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

Chapter 5 Water Infrastructure
are required by other entities (e.g. railroads) where SPU utilities cross over or under them.
Casings can be installed via open cut if there are no obstacles.
Casing materials must follow Standard Specifications 9-30.2 (14) and 9-30.2(15).
A. Jacked Casings
Casings installed under the railroad are often jacked into place. When designing jacked
casings, adequate space is required for the casing and pipe jacking pit. Jacking pit size
can vary depending on the lengths of casing or pipe. Restrained joint pipe must be used
through the casing and beyond to a logical location to terminate the restrained joint
pipe. Keep in mind that the cased length of pipe offers no thrust resistance via skin
friction as does a buried pipe. Access must be provided for the pipe to be cut and
connected to a new pipe. SPU preference is to have the jacking pit located on each side
of the casing.
Note:
Jacking casing is dependent on pipe size. The larger the pipe size, the larger the
jacking pit is. Keep the casing as far as practical from the other utilities to allow future
access for pipe removal.
B. Other Utility Crossings
The design engineer must determine where casings are needed at locations where an SPU
transmission main is crossing either over or under other utilities. For separation requirements
between water mains and other utilities, see Standard Plans 286A and 286B. All pipes in casings
must be restrained joint. See Standard Specifications 7-11 3(6)D and 7-11.3(7)C-D2.
C. Railroad Crossings
Where water mains cross under a rail system (e.g. street car, light or heavy rail, or other
as determined by SPU), the main must be placed inside a casing. The casing must extend
such a distance from the tracks that maintenance can be performed from the side
without affecting the rail. For cathodic protection for pipes crossing a rail line, see DSG
Chapter 6, Cathodic Protection, Test Procedure (TP) 31 – Light Rail and Street Car
Cooperative Interference Testing.
i
Heavy Rail
When crossing beneath heavy rail, a casing must extend from ROW line to ROW
line unless the main is more than 25 feet from the track centerline. If the
railroad agrees, the casing must extend a minimum of 25 feet from the track
centerline. See the American Railway Engineering and Maintenance-of-Way
Association (AREMA) Design Guideline before designing a heavy rail crossing.
Pipelines parallel to heavy rail must be encased if they are 40 feet or less from
the track centerline.
ii
Light Rail
Light rail does not impose the extreme loading on pipelines that heavy rail does.
However, light rail imparts some loading and causes significant pipeline access issues
and stray current corrosion concerns.
SPU Design Standards and Guidelines
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