What are Curb and Gutter?
Kerb (sometimes called Curbs) is one of the components of the road provided at the edges of the carriageway to provide barrier and safety so that vehicles cannot cross it. Curbs are usually made of either stone or concrete of high strength and have certain more elevation than the road carriageway.
Gutters(sometimes called channels) are build as part of curbs adjacent to the carriageway for the surface water flow through it.
Usually, the curb and gutter are built together simultaneously so, the two components are always named together. Curbs and Gutters are usually used in city areas and urban towns roads and streets more popularly.
They are rarely used on rural roads as the water can freely discharge into surrounding fields and open lands. And moreover, it increases the cost, thus are neglected for rural streets which have very less traffic activity.
However, the rural streets having proper drainage and sanitary system having manholes, the Kerbs and Gutters are preferred for design.
Kerb should have a minimum height of 150 mm and should have a minimum strength of 20 MPa and can also be made up to 30MPa for better safety. The drop curbs are used for ramps and visually impaired peoples at the place where the cross is to be made for example at zebra crossings.
And Gutters are provided with the pipe as a culvert for smooth ramp and without disturbing the water flow too. For maximum capacity or hydraulic efficiency, the wetted perimeter of the gutter should be kept minimum which can be made possible by making the full flow in a semi-circular gutter.
The structure can nearly achieve in a site known as spoon drains. However, it is too cumbersome and difficult to achieve and work with such structure at the site, and thus triangular drains with V-shaped or the shape of Tick mark are made for easy work known as catch drains or Tick drains or V-shaped drains.
The gutters are suitably open at the catch pits or manholes of the sewer system. And moreover, there is the provision of the opening at the curbs to cross the water of gutters if such sewer system located inside the area of footpaths.
Purpose of Curb
Kerbs are located at edge of the roads bounding the pavement material of road. Thus they prevent the lateral spread and loosing of the paved material from street and provide strength at the edge
Kerbs and Gutters form the proper drainage system of road run off water. The high kerb prevent water of street to spread out of surrounding area of pedestrian walk and gutter provide direction and exit of such run off water to proper manhole and catch pits
Kerb and gutter prevent the seepage of the surrounding watery through the cracks and voids that may present at edge of pavement. And as we know water is biggest enemy for the asphalt pavement, it thus increase the period of service for asphalt pavement by sealing such voids and stopping the seepage.
Kerb helps to create level difference between pedestrian walk path and carriage way. Thus vehicles cannot cause harm to the people walking on footpath even accidentally.
Kerb acts as barrier, so vehicles can’t just cross through it. So, one of the purpose of kerb is to use as barrier and thus can also be used to create diversion, traffic island and mark safe boundary on hilly roads.
Kerb also facilities the safe measures for visually unable person to get off from footpath to carriageway unknowingly.
Most of the times, kerbs are painted with alternative black and white colour or yellow-black colour so they provide longitudinal edge marking for drivers.
Types of curb and gutters
A) On basis of the function
1) Barrier kerbs: These kerbs have a slope of 4 vertical to 1 horizontal at face adjacent to the carriageway. Their main purpose is to completely unable to move vehicles of carriageway over it. The kerbs are used in hilly roads with the highly sloped area.
2) Semi barrier kerbs : These kerbs are similar function to barrier kerb but these kerb have vertical face till half of the height of kerb and from there slope 1 vertical to 1 horizontal is maintain. They are generally used in urban street and roads.
3) Semi mountable kerbs : Semi mountable kerbs have also vertical face till 1/3rd of the height of kerb and from there slope of 1 vertical to 3 horizontal is maintained. Such kerbs are designed with purpose of emergency exit of the vehicle like firetruck and ambulance and ramps.
4) Mountable kerbs : These kerbs are designed with purpose of easy movement of vehicles over it. Thus they are also called rollover kerbs as the vehicles can easily cross when needed. They are kept near the parking area, open ground area etc.
5) Mower kerb : Highly decorative shaped kerbs used in gardens and lawns to increase aesthetic value.
B) On basis of shape
- Rounded kerbs
- Bull nosed kerbs
- Square kerbs
- Half battered kerbs
- Splayed kerbs
C) On basis of the construction method
1) Precast kerbs: These kerbs are precast in form of blocks and then later on used as masonry units joining along with mortar. They are easy method of making kerb at end of the pavement.
2) Monolithic kerbs: These kerbs are generally RCC kerbs, generally made along with rigid pavement and bridges monolithically.
3) Cast insitu kerbs : These are kerbs built along with gutter either manually or by the use of machineries at the site. Such kerbs need to be cured for higher strength at site.
4) Stone kerb : These are the traditional method of making road. The bigger stone with higher strength are first laid on the edges of the road and then only remaining pavement materials like base sub base are laid. Such kerbs can be seen in roman roads and traditional old roads.
5) Asphalt kerbs : They doesn’t have much strength but are used for aesthetic beauty.
Construction Process of Curb and Gutter
Curbs can be constructed by either precast curbs masonry arrangements or by the cast-in-situ method. Further cast in-situ is either done manually or by the machinery plant along with the gutter.
However there is general procedure for all types of Kerb and Gutters construction. It can be listed as:
The edges of the road are excavated first and then marked for the kerbs.
The base are stabilized with rammers or tamping the soil.
Then the kerbs are first placed. If the kerbs are masonry unit concrete blocks then they are constructed as mini wall of single layer joining one another with mortar. If they are cast insitu type then the formwork are made for kerb and then concrete is poured over it.
The kerbs are then back filled with the soil. And on the edge adjacent to carriageway is stabilized with rammers for gutter.
The slope for gutter should be maintained as required so that there is proper water flow.
Then, over the compacted layer, the brick or stone soiling is done.
The gutters can also be used as precast slabs for the spoon drains or it can be casted insitu. But due to difficulties in maintaining round shape, the gutter are generally design triangular with kerb face. It can be either V shaped or Tick mark shaped. For such Gutters the soiling and levelling is also done as required slope.
If the gutter is cast insitu, then the firm work is placed. And plain cement concrete of grade greater than 20MPa is laid over it maintainng required gradient.
The gutters are suitably open to the catch pits or drainage or manholes with the steel Gratinhs
If the drainage lies inside part of the kreb or footpath then special kerbs having hole are use to cross the water to drainage.
The kerbs are then painted with the colours or can be marked with highlighting reflective for more road safety.
Advantages of Curb and Gutter
1) They increase the aesthetic beauty of the road
2) It helps to decrease the seepage through the lateral confinement of the pavement layer.
3) Curb and Gutter Stabilize the later pavement layer after more vehicular movement to road.
4) Provide lateral supports to the pavement layer and reduce the disintegration of paving layers on the edge.
5) Kerbs creates barrier and thus provide the aligned path to keep vehicle in track.
6) They decrease vehicular and pedestrian conflicts and accidents.
7) Kerb provide boundary region for roads, parking, garden and lanes.
8) Gutter swept all the surface water runoff safely through it without affecting the slippery effect on the carriageway.
9) Kerb raise the pedestrian pathways.
10) Kerb and gutter increase the road safety.
11) Kerb with the reflective lights and material help in easy driving.
I hope this article on “Curb and Gutter details” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Rajan Shrestha