PAD - LGED

asphalt pavement. 40 mm asphalt surfacing would be used on a few heavily trafficked upazila
roads.
Concrete Surfacing
9. Besides flexible pavement, the concept of causeway could be introduced in Sunamgonj
district and other such low lying areas which are prone to flash floods. The typical concrete
pavement for causeway consisted of the following:
Table 9.5: RCC Causeway
Layer Thickness Materials
RCC slab 200 mm Crushed stone, sand, cement and steel
reinforcement
Sub-base 150 mm Stone chips
Improved sub-grade 250 mm Sand
10. Concrete surfacing based on rigid pavement concept could be used in some Union Roads
in Sylhet and other regions. The typical concrete pavement used on Union Roads consisted of the
following:
Table 9.6: RCC Pavement Union Road
Layer Thickness Materials
RCC slab 200 mm Crushed stone, sand, cement and steel reinforcement.
Improved sub-grade 150 mm Sand.
BRIDGE DESIGN
11. Bridges on UZRs will be designed to AASHTO H-20 to Loading. The following cost
effective design measures will be adopted:
• Avoiding high abutments by increasing waterway openings where necessary.
• Designing for efficient use of steel reinforcement
• Using return type, rather than splayed wing walls.
• Designing bridges for double lane traffic (5.50 m).
12. The decks will be designed to have a 0.6 meter clearance above the 50 year high flood
level on non-navigable rivers. On navigable rivers the clearance will be varied from 1.0 meters to
1.50 meters according to requirements. High water levels will be determined from hydrological
studies. However in practice many of these high flood levels will be determined following
discussions with local people and observing watermarks of previous floods on buildings and
other structures.
13. Bridge length exceeding 30 meters will be designed for 50 years flood level and bridges
length of less than 30 meters will be designed for 20 year flood level.
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