2. Highway drainage is a process of removing and
controlling excess surface and sub-soil water
within the right of way.
It includes interception and diversion of water from
the road surface and sub grade.
3. Excess moisture in soil subgrade causes considerable lowering
of its stability.
Increase in moisture cause reduction in strength of many
pavement materials like stabilized soil and water bound
Sustained contact of water with bituminous pavements causes
failure due to stripping of bitumen from aggregates like loosening
or detachment of some of the bituminous pavement layers and
formations of pot holes
Excess water on shoulders and pavement edges causes
4. Adjoining land
Cross drainage works
Highest flood level
Underground source of water 4
5. Removal and diversion of surface water from the road
way and adjoining land is termed as surface drainage.
Diversion and removal of excess of soil water from the
subgrade is termed as Surface Drainage.
6. 1. By Longitudinal side drains.
2. Catch basins and Inlets in urbanareas
3. Providing damp proof course
4. Providing proper camber
5. Providing sufficient slope to the sides
6. Keeping the level of carriage way at least 60 cm above the HFL.
8. It is necessary to provide side drain on one side or both
sides, when road is constructed in embankment.
Side drains should be at least 2.0 m away from bottom
edge of an embankment.
Depth of side drains is kept 1.0 to 1.5 m to prevent
the entry of drain water into the embankment.
11. Catch basin is a structure like chamber constructed on a
Water from pavement surface is collected in catch basin
and discharged to the sewer line.
The catch basin (catch pit) is provided with grating to
prevent the entry of rubbish into the drainage system.
12. Inlets is a concrete box with grating either at the top or in the
13. Removal or Diversion of excess soil-water from sub-grade is
termed as sub-surface drainage.
When road is in cutting and water seeping from sides.
When road is near the foot or hill and is likely to be damaged by
water flowing down the hill.
When road is passing through plain area and water is likely
to accumulated on sides.
Where water rises up to sub-grade by capillary action.
Where sub-grade soil is affected by the drain passing near the
15. In order to that the sub-grade and pavement are not
subjected to excessive moisture the water table should kept
at least 1.0 to 1.2 m below the sub-grade.
In places where water table is high to take the road formation
on embankment of height not less than 1.0-1.2m is the best
But When the formation level is at or below the general ground
level it is
necessary to lower the water table.
16. (a) If soil is relatively permeable, it may be possible to
lower WT by constructing longitudinal drainage trenches
with drain pipe and filter sand and top of trenches is
covered with clay seal
The depth of trench depend on:
(i) The required lowering of water table
(ii) distance b/w the drainage trenches
(iii)Types of soil
18. (b) If the soil is relatively
less permeable, the
lowering of groundWT
may not be adequate.
Hence in addition to the
traverse drains have to be
installed at suitable
intervals in effectively
drain off the water.
19. When the general ground as well as impervious
strata below are sloping, seepage flow is likely to
If seepage zone is at depth less than 0.6-0.9 m
from sub-grade level, longitudinal pipe drain in
trench filled with filter material and clay seal may
be constructed to intercept the flow.
21. If the water reaching the sub-grade due to capillary rise is likely to
be detrimental, it is possible to solve the problem by arresting
the capillary rise.
It can be done by following methods:
(a)A layer of granular materials of suitable thickness is provided
during the construction of embankment, between the sub-grade
and the highest level of sub surface water table.
(b)Alternate method is providing the capillary cut off is by
inserting an impermeable or a bituminous layer in place of