdi bypass. This contract is due for completion in December this year.
Type BS 90A rail has been imported from China and India by the project management team, but all other materials are being procured by the contractors. CWR is being used throughout.
Originally the dual-gauge track was to be laid on wooden sleepers, but this was later modified to prestressed concrete sleepers. These are being procured from India.
With this design, no packing is needed under the metre-gauge rail and the load from this centre rail is supported on the broad gauge rail seats. This means that only broad gauge tampers will be required. Each sleeper weighs 365 kg, making them among the heaviest in the world. This obliged the contractors to modify the panel-laying portal cranes to accept the extra weight.
The design of dual-gauge turnouts posed a special challenge. All the three crossings are rigid and the use of switch crossings has been avoided. All turnouts have their curved leads running through over the crossing gauge faces. Both these principles were new to South Asian practice and had to be designed from scratch. Turnouts for both the main contractors are being supplied by Rahee Industries of Kolkata and have been designed by Dr M Seshagiri Rao, their consultant.
All the steel girder bridges have steel H-beam channel sleepers to accommodate dual gauge. They are equipped with Rahee Patent rail-free fastenings to suit the Pandrol clips. The rail can be run through without transmitting the temperature forces to the girder.
Traffic on both gauges will be moving by December this year, with the introduction of through trains between Joydebpur and all the important towns in the west of the country.
- CAPTION: Broad-gauge trains terminating at Bangabandhu East have been running over the bridge since 1998
- CAPTION: Track panels being laid by Ircon in western Bangladesh. The heavy sleepers required modifications to the panel lifting equipment
- CAPTION: A four-rail configuration was used for the track across the bridge
- CAPTION:Dual-gauge turnout laid by Travaux du Sud-Ouest. Modern concepts of curved switches, curved crossing gauge face and welded crossing frogs are being used for the first time in Bangladesh