2013 Water System Plan, Volume II - Seattle City Clerk's Office - City ...

pressure and friction on the bottom surface of the block. To keep the pipe from sliding
within the collar, the concrete needs to interface with the pipe. The wedge restraints on
ductile iron pipe should be wrapped in polyethylene so the concrete does not seep into
the wedges of the wedge restraint gland and stop it from working.
i
ii
Steel Pipe
If using concrete collars on a steel pipe, a factory integrated thrust ring must be welded
around a pipe section, then embed in concrete.
Ductile Iron Pipe
If using concrete collars on ductile iron pipe, a factory ring must be installed on a pipe
section. An alternative is to install two wedge style restraints face-to-face to act as a
thrust ring.
iii Poor Soil Conditions
Design should consider the potential settlement impact the concrete thrust collar could
have on the pipe.
iv Pipe Anchors/Tie Backs
Pipe anchors consist of a large mass of concrete usually on one side of a pipeline. The
concrete is attached to the pipeline by steel rods. Anchors act like vertical thrust blocks
(except in a horizontal plane) to restrain the pipe at a bend. Typically, pipe anchors are
only installed for temporary service because the rods can corrode.
C. Rigid Restrained Joints
Flanges, welded joints, and threaded couplings are types of rigid restrained joints.
Flanges can be used on both ductile iron and steel pipes. SPU does not use threaded
couplings in water mains.
i
ii
Flanges
SPU does not recommend burying flanges in soil. Flanged fittings are used where joint
flexibility is not needed and are typically found in vaults associated with valves or other
appurtenances. Flanged pipe must be installed perfectly to fit up and offers no
flexibility. A dismantling joint must be used to allow disassembly and repairs. Flanged
valves are usually used in the installation of a large run of flexible restrained joint pipe.
Each flanged valve will have a short flange by flexible restrained joint adapter on each
side of it.
Manufacturers can weld a flange to the steel pipe. See AWWA Manual M-11 for the
class of flange rating. Consult with the manufacturer to ensure the flanged connection
can be provided. An electrical isolation kit may be necessary if joining the steel pipeline
to a ductile iron appurtenance. Steel and ductile iron are dissimilar materials that can
corrode.
Welded Joints
Steel pipe can be assembled with welded joints, making the pipeline fully restrained.
Field-welded joints provide restraint against the unbalanced hydrostatic and
hydrodynamic forces acting on the pipe. There are several styles of welded joints. The
5-26 SPU Design Standards and Guidelines