Quality Assurance Handbook for Rural Roads Volume-I - pmgsy

1100: PIPE CULVERTS
A. Methodology
A 1 Excavation for pipes
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Quality Assurance Handbook for Rural Roads
1. Lay the pipes in shallow excavation of natural ground or in open trenches cut in existing
embankments taken down to required level.
2. For embankments of height of fill more than 3 m, or three times the external dia of pipe above bed
level, construct the embankment to the level above the top of the pipe (equal to external dia of
pipe) and width not less than five times the dia of pipe. Lay the pipe in trench after the construction
of embankments.
3. If spongy, soft or other unstable material is met with at the location of pipe culvert, remove the
material to the required depth, width and length, and back fill with approved granular material
properly shaped and compacted to the required level.
4. Where rock or bouldery strata is met with, take down excavation to alleast 200 mm below the
bottom level of pipe, remove all loose material and fill the space with approved earth.
A 2 Loading and Unloading of Pipes
1. Make arrangements for lifting, loading and unloading of pipes from factory/yard to site, such
that no undue strain or damage occurs due to fall or impact.
2. For manual unloading from trucks, roll down pipes on a pair of skids hooked onto the trucks and
control movement with a rope passing round the pipes.
A 3 Laying of Pipes
1. Preload the areas to induce major portion of settlement before the pipe is installed.
2. Provide a bedding surface of firm foundation of uniform density, throughout the length of culvert
with specified bedding material depending on dia of pipe and height of fill above pipe.
3. Lower the pipes in bed either by tripod pulley arrangement or by manual labour using chain
pulley blocks in a manner to place them in proper position without damage.
4. When two or more pipes are laid adjacent to each other, place them separated by a distance equal
to half the dia of the pipe subject to a minimum space of 450 mm.
5. When pipes are laid in two layers, keep the centers of pipes such that when joined shall form
equilateral triangles.
6. Lay the pipes as specified in IS:783, for different conditions such as positive projecting condition,
trench condition etc.
7. Lay the pipes on the prepared foundation, commencing from outlet and proceed towards the
inlet. In case of pipes with bell mouth, keep the belled end facing the upstream. Keep the invert of
pipe minimum 150 mm below average bed level. However, if the invert level is more than 300
mm, a catch pit of size 1500 x 1000 mm upto ground level should be constructed.