Subterranean Guided Boring in Toronto
In early 2020, Earth Boring Co. Ltd. was approached by C&M McNally Tunnel Constructors as part of Enwave Energy’s Low-Carbon District Energy System East expansion project in Toronto.
C&M McNally is the tunnel contractor and general contractor on the Enwave project, which delivers sustainable, carbon-friendly, energy services to Toronto’s East Bayfront community. In all, C&M McNally mined a 1.2 km extension of a previously constructed, 3.55-m diameter tunnel, bringing the overall district energy tunnel to 1.96 km long. Along the 1.2-km of new tunnel, there were three building connections and a fourth connection in an existing tunnel that C&M McNally previously constructed for Enwave. Each of the four connections provided its own unique challenges. The connection at 100 Queens Quay East proved to be the most difficult.
C&M McNally looked to Earth Boring Co. to install four, 18-in. diameter inclined tunnels to connect heating and cooling services to the building, which includes 75,000 sq ft of retail space and 600,000 sq ft of office space, including 225,000 sq ft for the new Liquor Control Board of Ontario (LCBO) headquarters.
“We had our own space delineated by the [building’s] general contractor under our own notice of project within a building that was still under construction. For everything other than man access we had to arrange with the general contractor to transport all equipment/materials and spoils in and out of the basement to the bottom of the ramp,” says Greg McNally, project manager at C&M McNally. “For the Earth Boring portion, the garage and the mechanical room were already constructed. They were going into, for all intents and purposes, a finished building and breaking out an existing foundation wall and drilling down into the [main] tunnel.”
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Because construction on the building was already under way, the crew had to complete the bores in the utility room of the building spaced at 1.1-m intervals, with entry points at approximately 1.1 m off the floor and an incline of 25.58 per cent.
The bores were each approximately 28 m long and had strict line and grade requirements to ensure that appropriate connections could be made at the Enwave utility tunnel at the receiving end. This bore was also atypical as the Enwave utility tunnel was being drilled at the same time as these shots, so no receiving shaft was available. The bores would be completed through partially fractured and highly saturated shale.
In addition to the complex installation requirements, the jobsite posed several other logistical challenges:
- The drilling location was at Basement Level 5 (21 m below ground) with the nearest access point being an underground parking garage in Basement Level 4.
- The utility room itself was only 9 m wide, irregular in shape, with a concrete column 0.9 m off line of the east most bore.
A floor that sloped by 1 per cent.
- A 1.2- by 1.2-m sump pit in the middle of the room.
As the building was still under construction it was shared by numerous contractors. The only staging area available for the tools and equipment was outside the building itself, more than 34 m away from the drilling point.
Staging was the first hurdle, but well-grounded planning helped facilitate a safe and expedited mobilization down the stairs to the mechanical room. A local millwright was enlisted to disassemble the equipment, create a suitable lifting jig to navigate the equipment down the stairs and re-assemble in the basement. The use of portable gantry cranes supported reassembly and the ongoing bore effort.
“The mechanical room was a floor below the rest of the basement, and all the drilling equipment including the stand had to be hoisted down the staircase. For the drill rig and stand we approached Thompson-Miller Specialty Rigging,” says McNally. “In order for the Akkerman machine to fit, Thompson-Miller set up a custom gantry crane, they also had to disassemble the GBM then reassemble it in the mechanical room.”
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Completing the Bores
To complete the 18-in. connections, Earth Boring Co. proposed the use of its Akkerman 240A Guided Boring Machine (GBM) on a specially designed stand supported by an Akkerman P100E Power Pack and a combination of the pilot tube system and a guided expanding auger cutting head.
The stand was designed in-house by the Earth Boring Co. engineering team to angle and place the machine to meet the design line and grade requirements all while being light and mobile enough to move around the utility room and strong enough to sustain the applied pushing and rotational forces from the machine. The frame included a set of lagging points around the base of the frame which allowed for the installation of 6 ¾-in. anchor bolts to keep the frame grounded. This was later increased to 24 anchor points following the discovery of numerous utilities, including a 600 V power line, 4 in. below the concrete floor slab.
The increased number of anchor points allowed the team to select anchor locations as needed to avoid utilities on each of the individual shots, while ensuring the frame remain adequately fixed.
The frame also included two 4-in. cube steel beams with pivot heads as back braces. These braces connected directly from the back of the machine to the back wall of the room and were lagged into the wall to provide a “back plate” that the machine could push on. Power and a bentonite slurry mix was fed to the machine from a staging area on the surface more than 34 m away.
Each bore was completed by piloting the design length, pulling back to the sending point and then following through the pilot hole with a custom built expanding auger cutting head with a special guidance fitting and an 18 in. steel casing sleeve. Spoils and ground water from the face were pulled back to the sending side using a string of augers, from where a hydro-vac truck sucked the material the rest of the way to the surface.
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Overall, the works seem straight forward, but not without some added challenge. The GBM had not been adjusted to leverage in this sort of fashion, and piloting and enlarging the bore hole was a unique challenge, limestone stringers in the shale matrix regularly ‘tangled’ up productionand advancement rates were severely impacted. In one instance the reaming assembly was lost downhole, fortunately within the main tunnel influence that supported a retrieval from the receiving end of the works.
“During Earth Boring’s work, we continued to support their operation and remove the spoils,” McNally says. “Once Earth Boring had completed the four bores, we installed the piping and then re-instated the rebar with waterproofing and finally shotcreted the four openings closed.”
As if the boring portion was not challenging enough, the project’s complexities were compounded by the early days of the COVID-19 pandemic and a provincial-wide shutdown of non-essential construction activities.
“Earth Boring worked hard to ensure the work was considered under the ‘essential works’ mandate of the Ontario government. Beyond outreach to acquire written validation of this preferment, was ensuring that the onsite forces were working within Earth Boring Company’s own policies and procedures to ensure the workers had a safe environment to work,” says John Currey, vice president of operations at EarthBoring Co. “We applied stringent polices around self identification of wellness, onsite hand wash stations, N95 face coverings and strict protocol on the use of the N95 PPE when working within 3 m of co-workers.”
With the more stringent health and safety measures in place, Earth Boring Co. used the Site Docs application to document the workers adherence to the program. Site Docs allowed for screening questions and responses to be posed to the workers at the start of each shift. Additionally, the company used the ExakTime time recording app to leverage pre-screening health and wellness questions as the workers signed into each shift.
“The use of the ExakTime app also provided critical contact tracing abilities when an adjacent work crew had reported a worker may have been in contact with a COVID-19 positive person. By use of the ExakTime tool, we were able to identify that our workforce had not been in the same area as the other worker,” Currey says. “The peace of mind this left our workforce was immeasurable. The added benefit of being able to keep the project running was extremely valuable overall.”
Like Earth Boring Co., C&M McNally had to — and continues to — deal with the COVID-19 pandemic and more stringent safety measures. While its own tie-ins were complete in advance of the pandemic, its mining operations were still ongoing.
“We worked with Earth Boring [on planning their safety measures] but they were on their own site with a couple of our guys assisting them. There wasn’t much more than an additional washing station and PPE as per the government’s recommendations at the time,” McNally says. “For our mining operation, which happened during the first shutdown, we were not shut down because we were deemed to be an essential service. We implemented offset shift times, so crews could not intermingle. One crew came in, did their [10-hour shift] work, and then left. We had 30 to 60 minutes of dead space between the shifts.”
With the mining complete C&M McNally is now working on laying in the hot- and cold-water pipes and finishing concrete work on tunnel. There is no longer a break between the two shifts as they are working on different sections of the drive and each group has their own washing stations and restroom facilities.
Expected completion of the overall project is fall 2021.
This story was compiled by the Trenchless Technology Canada staff with information provided by Earth Boring Co. Ltd. and C&M McNally Tunnel Constructors.