Culverts are used to divert small runoffs of water 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 pass small drainage systems under the road (streams, draining water after rain or snow melt, and so on). The passage of water through pipes can be carried out continuously or periodically. Such facilities are sometimes used to organize the passage of livestock or the passage of vehicles.
The installation of culverts does not require narrowing the carriageway and changing the type of road surface. A backfill is arranged over the structure. The thickness of the poured soil layer reduces the pressure on the structure from cars and softens their impact.
The use of pipes to pass water has its ownbenefits:
Pipe installation proceeds without damaging subgrade
Piping is cheaper than building a bridge
When the thickness of the backfill layer is more than 2 m, the impact on the structure 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 pipe opening is chosen equal to 100-150 cm
For an embankment up to 1.5 m, the diameter should be 75 cm
Pipes within ramps are 50 cm in diameter
Under the roads of 2-4 categories it is allowed to use culvert pipes with a diameter of 100 cm and a length of up to 30 m. If the diameter is 75 cm, then the length of the pipe should not exceed 15 m.
Classification
Culverts are classified according to several parameters.
Depending on the material from which they are made:
Concrete
Polymer (from polymer concrete, PVC and polyethylene)
Reinforced concrete
Stone
Metal
Fiberglass
There are several types of pipes depending on the cross-sectional shape:
Round
Arched
Elliptical
Rectangular
Trapezoid
Ovoid
Triangular
According to the principle of the section:
Non-pressure
Pressure
Semi-pressure
There can be one, two or more points in the cross section of pipes.
The main elements of the pipe and their installation
Culverts consist of several elements:
Entrance cap
Pipe links
Outlet cap
Due to the presence of tips in the pipe, whirlpools and eddies are not formed, water flows out more slowly. Their presence prevents the flowing water from eroding the embankment and washing away the foundation.
There are several types of headbands:
- Portal, which are built in the form of a retaining wall perpendicular to the pipe. This is the simplest design, but it has its drawbacks. It does not provide smooth water flow. Therefore, its use is recommended in cases with a small amount of water flowing at low speed. Portal tips are used for pipes with a diameter of 50-75 cm.
- Bell-shaped. In addition to the wall, they have two openings 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 off at the same angle as the embankment. A protective collar is installed along the contour.
- Streamlined in section gradually narrow, which creates good conditions for the flow of water.
The pressure on the ground is distributed evenly due to the foundation on which the pipe is laid. It also prevents the shift of individual elements of the structure.
There are the following types of foundation:
Without foundation (natural foundation)
An artificial soil cushion
From in-situ concrete
From individual reinforced concrete elements
The choice of foundation type depends on pipe diameter, embankment height and geological conditions.
The culvert is located strictly perpendicular to the axis of the road. This gives the minimum pipe length. In some cases, it is recommended to install the structure in the direction in which the flow flows. This reduces the likelihood of whirlpools. In such cases, the construction of culverts in other directions is allowed.
