07-ROAD DRAINAGE



ROAD DRAINAGE

An effective drainage system is required to minimise access of water into the pavement layers and prevent damages to pavement resulting from the saturation of the subgrade or fill immediately below. The road drainage should be effective in disposing the surface precipitation and controlling the underground seepage. For the design of drains, the IRC publications SP: 42 & SP: 50 can be referred. Damages caused to the road by inadequate drainage are:

  1. Reduction in bearing capacity of the subgrade soil due to the presence of water, leading to complete failure of the pavement.
  2. Reduction in the design strength of pavement layers such as stabilized soil, water bound macadam etc., due to the ingress of water.
  3. Potholes, rutting, waviness and corrugation of the bituminous pavement layers.
  4. Erosion of shoulder and pavement edges due to the flow of surface water.
  5. Loss of soil from the subgrade and fill layers below the pavement due to seepage of water.
  6. Erosion of slopes of fill/cut or hillside due to surface water.

Suitability of different types of lining in side drains

   Type of lining

Brief description

          Suitable for

Unsuitable for

 Turfing

Turfing is useful in

humid area for

preventing erosion.

Triangular drains having

4:1 to 3:1 slopes.

Rectangular,

Trapezoidal

drains since

maintenance is difficult.

 Stone/brick

Stone/brick masonry

can be laid dry or

bedded in concrete

with joints filled with

cement mortar.

When drains are

required to carry a large

amount of debris or if

the velocity of flow is

high.

In known

unstable area.

Concreting

-

As above

As above.

Stone slab lining

-

For triangular section

drains and in other

section in combination

with masonry/

concreting and in areas

where flat stone is easily

available.

 

Boulder pitching

-

For areas with stable

slopes

In unstable loose

strata.

Bituminous treatment

It is primarily quick

sealing of the sides

and base impregnated

with bitumen cutback

or emulsion 10 cm to

15 cm depth.

Used in conjunction

with boulder pitching in

catch water drains for

prevention of seepage

flow

 

Table: Gradation of material for drainage layer

IS sieve designation

% by weight passing the IS sieve

75 mm

100

53 mm

-

26.5 mm

55-75

9.5 mm

-

4.75 mm

10-30

2.36 mm

-

425 mic

-

75 mic

<5

RELATED CODES :

1.   IRC-SP: 20      Rural Roads Manual - published by Indian Road Congress, New Delhi 2002.

2.  Manual of specifications and standards for two lining of highways through PPP – published by the Planning            Commission, Government of India.

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