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Home » Blog » Concrete, Steel, Plastic Culverts
Concrete, Steel, Plastic Culverts
posted by Florin Nicolae
September 25, 2010
A culvert is a covered structure that conveys a flow under a road, railroad or other obstruction. Culverts are mainly used to divert stream or rainfall runoff to prevent erosion or flooding on highways. They are constructed from a variety of materials and are available in many different shapes and configurations.
Culvert type selection depends on the following factors:
- hydraulic capacity;
- fill height;
- service life;
- execution speed;
- cost;
- maintenance;
- terrain;
- roadway profile;
- foundation condition;
- shape of the existing channel;
- fish passage.
Hydraulic Capacity
In terms of hydraulic capacity, culverts must meet the following conditions:
- ensuring the transition flow calculation;
- water level upstream the culverts mustn't exceed both the maximum flood level of the objects and the safety level of the road platform;
- the flood duration for agricultural lands mustn't be greater than the duration from which the plantations from flooded area are beginning to suffer;
- water speed in culverts and downstream of them mustn't exceed the maximum speed allowed of terrain nature or river bed protection.
Fill Height
Another step in choosing the right culvert is to verify that the depth of backfill is in between the recommended minimum and maximum fill heights. Minimum fill height is defined as the vertical distance measured from the top of the culvert to the bottom of the pavement or shoulder surfacing at its lowest point. Maximum fill height is defined as the vertical distance measured from the top of the culvert to the top of the pavement at its highest point.
For all the culverts the minimum fill height is 30cm or higher. Exceptions are special box culverts designed to carry traffic on the top slab.
If additional room for cover is needed a good alternatives to circular shapes of the culverts are arch and horizontal elliptical. This two shapes provide the same hydraulic flow with a smaller hight of the culvert.
The maximum fill height depends on the thickness and diameter of the culvert. A culvert with a bigger thickness or a smaller diameter can support a higher fill. So, the culverts can be dimensioned to support almost any filling hight.
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