North American Special - Trenchless International

During the above process WP was
planning for the Pine Creek HDD.
Success of the HDD was contingent on
obtaining adequate subsurface geotechnical
information to assist in engineering
the crossing; the geotechnical investigation
was completed in January 2007.
Construction of the Pine Creek Loop was
carried out successfully, with the Pine
Creek HDD slated for July 2007.
Due to the protected status of the La
Biche River Wildland Park, no additional
ROW was being granted within the park.
WP attempted to design an HDD crossing
with this restriction in mind but could
not achieve the desired results based on
the following:
• The existing AOSPL ROW configuration
was designed to accommodate
the previously installed trenched
crossing. There were changes in horizontal
direction both upstream and
downstream of the crossing.
• A number of adjacent pipelines within
the area had to be crossed along the
HDD path.
• The minimum design radius of curvature,
required clearance from the
bottom of Pine Creek and the required
entry and exit angles.
To ensure Pembina would be successful
in obtaining the required approvals,
WP chose the final alignment to utilise
only existing cleared areas for the
Above: Construction on hot lines with mats.
Below: Direct Horizontal Rig AA 440,000 lb.
necessary ROW required by the HDD
alignment. The final design involved
entry and exit angles of 10 degrees.
Entry angles are typically steeper in
order to minimise the potential for fluid
releases to surface near entry and exit
but 10 degrees was essential to limit
the overall length of the HDD. The depth
under the creek was set at the required
minimum of 15 metres as noted in the
geotechnical report. The alignment and
length chosen had under crossings of
the Suncor and Shaw cable utilities. As
access on the north side of the crossing
within the Park was limited, the drill entry
point was established on the south side,
even though the elevation was slightly
higher than the north side. The total
design length was about 440 metres. As
a result of the alignment of the drill and
the adjacent hot lines, extensive rig mats
were required to allow work to be carried
out over the top of these lines as well as
most other aspects of the work.
Ledcor Pipelines was awarded the
mainline contract for the Horizon Pipeline
Project. Ledcor subsequently awarded
the HDD subcontract to Direct Horizontal
of Stoney Plain Alberta. Direct completed
the NPS 24 La Biche River crossing with
an American Auger DD440 and moved
the same drill rig to the south side of Pine
Creek in July 2007. The selected drill rig
(pictured) can be set up to enter at a
minimum of 12 degrees, steeper than the
designed entry of 10 degrees. Due to this
change in the vertical alignment and the
deepening of the bore profile as a result
of steering difficulties, the total length of
the drill ended up at 494.3 metres, an
increase in length of about 12 percent.
Problems with fluid releases close to
the rig were encountered as a result of
the soft ground and the shallow depth
due to the shallow entry angle. Ultimately
the contractor chose to put in 40 metres
of 42 inch casing and then installed 70
metres of 12 inch casing to minimise the
fluid releases to surface. The 12 inch
casing was utilised during the pilot hole
drilling to try to ensure that the pilot hole
was not lost as a result of the tripping in
and out of the pilot hole in the soft clay
formation.
In addition, the contractor requested
changes to the drill path to allow for a
deeper drill path to minimise fluid releases.
The minimum radius for the drill was set at
600 metres at any point along the drill.
Due to the soft nature of the clay, steering
was somewhat difficult, requiring frequent
adjustments. Ultimately the contractor was
successful in completing the pilot hole
and the first ream.
At this point the engineer was provided
the as-built drill profile survey data for
review. Engineering Technology Inc of
Calgary (Entec) was contracted to review
the survey data and provide information
regarding the drilled radius of the crossing.
Entec used the industry accepted
‘dogleg’ method to calculate the minimum
radius along the drill path. The smallest
radius found was 270 metres and another
16 points where the radius was below the
Above: View of product pipe.
Below: Successful pipe pull.
minimum recommended radius of 600
metres.
The 270 metre radius was calculated
to be close to failure under installation
stresses and beyond failure under operating
stresses. Due to the large discrepancy
between the pilot hole minimum radius of
270 metre and the recommended minimum
radius of 600 metres a more refined
analysis of the crossing would be required
to accurately determine if the current pilot
hole drill path was in fact acceptable.
There are a number of methods available
for calculating the combined stress
within an HDD drill path. The Tresca, Von
Mises and limit states approaches are
all recognised within the CSA Z662 and
offer varying degrees of conservatism.
Regardless of the method chosen stress
is analysed for a pipeline within the HDD
path for the maximum operational conditions.
The presence of applied loads in more
than one direction results in a much more
complex state of stress than for applied
loads in only one direction (uniaxial). The
predominant stresses in pipelines are typically
biaxial, with internal pressure acting
in the circumferential (hoop) direction and
thermal loads and beam bending acting
in the longitudinal direction. The yielding
of the steel under these conditions is
considerably more complex, and there
are two widely accepted approaches for
determining the combination of stress in
various directions that result in yielding
of ductile material (such as steel); the two
approaches are the Tresca theory and the
von Mises theory (Please refer to the conference
paper for further information).
The combined stress as per CSA Z662
April 2009 - Trenchless International
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April 2009 - Trenchless International
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