Culverts

CULVERTS

Culvert is a small bridge of a span of less than 6 meters. It is a drain or water course totally enclosed. It is constructed under a highway or railway track to allow water to pass from one side to another.

Types of Culverts

Culverts are broadly classified as Highway Culverts and Railway Culverts. The loading and structural details are different for these two cases. The number of Vents or Openings may be one or more than one, depending on the span of the culvert and the quantity of discharge of the drain water. Generally, the types of culverts are:

1. R.C.C. Slab Culvert

2. Pipe Culvert

3. Box Culvert

4. Arch Culvert

5. Steel Girder Culvert

1. R.C.C. SLAB CULVERT

See Fig. 15. R.C.C. Slab Culvert is similar to R.C.C. Slab Bridge.

Its superstructure consists of R.C.C. Slab which carries the Road Way (Floor). R.C.C. Slab is supported on Abutments or masonry walls on either side.

R.C.C. Slab Culvert is used where the Bed of the Canal is sufficiently firm.

It is economical up to a span of about 6 meters. These culverts are used for highways and railways.

2. PIPE CULVERT

See Fig. 16. When the drainage discharge is less, depth of flow is less and no defined channel is present, a Pipe Culvert is preferred. Generally, R.C.C. Non-pressure Pipes are used.

Minimum diameter of the pipe should be 600 mm for easy cleaning and to avoid blocking of vent by debris.

Pipe culvert is easy to construct and economical. Pipe is laid in position on the Concrete Bed. Earth filling is done around the pipe and it is compacted. The number and diameter of pipes used are designed by the maximum discharge passing through the culvert and the height of the embankment of the road.

3. BOX CULVERT

See Fig. 17. R.C.C. Box Culvert is made of Square or Rectangular Opening. It consists of one or more number of openings or vents for the flow of drainage water from one end to the other.

It has the Abutments (side slabs), Top and Bottom Slabs constructed monolithically.

Masonry openings are not preferred. Top slab of the box section is placed at the road level. Box culvert is suitable for a single span of 3 meters and double span of 6 meters.

Box culvert is constructed:

(i) if the soil is soft, (ii) if the load is spread over a wider foundation area, and (iii) if scour is likely to occur.

4. ARCH CULVERT

See Fig. 18. An Arch Culvert consists of Foundation, Abutments, Arch and Parapet Wall. Brick Arch Stone Masonry or Concrete Arches may be used. The size of the arched opening can be adjusted during construction to carry the required quantity of water. The abutments carry the thrust of arches. They are made of either masonry or mass concrete.

If the soil is poor and if there is a possibility for scouring, Spandrel earth filling is done and compacted above the Crown of the arch. Arch Culvert is suitable for short spans of up to 3 meters only.

5.  STEEL GIRDER CULVERT

See Fig. 19. It consists of Steel Girders, Wooden Sleepers, Abutments and compacted Earth Filling. Two Steel Girders are provided for the superstructure of the railway culverts. Steel girder culvert is constructed below the rail track.

Wooden Sleepers are laid between the steel girders and the rails. Earth filling is done and compacted as shown.