1. HIGHWAY DRAINAGE
Presented by
Aglaia

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 subgrade.

3. Excessmoisture in soil subgrade causesconsiderable
lowering of its stability.
Increasein moisture causereduction in strength of
many pavement materials like stabilized soil and
water bound macadam.
Sustained contact of water with bituminous pavements
causesfailure due to stripping of bitumen from
aggregates like loosening or detachment of some of the
bituminous pavement layers and formations of pot
holes
Excesswater on shoulders and pavement edges causes
considerable damage.

5. In clayey soil variation in moisture content causes
considerable variation in volume of sub grade.
High moisture content causesincreases in weight and
thus increasein stress and simultaneous reduction in
strength of soil mass.
Erosion of soil from top of unsurfaced roads and slopes
of embankment,
cut and hill side is also due to surface water.
In cold regions presence of water in the subgrade and a
continuous supply of water from the ground water can
causeconsiderable damage to the pavement due to
frost action.

6. The surface water from the carriageway and shoulder
should effectively be drained off without allowing it
to percolate to sub grade.
Surface water from adjoining land should be
prevented form entering the roadway.
Side drain should have sufficient capacity and
longitudinal slope to carry away all surface water
collected.
Flow of surface water acrossthe road and shoulders
and along slopes should not causeformation of cross
ruts or erosion.

8. Seepageand other sources of under ground water
should be drained off by the subsurfacedrainage
system.
Highest level of ground water table should be
kept well below the level of subgrade,
preferably by atleast 1.2m.
In waterlogged areasspecial precautions should
be taken

9. During rains,
• part of the rain water flows on surface
• part of it percolate through the soil mass as
gravitational water until it reaches the
ground water below the water table.
Removal and diversion of surface water from the
road way and adjoining land is termedassurface
drainage.
Diversion and removal of excess of soil water from
the subgrade is termed asSurfaceDrainage.

10. Methods of surface drainage
1.By Longitudinal sidedrains.
2.CatchbasinsandInlets in urbanareas
3.Providing damp proofcourse
4. Providing propercamber
5.Providing sufficient slope to the sides
6. Keepingthe level of carriage way at least 60 cm above the HFL.

11. A)Sidedrainsfor roadin embankment
-

12. It is necessaryto 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 1.5m to
prevent the entry of drain water intothe
embankment.

13. B)Sidedrainsfor roadin cutting

15. A) Catch basins

16. Catchbasin is astructure like chamber
constructed on asewer line.
Water from pavement surface is collected in catch
basin and discharged to thesewer line.
The catch basin (catch pit) is provided with
grating to prevent the entry of rubbish into the
drainage system.

18. Inlets is aconcrete box with grating either at the top or in the
side.

19. For aquick drainageit isnecessaryto ensure that shoulder
surface is properly slopedand free from irregularities and
depressions.
In impervious type, it is practiced to extend the subbasecourse
with drainageacrossthe shoulderupto side drain.
Alternatively we canprovide cont layer of 75-100mm thick laid
under the shoulder at the bottom layer of sub baseabout 150
mm thick extended upto theedge.
The pavedshouldershould be at least 0.5%steeper then
camber subjectedto min of 3%

20. The unpaved shoulder should be further 0.5%
steeper along the horizontal curve,Shoulder on
inner side of the curve should have slope steeper
than that of pavement.
On the outer side, the shoulder should be made
to drain away from the pavement, alow rate of
super elevation are provided.
On the other hand, where higher rate of super
elevation, the outside shoulder are kept level or
rounded.

24. Except for amedian less than 5m wide, it is not
desirable to drain the median areatowards the
pavement surface.
 1.2 - 1.8 m wide median –Provided with kerbs
and always paved.
 1.8 - 5 m wide median – Usually turfed and
crowned so that surface water could run
towards the pavement maybe with or without
kerbs.

25. If carriage way slopes towards the median, central
drain maybe made to carry the runoff and slope
shouldnot be steeper than 6:1.
When the median hasonly earthen surface, it
should not be crowned because it can result in
soil particles being carried to the pavement
surface making itslippery.

27. Removal or Diversion of excess soil-water from
sub-grade is termed as sub-surface drainage.
The changein moisture of sub-grade are causedby
the following
 Fluctuations in GroundWaterTable
 SeepageFlow
 Percolation Of RainWater
 Movement of CapillaryWater
In sub-surface drainage it is practiced to keep the
variation of moisture in sub-grade to a minimum.

28. Lowering of Water
Table
Controlling Seepage
Flow
Controlling Capillary
Water

29. In order to that the sub-grade and pavement are
not subjected to excessivemoisture the water
table shouldkept at least 1.0to 1.2m below the
sub-grade.
In places where water table is high to take the
road formation on embankment of height not
less than 1.0-1.2mis the best approach.
ButWhen the formation level is at or below the
general ground level it is necessaryto lower the water
table.

30. (a) If soil is relatively permeable, it may be possible
to lowerWTby 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) distanceb/w the drainagetrenches
(iii)Types of soil

32. (b) If the soil is relatively
lesspermeable, the
lowering of ground WT
may not be adequate.
Hence in addition to the
longitudinal drains
traversedrainshaveto be
installed at suitable
intervals in effectively
drain off the water.

34. When the general ground aswell asimpervious
strata below are sloping, seepageflow is likely to
exist.
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.

38. 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 canbe done by following methods:
(a)Alayer 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 abituminous layer in
place of granular blanket.

40. Thesizeandspacingof the sub-surface drainagesystem
depend on the
quantity of water to bedrained off, the type of soil and
type of drain.
The filter material usedin sub-surfacedrains should be
designedto have sufficient permeability offering
negligible resistance to the flow.
And alsoresist the flow of the fine foundation soil
resulting in soil piping.
TheSteps areas follows:
Draw grain sizedistribution curveon log scale%passingvs.
particles size for the foundation soil.
Find the valueof D15sizeof foundation soil.

41.  Thesizeof filter material should be 5times more than the
sizeof
foundation soil
 D15of filter/D15 of foundation >5
Tofulfill the condition to prevent piping.
 D15of filter/D85 of foundation <5
Henceplot apoint represent the upper limit of D15sizeof
filter given by 5D85of foundation.
Find the sizeof the perforation in the drain pipe or the gap
in the open jointed pipes andlet this be =Dp
Plot apoint representing D85sizeof filter given by the size
2Dp.
TheShadedarea thus obtained represents the region within
which the grain sizedistribution curveof satisfactoryfilter
material shouldlie.

43. In caseof sub-grade subjected soil water to soakingcond.,
capillary rise, and in extreme cond. Even flooding for
prolonged periods is termed as water loggedareas.
In such areasconstruction and maintenanceof road is a
problem.
Methods adopted to Overcome
 Raisingthe road level by constructing embankment
 Providing acapillary cut off to arrest capillary water
 ProvidingCementConcrete Block
 Depressingthe sub surface water level by drainage
system

44. Thank you
Lintels
For more…. Mail to aglaiaconnect2018@gmail.com