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

The area is on a steep slope and particularly if the water main is to be in an area
determined to be a slide area.
If the site is congested with underground utilities or other facilities such that
concrete thrust blocks are unfeasible.
To provide flexibility in shutdown areas and avoid using temporary thrust
restraints.
In areas where excavations, soil settlement or subsidence is anticipated,
restrained joint pipe should be considered.
In pipelines critical to the functioning of the water supply system after a major
seismic event.
i
ii
Wedged Restraints
Other examples of flexible restrained joints are a wedge restraint gland type device or a
restrained gasket type of pipe. Wedge restraint glands must follow Standard
Specification 9-30.5(5)B. Wedge restraint glands are typically used on mechanical joint
pipe and fittings and grip the pipe, which forces a lug with teeth to imbed into the pipe.
Most wedge restraint systems remain flexible after installation.
Gasket Restraint
The restraint gaskets are readily available and can be installed on field-cut push-on joint
pipe. The restraining gaskets have stainless steel teeth imbedded in them that grip the
pipe for restraint. The restraint gaskets are only pseudo-flexible restrained joints. Once
assembled, they offer little or no deflection capability. They also require special tools to
disassemble.
Note: SPU has used the restraint gaskets on occasion, but found they do not save costs.
The AWWA M41 Manual or DIPRA computer program can be used to calculate ductile
iron pipe restraint requirements.
Restrained joint pressure ratings for each type and pipe size must be verified with the
manufacturer. The length of pipe in casings on any run of ductile iron pipe does not
count towards its overall restraint length, unless the casings are filled with grout after
the pipe is installed. When using restrained joint pipe, all pipe in each individual system
must be restrained joint. In addition to pipe joint restraint, concrete thrust blocks must
be provided unless site-specific conditions do not allow.
Note: Field cutting and modifying a factory restrained joint pipe is difficult and time
consuming. The pipe must be ordered specific to the project site. Contractors must
submit and receive approval of a 3-D lay plan before ordering pipe.
iii Grooved Restraint
Grooved restraint couplings can be used to restrain ductile iron and steel pipe. These
couplings are uncommon in the SPU system but can be found on some blow-off
facilities. Grooved restraint couplings are generally not used in buried service.
The standard grooved restraint coupling engages a groove that is cut on the exterior of
the full circumference of the pipe. Thicker pipe must be used for these couplings.
5-28 SPU Design Standards and Guidelines