Padma Multipurpose Bridge Project

2.3.5 Railway43. At the initial stage, railway on the bridge connecting two stations at the bridge ends wasconsidered. However, the scope has been revised to provide the future provision of the railway. Thetotal length of the future railway structure is 15.85km including those over main bridge (6.15km),railway viaducts (2.789km at Mawa side and 2.899km at Janjira side) and approach railway (2.45kmat Mawa side and 1.7km at Janjira side) connecting two stations at bridge ends. The current scopecovers the the provision of railway in lower deck of the bridge including railway viaduct. The purposeof long railway viaduct is to allow rails gradually ride the main bridge at a very soft gradient of 0.5%from the railway line that comes along the approach roads, along with free-passing of vehicles andothers under the viaducts. The superstructure will be built of simply supported 1,600mm deep posttensionedpre-cast concrete I-Girders with a cast in-situ composite deck slab.2.3.6 Utility Crossings44. The main utilities to be accommodated include the power transmission line (400kV) and the gasmain. The gas main is simply supported within the truss with vertically orientated loops toaccommodate the necessary movements. At the two transition piers, the gas main is brought down toground and is carried underground away from the bridge structures. The bridge will be “gas mainready” as the gas main will not be installed for some time after construction is completed.45. The power transmission line is not fully resolved yet. Again the power transmission line isunlikely to be provided within the first 8 years of the bridge life. The Consultant is still addressing howbest to accommodate the transmission line. One option is to install the 6 solid insulated cables withinthe truss and looking at the cost involved and any other effects such as close proximity to the rail line.This is currently how it is shown on the main bridge cross-section drawings (Figure 2-4). For thiscase, the power transmission line would be taken down to ground at the transition piers and it isexpected that there would be some form of transformer complex away from the bridge which wouldallow the cables to transfer to conventional steel lattice towers away from the bridge. The other option(more likely) is to provide separate piled platforms further downstream from the bridge which wouldsupport conventional steel lattice towers. Six platforms would be required in the river. The bridgecontractor could be requested to install these piled platforms during the construction contract as hewould have the suitable piling equipment. Alternatively, the Consultant could make a cost provisionand the power authority could elect to manage the whole process at a later date.2.3.6.1 High Pressure Gasmain46. A 30in diameter high pressure gasmain on the bridge is considered with a separate corridor.Pigging system by installing scrapping trap stations, installation of shut off valves with ventingfacilities, expansion loops along with the gas pipeline to accommodate expansion and contraction ofabove ground pipeline, cathode protection (CP) system to protect pipeline corrosion, and SCADAfacilities at both end of the pipeline will be provided. In addition, necessary safety, operation andmaintenance facilities will be considered during design, construction, and operation phases as perNatural Gas Safety Rules, 1991 (as Amended in 2003) and other International Standards.2.3.6.2 High Voltage Power Transmission Line47. A 400kV high voltage power transmission line will be built, which will be either on the bridge orrun parallel and away from the bridge with the following features:The total length of the line is assumed to be 6.5kmThe new transmission line would consist of self supporting towers, 6 towers in the middle ofriver and 2 on either side on the bank. Nominal span of 830mThe height of river crossing towers would be 100-105m all, with based width at the foundationlevel to be around 20-25m. These towers would provide a clearance of 18.65m above thewater levelThe river crossing towers would be provided with climbing ladders with a fall arrest system.Since the total height of the structures is above 80m, the climbing ladders shall be furnishedwith work platforms at 20m intervalsStandard I-string suspension insulators would be usedTwo anchor towers on either side of the line would be installed on the bank with the terminalarrangement.2-18