Culverts are used to divert small water effluents and pass them under the road. Their use is more appropriate than the construction of a bridge.
General concept
Culverts are used to pass water from the top of the roads to the bottom. These include culverts, bridges, drainage systems. The latter are used to pass various channels under the roadway.
Culverts are used in cases where it is necessary to let small drainage systems (streams, drain water after rain or snow melt, and so on) under the road. The passage of water through pipes can be carried out continuously or periodically. Through such facilities, cattle passage or transport passage is sometimes organized.
The arrangement of culverts does not require narrowing the carriageway and changing the type of road surface. Backfill is arranged over the structure. The thickness of the layer of poured soil reduces the pressure on the structure from cars and softens their effect.
The use of pipes for water passage has its advantages:
- Installation of pipes takes place without damaging the subgrade.
- Pipe installation is cheaper than building a bridge.
- With a backfill layer thickness of more than 2 m, the effect on the construction of temporary loads from passing vehicles is minimized.
Pipe sizes
The diameter of the culvert depends on its length:
- If the length of the pipe does not exceed 2-3 m and the height of the embankment is less than 7.5 m, then the hole of the pipe is chosen equal to 100-150 cm.
- For embankments up to 1.5 m, the diameter should be 75 cm.
- Pipes within the ramps are 50 cm in diameter.
Under roads of categories 2-4, culverts with a diameter of 100 cm and a length of up to 30 m are allowed. If the diameter is 75 cm, the length of the pipe should not be more than 15 m.
Classification
Culverts are classified according to several parameters.
Depending on the material from which they are made:
- Polymer (from polymer concrete, polyvinyl chloride and polyethylene).
Several types of pipes are distinguished depending on the shape of the cross section:
According to the principle of the section:
In the cross section of the pipes can be one, two or more points.
The main elements of the pipe and their installation
Culverts consist of several elements:
Due to the presence of heads in the pipe, no whirlpools, vortices are formed, water flows out more slowly. Their presence prevents leaking water from eroding the embankment and washing away the foundation.
There are several types of heads:
- Gantries, which are constructed in the form of a perpendicular pipe retaining wall. This is the simplest design, but it has its drawbacks. It does not provide a smooth flow of water. Therefore, its use is recommended in cases with a small amount of water flowing at an insignificant speed. Gantry heads are used for pipes with a diameter of 50-75 cm.
- Bell-shaped. In addition to the wall, they have two openers forming a bell. The wings are located at an angle of 30 degrees to the pipe. Due to this, the flow of water gradually narrows.
- Collar, in which the extreme element is cut at the same angle as the embankment. A protective collar is installed along the contour.
- Streamlined in the section gradually narrow, which creates good conditions for the flow of water.
The pressure on the ground is evenly distributed due to the foundation on which the pipe is laid. It also prevents the shift of individual elements of the structure.
The following types of foundation exist:
- Without foundation (natural foundation).
- Soil pillow created artificially.
- From individual reinforced concrete elements.
The choice of foundation type depends on the diameter of the pipe, the height of the embankment and the geological conditions.
The culvert is located strictly perpendicular to the axis of the road. This gives a minimum pipe length. In some cases, it is recommended to install the structure in the direction in which the stream flows. This reduces the likelihood of whirlpools. In such cases, the construction of culverts in other directions is allowed.