Padma Multipurpose Bridge Project

Embankment crest, back slope and key-in28. The crest is 10 m wide and is covered with concrete blocks to provide a flat surface. The backslope on the landward side slopes down at 1V:3.5H and is extended or "keyed into" the floodplain overa width of 10 mSpecial features29. To permit access to the river at pre-defined locations, the wave protection will include steps thatreach down to low water level. Boat access will be possible, as the typical low water level of El. 1.8 mPWD will provide more than 2 m of draft above the berm at El. -1 m PWD.30. A number of smaller distributaries take off from the bank of the South Channel, to accommodatewhich the south approach road includes several floodplain bridges of up to 280 m in length. The offtakezones at the bank will be specially treated to provide fixed cross sections through the riverbankprotection: a channel will be formed with protection extending some 100 m inland to avoid localoutflanking and erosion of the riverbank. Figure 2-8 shows an example of a distributary take-off fromthe upper slope, with varying concrete block thickness.Figure 2-8: 3-D presentation of sample off-take for distributaries. Wave protection elements includingstaggered and projecting concrete blocks.2.3.3 Approach Roads31. The following design details for the approach roads are considered: 2.3km long approach road in the Mawa side and 12.8km long approach road of 23.6m width inthe Janjira side totaling 15.1km; An approach road viaduct of 2.032km for Mawa side and of 1.915km for Janjira side; In the Mawa side the existing two-lane road will be widened to a four-lane approach road; In the Janjira side new approach road will be built with 6 bridges, 14 culverts, 7 underpasses,service roads and 11 road-junctions;32. Approach roads on both sides: The total width of each road is 23.6m and the vertical elevation is13.25m PWD (Public Works Datum). The design speed adopted in the approach road is 100km/h. Theapproach road has 2 lanes in each side with lane width of 3.65m and 2m hard shoulder and 0.5mInner Marginal Strip (IMS) in each direction. The road is designed with a 4m central median with a30cm up-stand to prevent vehicles crossing this central reserve. The typical cross-section of road ispresented in Figure 2-9. In addition, the 4m median feature will allow the provision of a right-turn(restricted use) lane at appropriate locations along the project road. It also fulfills the desired roadsafety requirements of providing the widest central median. The purpose of an approach road viaductis to connect the approach road to the main bridge allowing under-passing of peoples, goods,vehicles, etc. The span of road viaduct is 30m.33. Small bridges on approach road at Janjira side: The approach road on the right bank of the Rivercrosses over five minor inland waterways which are used as local navigational channels duringmonsoon. In addition, a bridge will be constructed on paddy land in the flood plain on hydrologicalimpact consideration of the road. As such, six bridges will be constructed over these locations toensure free passing of country boats and River flood water for offsetting hydrological impacts.2-14