Canada salutes top class engineering 15 Nov 2018

Metro tunnelling beneath the streets of Toronto, an underground alternative for expansion of a hydro plant in British Columbia and a lifetime career in the service to international geotechnical engineering by Canadian expert Garry Stevenson are the achievements honoured in the 2018 series of the Tunnelling Association of Canada TAC Awards. Presented at the gala evening of the TAC tunnelling conference in Edmonton, Alberta, current TAC President Erik Eberhardt, congratulated the recipients and welcomed them to the Canadian hall of fame of underground engineering and construction.

Winning the Canadian Infrastructure Project of the Year accolade for 2018, the 9.7km of twin running tunnels of the Eglinton Crosstown LRT Project are part of a Can$9.1 billion investment by the Ontario Provincial Government to provide 19km of dedicated LRT service for the City of Toronto along Eglinton Avenue. Developed by Government of Ontario agency Metrolinx, Crosstown is the largest transit expansion in the history of Toronto and is the first LRT line for the city. Upon completion in 2021 it will link regional and local transit, cut travel time along the route by half and will have provide more than a thousand jobs during the construction phase.

The 9.7km of 5.75m i.d. twin running tunnels have been excavated under two contracts awarded to the Aecon Dragados JV for the East Running Tunnels and to Crosstown Transit Constructors JV of Obayashi, Kenny, Kenaidan and Technicore for the West Running Tunnels contract. Tunnel excavation started in 2012 and was completed in 2017 using four EPBMs bought and supplied to the two contractors, along with the segmental lining, by the client. The contracts included construction of TBM launch boxes of up to 130m long x 20m deep; ten cross passages; two emergency exit buildings; 20 station headwalls of either secant piles or jet grouting; and extensive relocation of critical utilities before tunnelling could begin - all within a dense, dynamic urban environment.

Challenges included tunnelling under active passenger rail lines; lifting and transporting two TBM shields in one piece over an active subway line and managing and relocating aging and complicated utilities.

The soft glacial till deposits posed a significant risk of settlement damage to more than 1,400 structures and 800 utilities along the alignment. Settlement was limited to averages of less than 0.2% face loss and the tunnels were completed with no major impacts to any existing infrastructure. Tunnelling adjacent to residential communities representing broad demographics also required effective public engagement and minimisation of stakeholder disruption.

The project started under tight constraints with an urgent need to complete the tunnels for hand over to the follow-on station contract. Considering the scope and complexity of this project, the project team took several steps to make sure the project was delivered and handed over to the follow-on contractor on time and on budget.

As project owner, Metrolinx was responsible for the designer selection process, designer scope definition, contract packaging, tendering and award of project contracts. During construction, Metrolinx contributed oversight of the construction management team, approved contract change orders and payments, reviewed and maintained budgets and schedules, managed quality assurance and was responsible for overall risk mitigation for the project.

Canada based consulting engineer Hatch completed the preliminary project design, assisted in procurement for early works items including purchase of the TBMs and the precast concrete tunnel lining, completed detailed design of the tunnelling contract packages, designed the precast tunnel liners, managed design of utility relocations, and provided the running tunnel contracts with construction management and program management services.

All phases of the construction contracts were the responsibility of the contractors and all work for the contracts was completed within the owner’s project schedule timeline.

Innovations applied for hydro station upgrade

The John Hart generating station replacement project on the Campbell River in British Columbia is worthy of the Innovations Project of the Year for 2018 on several counts. It is the first P3 public-private-partnership project in the power sector in Canada; it creates a more reliable, environmentally friendly, increased capacity underground power station to replace the existing surface power plant installation and required innovative technology to successfully manage an unexpected zone of soft ground geology during drill+blast excavation of the main access tunnel of the project.

Developed by the P3 partners of BC Hydro and InPower BC, an SNC Lavalin single purpose company, the replacement project includes a new intake, a new power tunnel and an underground power station, to replace the three surface penstocks and the existing surface power station. It also increases installed capacity form the existing 126MW to 132MW and includes a new water bypass to provide flow continuity below the generating station and protect the downstream ecological habitat. About 95% of the Campbell River flows through the John Hart generating station.

The P3 team three alternative schemes during the initial phases and convinced the client BC Hydro to include an underground powerhouse as part of the contractor-proposed scheme. The original intention by BC Hydro was to have a surface powerhouse which would have necessitated an extensive steel lined section of the power tunnel. The selected scheme places an underground powerhouse at the location at which hydraulic fracture of the power tunnel would not occur and hence avoids most of the steel lining requirements making it the most economical of the schemes considered.

Among other innovations, the new intake to the power tunnel was tunnelled 6m under the existing 10m high concrete dam. This concrete lined tunnel was integrated with the gate structure to withstand earthquake loads on the combined structure. The analyses for the structure consisted of a non-linear ground structure interaction using finite element software. The lining was designed in two stages – the first was during construction, during which the structure had to withstand the 1:2,475 AEF event. This initial lining consisted of lattice girders at 1m centers and 350mm of shotcrete. The final lining acted in concert with the initial lining and was designed to withstand the 1:10,000 AEF earthquake with an additional 1.2m of reinforced concrete.

The 8m diameter power tunnel, supported with a pattern of rockbolts and steel fibre reinforced shotcrete passed under an existing earthfill dam. The tunnel alignment was located as far upstream and as far into the bedrock as practical to reduce the uplift from the tunnel, now pressurised to the headpond elevation, to an acceptable limit so as to minimise the risk to the 70 year old dam. Significant effort was employed to carry out in-situ hydraulic conductivity tests and seepage analyses to confirm that the additional uplift pressures would be acceptable. A system of piezometers in and around the dam were monitored during pressurisation of the tunnel and confirmed that the additional uplift was, in fact, acceptable.

Contractor for the civil works for the P3 developers was Aecon of Canada with Frontier Kemper of the USA engaged for the tunnel excavation works. A further innovation was used on the project when, after 90m of tunnelling, a buried channel consisting of interglacial sand, gravel and boulders was encountered in the main access tunnel in May 2015. This feature was not predicted during the site investigations and the mining sequence had to switch to an SEM (sequential excavation method) process that made very slow progress.

A parallel exercise to model the feature in 3D using drilling data from the surface, through the face of the excavation and from inside the powerhouse and surge chamber, revealed a path around the feature in solid rock. The excavation was switched back to drill+blast to successfully bypass the buried channel and allow the project to stay on schedule.

A career in geotechnical engineering

The 2018 Canadian Lifetime Achievement Award is presented to Garry Stevenson for his more than 40 years of experience in the design and consultancy for hydro power and underground works projects. His participation at every level of project design of tunnels and rock caverns for hydro power schemes has taken him to important projects the world over. Through mentoring and supervising teams of young and experienced engineers, he has ensured high quality design and good business relationships with owners and clients.

Garry has been an active member of Tunnelling Association of Canada (TAC) starting in the mid-1980s. He performed numerous functions for TAC, including Chair BC Chapter; TAC President 2005-2008; responsibility for revising the TAC bylaws; coordinating student theses award; and serving on nomination committees at various times. Garry supported and mentored young TAC executives during and after his term as President.

Garry is a registered Professional Engineer and Professional Geoscientist in British Columbia and a registered Professional Engineer in Washington State, USA.

Congratulations to all the worthy recipients of the Canadian Tunnelling Association TAC Awards for 2018.