As contractors prepare their final bids for the two major tunneling contracts that are critical to the 8.6km expansion of the Toronto metro, client Toronto Transit Commission (TTC) is busily overseeing preparatory works which will ensure that the new line and six new stations are complete by the end of 2014. “It is a very tight schedule and we are committed to a revenue service date of late 2015,” explains TTC construction supervisor Alan Boden. “Tunnelling has to finish to support the installation of trackwork, systems and station build out so the only way we could guarantee that and ensure that the EPB machines were available at end of the design period was to get them manufactured ourselves.”
TTC is no stranger to tunnelling works. The City of Toronto is home to the country’s first ever metro subway line which was completed in 1953 and ran along the centre of the city from Union Station to Eglinton Station. Over the next 50 years the line expanded to become a network that today has 70 stations dotted along 70km of track, spanning the city both north to south and east to west. The last extension was a 5.5km line with five stations running east to west between Sheppard-Yonge and Don Mills. On this contract TTC procured two TBMs directly from Lovat and saw the benefits of direct action. The same strategy is now being used on the latest extension and along with the EPB machines, procurement of the 9000 Armtec tunnel liners has also been undertaken by TTC. These are now being manufactured in nearby Woodstock.
A head start
Such measures are set to give the successful contractors a headstart once the contracts are awarded. Seven contracting ventures are in the running for the contracts including Spain’s Dragados, Spain’s FCC Construction, a joint venture of Italy’s Impregilo with US Healey, the North American JV including McNally /Kiewit/AECON International with local Akon Contractinga, Spain’s OHL, Austria’s Strabag and Japan’s Obayashi with Flatiron Canadian Kenaidan.
The two contracts cover a total of 6.7km of twin bored tunnels with the CAD 250M (USD 238M) southern package also incorporating Shepherd West station, four cross passages and two extraction shafts. The CAD 350M (USD 333.5M) northern package includes SECM (NATM) construction of a double ended pocket track housing structure where trains can be turned at peak time, compensation grouting for the south end of the new station at York University along with three cross passages and two extraction shafts. “The reason for compensation grouting is that the station within the York University has buildings either end of the station and the Schulich School of Business at the southern end was borderline for tunneling induced ground settlement. Predicted behaviours showed that the settlement needed to be arrested with, compensation grouting was the recommended method,” explains Boden.
Awards for the contracts are just weeks away with the tender for the southern contract closing at the end of September and the northern section at the end of October. “All of the contractors were prequalified earlier this year. And [we] invited them to qualify as station contractors, EPB tunnelling contractors and then specialist sub contractors for compensation grouting and Sequential Excavation Method (SEM) tunnelling,” says Boden.
Geology
The SEM tunnelled section is a modification to the original plans as the triple track required to turn the trains was originally housed at Steeles West station that Boden refers to as a “monster.” Instead the team decided to rationalise the station box by housing the turning point in a DEPTHS located south of the York University Station. “This allows every second train to be turned back at peak periods. We looked at various ways to construct it, with EPB or combinations of EPB with SEM but we decided that it was best to do it all in SEM and so the machines are not tied up by this construction,” Boden explains.
The ground conditions here are stiff clay making it a favourable location for SEM. Along the rest of line ground conditions are all in glacial deposits. Most of the tunnelling is in a very hard schist stiff lower till, or in the very stiff upper till. In places the upper till and lower till are separated by a sand and silt layer, which becomes more prominent and more granular moving north. “The ground water table is within a metre of the surface throughout the alignment so while we have cohesive material it is not so problematic, but the further north we go where the granular material is, there we will face challenges with water issues,” says Boden. In addition the granular material could also contain boulders of any size. “By and large the upper till and lower till are well known geological features to this part of Toronto. The Shepherd Line was constructed in very similar ground conditions but what makes it more of a challenge is the high water table and the granular material further north.”
As EPB machines are being used for the tunnel bores, water ingress will only be an issue for the six station boxes. The team is therefore considering combinations of secant piles and secant pile head walls. “As we move north towards Vaughan we may need to look at some form of bentonite slurry cut off wall,” says Boden.
Stations
Station contracts are set to be awarded in the first quarter of 2011 but a range of other enabling contracts are already underway, such as traffic management and utilities diversions. Key to the programme delivery however is the early construction of the TBM launch shafts for the southern and northern sections. “The project has been very busy for the last 12 months with a series of early construction contracts required to give us a head start on the programme. Two launch shafts are underway, the first to the west of Shepherd West Station on the south tunnels and the second south of Steeles West Station,” says Boden.
These rectangular 22m deep box shafts were awarded to local contractors in March and April. With the south section extending 45m and the second 55m as this is sitting in the future cross over box at Steeles West giving the team more space.
An added complication that the TTC has to contend with is the multi-regional dimension that this particular section of the metro has. Unlike any of the other spurs the new northern link, which runs past York University and on to the City of Vaughan moves from being part of Toronto City to being part of the Regional Municipality of York Region. “It is the first time the TTC has developed outside of the city boundary so there are some interesting challenges associated with obtaining land and permits but by and large it has all gone pretty smoothly,” says Boden.
This explains why the CAN 2.01bn (USD 1.92bn) financing required has come from a variety of sources, from the Canadian federal government (CAN 697M [USD 664M]), the Ontario provincial government (CAN 670M [USD 638M]) and then from both the City of Toronto and the Regional Municipality of York. An executive task force of representatives from both regional and provincial government has been established to oversee the project which extends into York Region to provide high quality rapid transit service in the fastest growing region in the Greater Toronto Area. It is set to take 1,700 buses per day off the roads of Ontario. These currently serve the influx of students attending York University, which stands to benefit greatly from the new metro line known as the York University Line. This extension will also benefit York University’s Keele campus as the community of 40,000 plus people will have a station within the heart of the campus to ultimately reduce the need for bus service.
Looking ahead the next few months are going to be very busy for the TTC, which has major contracts to award alongside the supervision of the works already underway and preparation of tender documents for the stations. But with nearly six decades of experience on metro construction these challenges are being taken in TTC’s stride.
Work is underway preparing the northern TBM launch site The northern bore will have to cope with a high water table and granular deposits A geological section of the project Construction is set for completion in 2014
