August 25, 2016As the Greater Toronto Area (GTA) grows, the demand for energy also increases. In order to meet this demand, Enbridge Gas Distribution commissioned the GTA Project to upgrade the existing natural gas distribution system that currently delivers natural gas to Toronto and the surrounding areas.
Mears Canada Corp. (Mears) was awarded the horizontal directional drilling (HDD) and Direct Pipe crossings on the 42-in. pipeline section of the project. The entire GTA project traverses six municipalities and three regions within the GTA. Numerous approvals from various agencies were required in order to construct the project. A total of 235 permits, for roughly 50 km of pipe, were required to be obtained from the various permitting agencies impacted by the project.
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Mears performed a total of seven crossings. Six of the crossings were installed via HDD and one was a Direct Pipe crossing. Mears used four rigs for the project: two 140,000 lbs, a 1.3 million lbs and a 1.1 million lbs. Mears brought in its strategic alliance partner, Innovative Pipeline Crossings (IPC), for the Direct Pipe installation. The HDD installations — of 1,266 ft (386 m), 1,670 ft (509 m), 1,735 ft (529 m), 1,765 ft (538 m), 3,398-ft (1,036 m), and 3,897 ft (1,188 m) — were located at Finch Avenue/Claireville Reservoir, Highway 401, Mavis Road, Bramalea Road, Highway 410, and Mississauga Road/Levis Creek and the Direct Pipe was located at Credit River/Orangeville Railway.
Record-Breaking Cold Temperatures
Mears mobilized in January 2015 and began drilling at the Finch Avenue/Claireville Reservoir crossing located in the west end of Toronto. This was the longest of all the crossings and the most challenging. At a length of 1,185 m (3,885-ft), the drilling phase of the crossing occurred during one of the coldest winters Toronto had experienced in 50 years, with temperatures as low as -25 C (-13 F), with wind chills that neared -45 C (-49 F). The Mears’ crews ran mobile boilers 24/7 to keep the equipment from freezing.
One major challenge of this particular crossing was the variable geology of differing rock, clays and silts. Variations in the hardness of the subsurface materials contributed to a misalignment within the bore hole close to the exit point after it had been pre-reamed. Soon after the start of the pullback operation, it became evident that the pull-head (attached to the leading end of the pipeline) was dropping below and unable to follow the designated path. To assess the situation, the pipeline was pulled back out and a survey probe was inserted into the bore hole. The results confirmed that a short section of the borehole was undermined. This had caused the product pipe to drive into the ground instead of following the intended bore path.
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To solve this problem, Mears director of operations Steve Meaders and Mears equipment manager Karl Quackenbush designed a 60-ft transition pull-head that gradually increased from 24- to a 42-in. pull-head. The idea behind the longer transition pull-head was that the smaller diameter section would follow the bore path and lead the product pipe to do the same. The modified pull-head guided the product pipe through the bore hole for a successful completion of the first crossing.
The Credit River/Orangeville Railway crossing was a particularly challenging crossing due to the various sensitivities in the area. It involved crossing archeological sites, the river (popular for salmon fishing), a rail line, and an environmentally sensitive wetland area.
There was artesian water pressure in the bedrock making ground conditions potentially unstable east of the river. On the west side, boulders and bedrock were present at a relatively shallow elevation. Because of these conditions, although the original intent was for the crossing to be made using HDD, Direct Pipe was selected as the most suitable method of construction. This allowed a shallower and shorter crossing.
The pipe fabrication area was in a temporary work space south of the pipeline’s permanent easement. The gravel road was not exactly in line with the alignment of the pipeline. The offset of the gravel road required incorporation of a slight curve in the pipe fabrication’s alignment. Difficulty in handling the curve in the pipe was compounded by the slope of the ground as it ran down toward the river and the stiffness of the 25.4-mm (1-in.) wall thickness of the pipe. Multiple cranes were needed to elevate and support the pipeline as it traversed the vertical and horizontal curves. The cranes and side booms did not allow for any access from the west along the work space and easement except for access by foot. The road access to the launch pit was cut off. A new smaller access for light vehicles and emergency services was built just south of the launch pit utilizing existing walking trails in the area.
Once the pipeline was pre-fabricated, the microtunneling machine’s power and control lines and the drilling fluid feed and return lines were inserted inside the full length pipe. The pipeline was brought into position at the launch pit; the microtunneling machine was attached to the front of the pipeline. Then, using the 750-ton pipe thruster, the crossing was made in a single pass. The operation took 11 days to complete and less than 100 tons of thrust, with entry and exit angles of 6 degrees. The crossing was completed on April 16, 2015.
Highway and Road Crossings
The Highway 410, Highway 401, Mavis Road and Bramalea Road crossings were all approximately 500 m (1,640 ft) long. The Highway 410, Mavis Road and Mississauga Road/Levis Creek crossings required installing two separate sections of product pipe during pullback due to the lack of space. In most HDD crossings, the pipe is strung in one continuous section. But in the case of these crossings, one section of pipe had to be pulled into the bore hole until space allowed for the second section of pipe to be welded to the trailing end of the first, and then the second half of the pullback operation could be completed. Making these mid-pullback tie-ins can increase the operation’s risk since, in the time it takes to make the intermediate tie-ins, the condition of the borehole can deteriorate and difficulties can be experienced in restarting the pullback after the tie-in has been completed. The tie-ins on these crossings took roughly 10 hours each (to reposition the pipe string, complete the welding and complete the coatings). In each case, the condition of the borehole was such that the pullback was able to re-commence without any issues.
The Mississauga Road/Levis Creek crossing was the last installation of the project and the second longest crossing at 1,033 m (3,390 ft). This crossing was drilled with an intersecting pilot hole. A directional drilling rig was placed at the exit and another at the entry side of the crossing. By drilling toward each other and meeting, a continuous single borehole was created. Due to the high probability of cobbles within the first 90 m of the crossing, a 60-in. casing was installed on the entry side for the Mississauga project site.
This large project required Mears to manage six drilling rig spreads (dual rigs were used for reaming), the IPC Direct Pipe spread and 14 crews running the 24-hour operations. All seven crossings were successfully completed allowing final demobilization of equipment and crew in October.