Specifications

NAIROBI OPERATIONAL HUB
UNOPS Building, UN Lane, Off UN Avenue Tel: [phone]
P.O Box 783,Village Market, 00621 E-mail: [e-mail]
Nairobi, Kenya Website: www.unops.org
UNOPS is ISO 9001 certified
A. Duct banks shall be either direct buried type or concrete encased type, as applicable
and required on site.
B. Heavy duty rigid PVC conduits shall be used for direct buried or concrete encased
underground duct systems. PVC conduits and fittings shall comply with the
requirements of Section 16130
C. PVC conduit shall be suitable for a temperature range of 4 °C to 90 °C. Conduits
within the duct bank shall be supported on plastic interlocking spacers, at intervals
of approximately 2.4 m. A 25 mm minimum separation, edge to edge, shall be
maintained, both horizontally and vertically, between the ducts.
D. All duct banks shall have a 75 mm concrete cover on the top, sides, and bottom of
the PVC ducts. Anchorage shall be used to hold the ducts in place while pouring the
concrete encasement.
E. Where the duct bank enters a building below ground level, the conduit shall
terminate in an appropriate fitting. An end bell shall be used on conduits entering
manholes.
F. After completion of the installation of cables in the duct bank, seal the ends of duct
banks using special caulking compound of a putty-like consistency. It shall be
workable with the hands at temperatures as low as 1.7
o
C, and shall not slump up to
a temperature of 149
o
C. It shall not be harden significantly when exposed to air.
G. A run of conduit shall not contain more than the equivalent of four quarter bends.
Bends in conduit shall be made without reducing the internal diameter of the
conduit. The inside radius of the conduit bends shall not be less than one metre.
H. Matching end bells and plugs, constructed of high impact plastic, shall be provided
through out the duct bank at the ends and in manholes.
I. Each length of conduit shall be provided with one standard coupling. Couplings
shall have a center step to ensure proper seating. Joints shall be made with the
solvent cement as recommended by the conduit manufacturer.
J. Concrete encasement shall be class C20 concrete with 13 mm maximum size
aggregate for all duct banks. For warning purposes, a red dye shall be towelled into
the top surface after pouring the concrete.