Plastic water main used in restricted space in Ottawa
By Brian C. Harris, P.Eng.
St.Patrick Street Rehabilitation in the City of Ottawa.
Trenchless pipeline installation
projects can be especially
challenging when undertaken
in urban surroundings where
space is limited and traffic must be
managed. In addition, the proximity of
other underground services, as well as
the need to ensure the safety of both
the workers and the public, requires
careful planning and design in order
for the project to run smoothly.
Stantec Consulting (Ottawa
Office) recently completed a
project with the City of Ottawa
that included the installation of
sewers and water mains that
were 95% within the intersections
of four major roads:
Sussex Drive, St. Patrick
Street, Murray Drive and
MacKenzie Avenue. These
streets are located in a major
tourist area near the National
Gallery of Canada, Canada’s
Peacekeeping Memorial and
the U.S. Embassy. The heavy
traffic through the area
required that disruption be
kept to a minimum and considerable
traffic management and
construction staging be undertaken.
While the roadbed consisted
of granular material from
1.1 to 1.4 metres in depth, the
depth of the frost line required
that the water pipe be installed
at least 3 metres below grade.
This meant it was being
installed in very strong limestone
bedrock, with fractures
to various depths at some locations.
Open cut excavation
using hoe-ram or blasting techniques
was quickly ruled out due to the constraints
posed by the site. In addition,
the rock hardness and depth of rock
were factors in determining to place
the pipe via horizontal rock boring in
order to minimize disruptions.
The entrance (tunneling) pit was
located adjacent to the Sussex Drive
median in the west bound St. Patrick
street traffic lanes. Placement of the pit
at this location provided for shorter
drilling distances, and, therefore,
greater accuracy. Pit location also provided
for the security of the drillers to
ensure a successful operation.
Traffic constraints and the location
of the entrance pit eliminated the
option of butt-fusing long lengths of
HDPE pipe above ground and then
pulling it into the entrance pit. Long
lengths would have disrupted traffic
for the entire duration of the trenchless
installation, as the pipe must be completely
fused before installation
begins. This would have meant that a
75 metre length of 300 mm diameter
pipe would be stretched across a major
downtown intersection for hours.
TerraBrute offered a solution to this
issue as 6 metre lengths could fit
inside the entrance pit, eliminating
need to string pipe across the intersection.
Each segment of pipe could be
assembled as the pipe was pushed in.
TerraBrute’s standard bell and spigot
joint uses the same gasket and bell
design that city staff and contractors
are familiar with, and even has removable
gaskets in case oil resistant
(nitrile) gaskets must be substituted.
The unique locking mechanism on the
joint allows the pipe to be pushed or
pulled into place, and can withstand
the highest pulling forces. This property
was important in this case as it provided
flexibility, enabling
the pipe to be pulled through
the tunnel as pushing proved
to be impractical.
The pipe was pushed into
place with no problems and
the pipe was grouted into
place once it was located
within the rock bore.
The TerraBrute joint was
designed by Dr. Erez
Allouche, a noted expert in
the field of trenchless technologies
at the University of
Western Ontario. While his
main interest was to modify
the joint on standard C900
pipe to allow it to be used for
directional drilling, he also
sought to make the product
as versatile as possible by
allowing the locking mechanism
to accommodate thermal
expansion and contraction
(essential for bridge
crossings), as well as both
pushing and pulling forces.
In addition, the mechanism
he developed will withstand
over 120,000 lbs of straight
pull force for 300 mm pipe –
the strongest thermoplastic
pipe ever developed for
these applications.
Ishwar Bhatia and Fern Marcuccio
of the City of Ottawa, John Kubiseski,
Marathon Drilling, and Surrinder
Aggarawal, Trow Consulting, assisted
in this complicated project, completed
with a minimum of disruption in one
of the busiest areas of the City.
Brian C. Harris, P.Eng., is an
Associate with Stantec Consulting
Ltd.
Tel: 613.724.4374
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