PIPE CULVERT
By
CH. VENKATARAMAIAH
(1) A pipe culvert is normally proposed where a canal with a
discharge of 1 cumec to 1.5 cumec crosses the village/
Z. P / R & B roads. In case the number of rows of pipes
exceeds ‘2’ the pipe culvert may not be economical. In
such cases the slab culvert may be economical. The
culvert shall be with full formation width of road as per
IRC recommendation.
(2) Pipe
(i) Maximum & Minimum diametre of pipe:
The maximum diameter of pipe should be 1200 mm and
minimum diameter should be 750 mm. It shall be
designed to function as partially flowing with the
velocity not more than 2 times the normal canal
velocity.
(ii) Class of pipe: NP3 class (reinforced concrete,
medium – duty, non pressure pipe), conforming to
I.S 458 – 2003 / 1988.
(iii) Minimum Earth cushion: Minimum earth cushion
over the pipes shall be 600 mm.
(3) Bedding:
Irrespective of load coming on the pipe, they shall be
bedded in a cradle constructed of concrete having mix
not leaner then M 15 grade. Thickness of concrete
below the pipe should be ¼ th of internal diameter of
pipe and on the sides the concrete should extend to ¼ th
of external dia. Figure A
Figure A
Where bed rock or boulders strata is met with at the pipe
invert level, the excavation shall be taken down at least 200
mm below the bottom of pipe. The bed shall be cleared and
the space shall be filled with well graded sand or granular
material free from stone or fragmented material, shaped to
the requirement and thoroughly compacted to provide
adequate support for the pipe Figure B.
Figure B
(4) Trench:
As per Para IS 783 – 1985 page 373 of the specifications
for road bridge work, trench shall be of sufficient width
to provide a free working space on either side of the
pipe. The working space shall be preferably not less than
150 mm and shall not be more than one third of the dia
of pipe.
The minimum clearance between the pipes shall be at
least half the diameter of the pipe subject to a minimum
of 450 mm. Trench shall be kept free from water until the
pipes are installed and the joints have hardened Figure C.
Figure C
(5) Jointing:
The pipes shall be joined by the collar joints. Collars
shall be of R.C.C, 150 mm or 200 mm wide having same
strength as the pipes to be joined. Caulking space shall
be between 13 to 20 mm according to diameter.
Caulking material shall be cement and sand in the ratio
of 1:2.
(6) Vent way:
Area of pipe = Q/ 2 x Vn
where Q = discharge of canal, Vn = normal velocity in
the canal.
Select the pipe diameter, more than canal F.S.D so that
there is partial flow in the pipe. If it requires more than
two pipes, go for slab culvert. The partial flowing pipes
area is calculated with the help of table given below.
a = Ca d2
where a = area of partial flowing pipe
Ca = value as per table
d = dia of pipe , D = depth of water
Value of Ca
D/d
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.0
0.0000 0.0013 0.0037 0.0069 0.0105 0.0147 0.0192 0.0242 0.0294 0.0350
0.1
0.0409 0.0470 0.0534 0.0600 0.0668 0.0739 0.0811 0.0885 0.0961 0.1039
0.2
0.1118 0.1199 0.1281 0.1365 0.1449 0.1535 0.1623 0.1711 0.1800 0.1890
0.3
0.1982 0.2074 0.2167 0.2260 0.2355 0.2450 0.2546 0.2642 0.2739 0.2836
0.4
0.2934 0.3032 0.3130 0.3229 0.3328 0.3428 0.3527 0.3627 0.3727 0.3827
0.5
0.3930 0.4030 0.4130 0.4230 0.4330 0.4430 0.4530 0.4620 0.4720 0.4820
0.6
0.4920 0.5020 0.5120 0.5210 0.5310 0.5400 0.5500 0.5590 0.5690 0.5780
0.7
0.5870 0.5960 0.6050 0.6140 0.6230 0.6320 0.6400 0.6490 0.6570 0.6660
0.8
0.6740 0.6810 0.6890 0.6970 0.7040 0.7120 0.7190 0.7250 0.7320 0.7380
0.9
0.7450 0.7500 0.7560 0.7610 0.7660 0.7750 0.7750 0.7790 0.7820 0.7840
(7) The road level should be at the Road level / G.L/ TBL
whichever is higher. 300 mm thick P.C.C slab shall be
provided over the pipes with 75 mm wearing coat in M 20
with 6 Ф at 200 c/c both ways at top & bottom.
THANK YOU