Sewerage - Nagar Nigam Raipur

Project Management Consultancy Services for Sewerage, Storm, Surface Water Drains and Lake
Protection Works For Raipur City
Detailed Project Report - Sewerage
Chapter 5: Design Considerations
Class
Table-5.2: Different Beddings for Pipes in Trenches
Condition Load factor
A a Concrete cradle-plain concrete and lightly tamped backfill 2.2
A b Concrete cradle-plain concrete with carefully tamped
backfill
2.8
A c Concrete cradle-RCC with P-0.4% Up to 3.4
A d Arch type concrete
RCC with P-0.4%
RCC with P-1.0%
(P is the ratio of the area of steel to the area of concrete
at the crown)
B Shaped bottom or compacted granular bedding with
carefully compacted backfill
C Shaped bottom or compacted granular bedding with
lightly compacted backfill
Up to 3.4
Up to 4.8
D Flat bottom trench 1.1
The CPHEEO manual recommends B or C type of bedding with granular compacted bedding. All
the gravity sewers are designed as per CPHEEO requirement of structural design of buried pipes.
The detailed design sheets are placed in Volume-VIII.
5.5 Concrete Encasement
Concrete encasements will be used when it is necessary to prevent floatation, when crossing
streams, nalla or rivers and where crossing over utilities with less than 500 mm of clearance, or
in areas where the sewer has less than the required cover. The typical details of sewer encasing
are provided in Drawing No. STD-12.
5.6 Railway Crossings
The following criteria shall be followed when the sewers are required to cross rail tracks. The
schematic details of rail track crossing of sewers are presented in Drawing No. STD-18.
• Sewers shall cross tracks at an angle as close to 90 o as practical, but preferably never less
than 45 o .
• Sewer lines crossing under rail tracks shall be constructed adopting technology permitted by
the railway authorities.
• Sewer lines laid longitudinally along rail right-of-way shall be located away from tracks or
other important structures. The distance shall be minimum 5 m away from the edge of last
track. If not possible, the sewer shall be encased.
• When placed along rail track right-of-way, the top of the pipe shall have a minimum cover of
2 m.
5.7 Highway Crossing
The sewer pipe alignments under City maintained roads, which are designated by their
governing agencies, are to be crossed, shall meet the following requirements (more stringent
criteria may be required on a case specific basis):
Sewers shall cross the roads at an angle as close to 90 o as practical, but preferably never less
than 45 o . Sewers shall not be placed under roadway bridges where there is a likelihood of
restricting the required area of the bridge or where there is a possibility of endangering the
foundations. Sewer lines laid in a longitudinal direction on highway right-of-way shall be located
at sufficient distance from the edge of pavement to allow adequate working room and to
provide maximum safety to the motorist when the roadway is to remain open to traffic. The
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1.9
1.5