Highway drainage

This is about highway drainage.

1. HIGHWAY DRAINAGE

2. Highway drainage - the process of removing and controlling excess surface and subsurface water within the roadway or right of way. Types: 1.surface drainage(removal & diversion of surface water from the roadway & adjoining land ) 2.subsurface drainage(diversion or removal of excess soil-water from subgrade ) Highway Drainage

3. Excess moisture in soil subgrade causes lowering of its stability If any improper drainage system, flow of surface water across the road & shoulder and along slopes should cause erosion If stagnant of water, it causes diseases loss of money, human life Effects of drainage

4. The side drain should have sufficient capacity and longitudinal slope to carry away all the surface water collected from the roadway Lowering of moisture content of soil The pavement should be higher than water table To control the capillary rise Maintenances of highway drainage

5. Cross slope or camber The road side drains Cross drains Components of surface drainage system

6. Water from the pavement surface & shoulders is first drained off within the help of cross slope or camber Rate of slope depends on : Type of the pavement surface Amount of rainfall in a region Recommended range of camber : For earth road : 1 in 25 or 4% For bituminous road : 1 in 60 or 1.7% For earth shoulders: 4 to 5% Cross slope or camber

7. Cross slope or Camber

8. The road side drains of highways are generally open or unlined or kutcha drains of trapezoidal shape If provided to parallel to road alignment – longitudinal drains On plain terrain with embankment –provided on both sides of toe of embankment On sloping terrain( cross slope<4%)-provided on one side only. Road side drains

9. Road Side Drains

10. The water flowing along the road side drains are collected by suitable cross drains through cross drainage structures(CD structure) It is collected from natural valleys & streams and disposal off to the natural water course Different types of culverts(CD structure) : slab, box & pipe culvert If the width of river or stream > 6m – CD provided is called minor bridge If the width of river or stream > 60m- CD provided is called major bridge Cross drains

11. Cross drains

12. to keep the variation of moisture in subgrade soil to a minimum Components: Lowering of Water Tables Control of Seepage Flow Control of Capillary Rise Sub-surface Drainage

13. The highest level of water table should be fair below the level of subgrade, in order that the subgrade & pavement layers are not subjected to excessive moisture. From practical considerations- water table > 1.0 to 1.2m below the subgrade water table at ground level -1.2 to 1.5m above the ground level Lowering of water table

14. If the soil is relatively permeable, it may be possible to lower the high water table by construction of longitudinal drainage system with drain pipe and filter sand If the soil is relatively less permeable, the water table can controlled by construction of longitudinal drainage system with transverse drains( at particular interval)

15. When the general ground & impervious strata below are sloping ,seepage flow exist If depth of seepage zone < 0.6 to 0.9m longitudinal pipe drain may be constructed to intercept the flow Control of seepage flow

16. Control of seepage flow

17. If water due to capillary rise is less, it is possible to solve problem by arresting capillary rise instead of lowering of water table Two methods of control Granular capillary cut off Impermeable capillary cut off Control of capillary rise

18. A layer of granular material provided between subgrade & highest level of subsurface Granular capillary cut off

19. An impermeable membrane or bituminous layer inserted in place of granular materials Impermeable capillary cut off