Construction Procedure of Surface Road Side Drainage-PART 1 (with picture)

Surface water ( i.e., rain water) that falls on the ground surface such as; open field, paved areas or road surface, roof tops etc are channeled to a main drain naturally or through a constructed channel which is referred to as drainage.

Procedure for construction of a common drainage (trench) (1m x 1m U drainage) (reinforced). includes;

I.      Marking Of Alignment:

The surveyor marked out the alignment for the trench to be dug.

II.      Digging/Excavation:

The surveyor marked out the dept of the trench to be excavated with a mechanical excavating machine.

For a 1m x 1m drainage, the mathematical process of obtaining the required dept is to sum together the dept of the required drain + base + blinding.

For dept:

 A drain of dept1000 mm, base of 150 mm and blinding of 50 mm.

Hence 1000mm + 150mm + 50mm = 1200mm (1.2 m)

So an excavation of 1200mm (1.2m) is required from the to level of the road surface.

For width:

A minimum of (2.5 x width) m is advisable.

 For a 1 m x 1m drainage,

Since the drainage internal width is 1m, using

   1.5  x width =

2.5 x 1m = 2.5m

2.5m width excavation minimum is acceptable to create space for construction work area.

III.      The next step after excavation of drainage is the CONCRETE BLINDING.

Blinding is done on the surface area in order to correct any irregularities in level of the bed of the excavated surface, and to provide a smooth, level and regular surface to receive the concrete base. It’s usually ±50 mm depending on the rate of regularity of the surface area. Concrete Grading C10 or C15 as sub-soil might require.

see concrete grading,

the blinding is a mass concreting and its advisable to spread to cover entire width of the excavated trench except where there is need for material management.

 IV.      Reinforcement (iron Rod) positioning.

For a 1m x 1m drainage, a 12mm U shape reinforcement (spaced between 150mm to 300 mm or as designed) is placed into position on the blinded surface but positioned at the centre of the base with the aid of concrete biscuit to create a concrete cover.

There should be concrete cover between the reinforcement and the base of the drain concrete base and the top of the drain wall.

Hence, Reinforcement Rod height needed should be;

1000mm (reinforcement height) + 75mm (base top conc. Cover) - 25mm (wall top concrete cover) = 1035mm (1.035m) .

NB: the center of the reinforcement base should be align with the centre alignment provided by the surveyor in order to have consistently uniform alignment.