culvert design and installation

 CULVERT INSTALLATION
Culverts by definition  are drainage structures used  to convey flood waters along  the  road side drains.There are two main type of culvert depending on  location and type of  inlet,namely;access culvert and cross drain culvert.
Access culvert are  located parallel to the road center-line while as the cross culverts are installed perpendicular  to the road center-line.
Cross culvert mostly has a box type of inlet and usually sited at river gauge to convey water from  left-hand to right-hand side of the road of vice-versa.
For a standard road of 5.4 meter cross section a 9M DIA or 6 M DIA culverts are preferred.


cuvert installation procedure ( 6 M diameter  culvert)
A trench 1 m length and 102 centimeter depth is dug  occasionally offset 30cm from  a 1 m meter ditch.
A gradient of 2-4% is required to allow the water flow without  head erosion taking place.
The gradient is established  with respect to the existing crown camber of the road using line and level as a control tool.
Before laying out culvert ring  blinding of the trench is done with a maximum depth of 0.15Meters.Batching of 1:3:6 is preferred.curing is done for 2 days  to allow setting to take place.
Next the rings are laid  in such a way they form a continous conduilt  to allow the water to flow with a unifoerm velocity.the ring are the covered with soil or concrete depending on the type of vehicles moving along such road.For heavy commercial vehicles concrete is prefered.