The Eglinton Crosstown LRT is implemented by Metrolinx (an Agency of the Government of Ontario), and represents the first in a series of coordinated transit projects integrated across the Greater Toronto and Hamilton Area in southern Ontario. At CAD 5.3bn (2010 dollars [USD 3.97bn]) it is the largest transit expansion ever undertaken in Ontario’s history and the first LRT constructed in Toronto. The new 19km-long line will stretch along the busy Eglinton Avenue in dedicated right-of-way transit lanes from Mount Dennis at Weston Road to the existing Kennedy Station, and includes a 10km underground section from Black Creek Drive in the west to Brentcliffe Road in the east and up to 25 stations and stops along the corridor. The Crosstown represents a vital addition to transit in Canada’s largest city connecting more than 50 bus routes, three subway stations and numerous GO Transit (commuter rail) lines.

The 10km underground portion of the line is comprised of twin 5.75m ID tunnels divided into two tunnelling contract packages, the West Tunnels and the East Tunnels, that include emergency exit buildings and cross passages. Emergency exit buildings serve as tunnel connections for egress to surface used in the event of an emergency. The West Tunnels contract stretches 6.2km from Black Creek Drive to Yonge Street, with construction awarded to Crosstown Transit Constructors, a joint venture of Obayashi, Kenny Construction, Kenaidan, and Technicore Underground for CAD 320M (USD 239.8M) in September 2012. The East Tunnels contract stretches 3.3km from Laird Drive to Yonge Street, with construction awarded to ADJV, a joint venture of Aecon and Dragados for CAD 177M (USD 132.66M) in November 2013. A total of four owner-procured EPBMs, two for each contract, and a single-pass segmental precast concrete tunnel lining (PCTL) were used to complete the 20km of tunnels for the Crosstown. Hatch Corporation (formerly Hatch Mott MacDonald) along with Parsons Corporation (formerly Delcan) and WSP Global Inc. (formerly MMM) formed the joint venture 4Transit and was selected by the owner, Metrolinx, to provide construction management services for the tunnel contracts.

TBMs and PCTL

As a means of advancing the project schedule, the TBMs and PCTL were procured under separate advanced contracts. Hatch designed the tunnel lining, developed the specifications for the TBMs and provided technical assistance during the TBMs and PCTL procurement process.

The four 6.5m OD mixed-face EPB TBMs were manufactured by Caterpillar Tunneling Canada Corporation (CAT) in Toronto. The cutterhead was outfitted to accommodate rippers and/or disc cutting tools. The TBMs also included tail shield annulus grouting with a two component grouting system, three rows of tail shield brushes to prevent ground and grout ingress, and an inflatable emergency seal in the event of a failure of the tail shield brushes. The TBMs were approximately 11m in length with 80m of trailing gear. Decast Ltd. (formerly Munro Ltd.) manufactured 14,750 PCTL rings, north of Toronto. Each 5.75m OD universal PCTL ring was 250mm thick, 1.5m wide and made up of six segments. Among other features, the segments included: steel reinforcement cages, EPDM-rubber gaskets, radio-frequency identification tags and grout injection ports. The design also incorporated dowels and guide rods that assisted the contractor in effectively aligning segments contributing to a high-quality ring build.

Tunnel design

Hatch performed preliminary and detailed design for the design-bid-build twin tunnel contracts. The design required careful consideration to more than 1,400 building encroachments on private properties, utility treatment and traffic management in the narrow 20m road right-of-way. The design also included station headwalls that were installed in advance of the TBM tunnelling and mined through during the tunnel drives. In some locations, headwalls were prescribed and installed by jet grouting below the existing utilities to minimise the need for relocations. Hatch developed an innovative approach to settlement prediction and impact assessment using the in-house program Settlement Impact Database (SID). SID was used to estimate impacts on the almost 1,500 structures within the tunnelling zone of influence and was efficiently modified and re-evaluated based upon changes during the design and construction phases.

A Closer look at the east tunnels contract

The East Tunnels Contract included the main TBM bored drives consisting of Tunnel Drive 5 (future westbound LRT service) and Drive 6 (future eastbound LRT service). In addition to the 3.3km twin LRT tunnels, the East Tunnels included two emergency exit buildings, two cross-passages, construction of a launch shaft, extraction shaft and headwalls at each end of the future stations located at Laird Street, Bayview Avenue and Mount Pleasant Road. The East Tunnels began tunnelling in September 2015 and completed both drives in August 2016.

There were some utility challenges related to the extraction shaft design and construction, and this led to the TBMs mining in to the unexcavated shaft with exposure and removal of the equipment in the last month.

Ground conditions

The geological conditions were provided to the contractor through Geotechnical Data and Geotechnical Baseline Reports. The tunnel alignment consisted of mixed-face conditions of primarily interstadial sand to gravel along with some intermittent sections of silt to sand, plastic Glacio-lacustrine and plastic till. The depth of cover of the twin tunnels ranged from 10m to 26m.

The upper water table ranged from 5m to 10m above tunnel springline for approximately half of the drives, with corresponding pressurised face tunnelling mandated by contract for the entire length of the drives.

Tunnelling

Tunnelling operations included 10-member TBM crews and a supporting surface crew working two 12-hour working shifts, five days a week. The tunnel working compound was shaped as a long and narrow rectangle and was bisected by a construction roadway. The contractor established a one-way flow of construction traffic and operations from the west to east end of the site. A tower crane offloaded site deliveries (including tunnel segment stacks) to the surface storage area or down into the launch shaft onto an awaiting TBM service train. A continuous conveyor system was implemented to transport the excavated muck from the TBM to the muck pit at surface minimising muck handling time and increasing tunnel production. Muck removal operations on surface were conducted during the night shift to minimise traffic congestion within the site and on adjacent roadways. A wheel wash station was installed for vehicles exiting the site. The compound also included a water treatment plant and warming house for segments during the winter months.

Average mining time for a 1.5m ring length for both tunnel drives was 35 minutes, while the average ring build time was 25 minutes. Advance rates were analysed for each ground type but did not differ significantly across the various conditions. Tunnelling through the full face silt to sand conditions achieved the highest advance rates of 78 mm/minute while mining through the plastic Glacio-lacustrine layers achieved the lowest at 54 mm/min. Daily and weekly working production for each drive averaged approximately 18m and 90m respectively. These high production rates are a testament to the reliability of the TBMs and effective operations and planning of the contractor, though it must also be noted that a high-quality of tunnelling (addressing both ring build and settlement control) accompanied these consistent rates. Peak daily production reached 41m for Drive 5 and 47m for Drive 6.

The calculated EPB target pressures ranged from approximately 1.5 to 3.0 bar and were to be maintained within +/- 0.3 bar. To manage EPB, the project team implemented an alert system with e-mail notifications when EPB pressures dropped below set limits. The contract required target EPB pressures to be maintained at all times, including during weekend shutdowns. The contractor chose to achieve this by implementing an automatic bentonite injection system that continuously monitored and injected bentonite into the TBM chamber when required. Overall, EPB was operated and managed effectively by the project team.

Continuous tail shield annulus grouting was also carried out during TBM advance to control settlement. Evidence of successful annulus grouting for the tunnels was witnessed several times throughout the project while excavating the open-cut shafts at emergency egress buildings, and during both cross passage construction and proof drilling operations. Effective grouting was also confirmed by proof grouting operations, which resulted in minimal injection volumes. During construction, settlement monitoring was conducted by surveying a wide array of instrumentation including approximately 850 settlement monitoring points (SMPs) and 800 building monitoring points (BMPs). Overall, settlement above the tunnel was controlled effectively below the review and alert levels that corresponded to volume loss of 0.5 per cent and 1 per cent respectively. Successful settlement control in the primarily cohesive sandy conditions was a result of effective EPB and annulus grouting management and controls implemented by the project team.

As previously noted, headwalls were installed prior to tunnelling at each end of the future stations, at emergency egress buildings, and for the launch and extraction shafts. In total each TBM mined through 13 headwalls – six secant pile and seven jet grout. The contract specified cutting head interventions after the first 300m, at each emergency egress building and at one mine-through headwall location per future station. The contractor elected to perform three additional cutting head interventions for each drive; one after mining through the launch shaft headwall and two while tunnelling through the plastic till stretches early in the tunnel drives. Though the TBM was equipped with an airlock, all interventions were performed at headwall locations permitting free air entries. In general, the contractor employed a conservative approach to managing cutting head wear and tool changes. The average distance between cutting head interventions was 330m with an average of 18 cutting tools changed per intervention on both drives. See Figure 1 for further cutting head intervention details. A cutting head intervention was not performed at the second emergency egress building location due to difficulties with water inflow and face stability. This decision was supported by a cutting head wear assessment that determined the risk of excessive tool wear was low should the TBM proceed to the next specified intervention location.

State-of-the-art TBMs were procured and delivered for the project. Tunnelling contract documents explicitly defined TBM availability, setting clear minimum criteria for the contractor to use in planning and estimating the work. CAT technicians were on-site providing assistance with TBM commissioning, disassembly and removal, and troubleshooting with minor equipment breakdowns. Additionally, the construction management team employed an experienced in-house TBM specialist to oversee and work collaboratively with the contractor to resolve issues. This proactive and integrated approach led to overall TBM availability performance well in exceedance of expectations defined within the contract. This demonstrated the successful performance of the TBMs and the quality and experience of the contractor’s personnel operating the machines, as well as the effective implementation and management of controls specified for the owner-procured machines.

TBM Removal

In early March, the first of the East Tunnels TBMs was removed from the extraction shaft, east of Yonge Street. Despite the cold brisk air many interested community members were on hand and passersby stopped to witness the exciting occasion. Preparations are currently underway within the shaft for removal of the second TBM, which will involve translating the TBM shields laterally to align with the shaft lifting window. The second and final TBM is expected to be removed from the extraction shaft in April.

Shafts, emergency egress buildings and cross Passages

The open-cut boxes for the future emergency egress buildings, launch shaft and extraction shaft were constructed using traditional methods with primarily secant piling temporary support of excavation incorporating steel struts and walers. The open-cut boxes for the emergency egress buildings were fully excavated only after the passage of the TBMs to maintain sufficient cover for the pressurised EPB tunnelling. Decking was installed over approximately half of the emergency egress building and extraction shaft excavations to maintain traffic flow.

The hand-mined cross passages were 4.5m in length with a final lined diameter of 3.7m, providing a connected passageway between the twin-bored running tunnels. Cross passage construction consisted of the following activities to enable hand mining: dewatering from the surface and tunnels, grout injection for ground stabilisation umbrella, and installation of steel propping rings to support the saw-cut doorway opening in the PCTL. Hand mining commenced in a heading and benching excavation sequence using steel liner plate and ribs for initial support, followed by contact grouting, application of a shotcrete regulating layer, sprayed waterproofing membrane installation and casting of reinforced concrete final lining. The cross passage construction was successful and achieved maximum settlements well below contract specified review levels.

Next Steps

As of April, one of the East Tunnels TBMs has been removed from the extraction shaft while the other is in preparation for removal, the emergency egress buildings have been completely excavated and the cross passages final cast-in-place concrete linings are completed. The tunnel box structure of one of the emergency egress buildings is completed and work is progressing for the stairway shaft and corridor connection to the surface. The next milestones will be to continue with the handover process of the remaining tunnel sections, along with the emergency egress buildings and cross passages to the Crosstown Stations Contract. The handover will facilitate the continuation of the next phase of construction for the 25 stations of this momentous project. The Crosstown is expected to be in service in 2021.