Drainage Construction Procedure
If water exists on or underneath the roadway, the roadway gets damaged significantly. Water in roadway leads to rutting, cracking, potholes, corrosion, washouts, heaving, flooding, untimely failure of the roadway.
To get rid of these issues and keep the longevity of the roadway, a proper drainage system is required.
A drainage system should comprise of various components with perfect functionality and should be maintained in a perfect manner.
- Surface drainage
- Subsurface drainage
- Culverts, ditches and gutters
Road surface drainage is necessary for the drainage of storm water runoff from the road surface and the surfaces close to road construction.
Various components are utilized to prevent or hold this outflow and allow smooth discharge to a proper receiving place.
Due to the rainfall onto road surfaces, water is discharged to the lower point and while passing across the road surface, a layer of water with variable thickness is created.
This water becomes problematic for the vehicles. Splash and heavy spray are thrown up by movable vehicles which minimize visibility whereas the water on the pavement minimizes the friction among the tires and the road surface.
Design of the components for this overflow should sufficiently maintain the safety and convenience of road users along with pedestrians and safeguard adjoining properties & road pavement from damage.
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A crown should contain adequate slope from the pavement centerline to the edge so that the water is discharged properly from the roadway surface.
If the slope remains very flat, water is accumulated on the surface and passed through joints and cracks into the pavement or under the surface.
It results in cracking of pavement and forming potholes. The water that is not discharged through the roadway, creates a safety risks to motorists.
To facilitate sewerage, shoulders should be flush with the adjoining roadway, slope a little from the roadway, and does not contain any erosion or secondary ditches. Earth shoulders should be cut from time to time.
Slopes refer to the ratio of the run to the rise. The degree of foreslope and backslope is defined with design standard and local conditions (e.g. cohesive soils, or right of way). Based on local conditions, the slope should be constructed steeper or flatter.
A subsurface drainage system discharges water from under the pavement to proper drainage features like ditches or storm drains.
The objective of subsurface (or subsoil) drainage is to check the moisture content of the pavement and the adjacent material to retain the strength of pavement and longevity during the design life.
Under drain/edge drains
A well-organized system of transverse and longitudinal drainage pipes perfectly prevent and carries water from the granular layer to edge drains. Edge drains are formed under shoulders, longitudinally close to the pavement.
Edge drains are built up throughout roadway construction where a perforated pipe is placed in a parallel to roadway, that is then backfilled with an open-graded aggregate.
Culverts form drainage under driveways, roads, slopes and adjoining areas.
Their grade and direction should match to that of the water they are carrying.
Culverts should be properly maintained when the flow line and the design slope from inlet to outlet is still available.
No sections are arranged and all joints are tight and not detached.
The curtain walls are not uncovered and the downstream channel is not affected with corrosion.
A gutter refers to a depression that runs parallel to a road constructed to collect rainwater passing along the street & change it into a storm drain.
The purpose of a gutter is to reduce storing of water on a street, facilitating the passersby to drain devoid of pass through puddles and minimize the risk of hydroplaning by road vehicles.
With the existence of a curbstone, a gutter is created by the convergence of the road surface and the vertical face of the sidewalk; otherwise, a designated concrete gutter surface exists.