Some 14,785 tunnel rings. 88,500 tunnel segments. An exceedingly tight schedule. With dimensional and quality control requirements so exacting, tunnelling expert Chris Smith of CRS Consultants called it "the tightest speci? cation I’ve ever had to meet."

It’s all for the new Eglinton Scarborough Crosstown LRT (ECLRT), a cornerstone of the City of Toronto’s transit infrastructure upgrade. Managed by Metrolinx, an agency of the Government of Ontario, the ECLRT will traverse Eglinton Avenue running east/ west through the heart of the city — linking 54 local bus routes, three subway stations and the provincial GO commuter rail system. To reduce disruption, it will run underground for 10km at the busiest part of Eglinton, requiring the construction of two 10km tunnels at 5.75m in diameter.

The project is generating a lot of buzz in Canada’s largest city and surrounding suburbs. The Greater Toronto Hamilton Area (GTHA), comprised of the City of Toronto, the City of Hamilton and four regional municipalities (Durham, Halton, Peel and York) is Canada’s largest urban region and one of the country’s fastest growing areas. More than six million people live in the area today and the population is forecasted to grow to 8.6 million people by the year 2031.

The GTHA’s existing network of regional transportation corridors was developed several decades ago, and the infrastructure is old. Congestion is a serious problem, with the average daily commute taking 80 minutes. Construction of rapid transit, which averaged approximately 135km per decade from the 1960s to the 1980s, all but ground to a halt for two decades because of a lack of investment. There was conflict in the various levels of government over who should pay for and how these major projects should be funded. This lack of investment contrasts sharply with what is happening elsewhere in the world. In the US, most large cities have invested heavily in rapid transit. Madrid — only slightly smaller than the GTHA — has built more rapid transit facilities during the past decade (88km) than all of the current Toronto area subway and light rail lines combined (77km).

For the city to be competitive globally, something had to change. Metrolinx created a plan, The Big Move, that outlines a common vision for transportation in the GTHA. The Premier of Ontario and the minister of transportation committed CAD 11.5bn (USD 11.2bn) to begin the implementation of The Big Move, and now Metrolinx is upgrading the province’s transportation infrastructure. Fast.

And that speed meant they needed to change the way things are done in order to keep pace with their ambition.

Tender
Contract ECLM6-2 Supply of Precast Concrete Tunnel Lining Segments was released for bid to prequalified companies in late 2010. The manufacture of the tunnel lining segments was not part of the tunnelling contract. Tunnel segment manufacturing was a single contract.

Metrolinx chose to put the manufacturing in the hands of actual manufacturers in a complete reversal of the traditional approach. Historically in this business, tenders were released for contractors to bore the tunnel and supply the tunnel liners. So now, gone are the days of contractors having molds made and partnering with precasters or establishing a temporary facility to make the liners. That practice meant struggling to either amortise the cost of the molds on that first job, or try to find additional jobs where those expensive molds could be put to use. And when considering that cost-recovery effort had to be accommodated in the lowest bid and tunnel boring is a high-cost, risky business, tunnel lining segments were not the contractors’ focus.

That’s why Metrolinx and the Toronto Transit Commission (TTC) released a tender for manufacture of the tunnel lining segments directly. The moulds to make the segments were to be purchased by the successful bidder but they would be Metrolinx property at the conclusion of the contract. The quality assurance program for the segments requires QA checks by the manufacturer and by an on-site Metrolinx representative. Once the tunnel segments are approved by Metrolinx, they are available for shipment to the jobsite. The contractor only needs to verify that there has been no damage during shipment and accept the delivery.

Setting new standards
It’s clear that Metrolinx has a long-term strategy on transportation and that allowed Munro, the successful bidder for the manufacture of the tunnel lining segments, to develop a long-term strategy for the manufacturing. The company was awarded the CAD 78.2M (USD 76.1M) contract to manufacture the 88,500 tunnel lining segments.

Located about an hour’s drive north of Toronto, Munro manufactures a complete line of concrete and steel infrastructure products. All manufacturing is done 100 per cent indoors, under 100 per cent controlled conditions.

Munro had previously manufactured tunnel lining segments the traditional way, as a sub to a tunnelling contractor to produce segments for the 510m-long, 2.7m diameter Coxwell Sanitary Trunk Sewer By-Pass, a tunnelled by-pass around a damaged, major sewer line in Toronto. But the ECLRT contract meant an opportunity to invest in a new manufacturing line and processes. That meant adding an additional 100,000sq. ft (9,290sq.m) to the existing manufacturing facility and two additional concrete mixers to the computer-controlled batching system. The production line is a European-sourced carousel system that was improved to increase efficiency by having fewer stations with lower operator intervention. The system is installed flush with the factory floor to lessen worker fatigue and increase safety.

The accelerated delivery schedule of the ECLRT project required the production of 28 rings per day over a period of two and a half years. To achieve this, the entire manufacturing process had to be vertically integrated. There had to be complete control over all components of the process — from inspection of raw materials to manufacture of rebar cages, casting of segments, curing, storage and delivery. Using outside suppliers for any component of the process was deemed to be too risky given the tight production schedule and quality control requirements.

Standard reinforced rings (rebar cages) were specified. The technical and quality specifications were extremely stringent, including RFID tagging of each segment and a two-stage curing process. The primary cure requires a maximum concrete temperature of 55 oC and the segments must have 15MPa strength so they can be lifted from the mold with vacuum suction. The secondary curing process is a five-day cure in 100 per cent humidity. The automated double-cure process ensures the segments are fully cured and at full strength before they are stored in the yard or shipped to the jobsite. These are considerations necessary to ensure the concrete is fully cured before it is stored outside during cold Ontario winters.

Going robotic
A new rebar manufacturing and handling facility was designed and developed in order to manufacture the reinforcement cages. This was the most aggressive and innovative step taken by Munro in the manufacturing plan, and it was done to be able to consistently achieve the quality and production requirements of just-in-time supply to the filling station. The cage specification calls for 100 per cent pass rate on rebar tests. If reinforcing cages were manufactured externally and orders of reinforcing cages were delivered in batches from a supplier, any quality control issues (such as reinforcing cage dimensions being out of specification) would cause serious production delays running into days and possibly weeks. Also, by bringing the manufacturing of reinforcing cages in-house, Munro decided to apply several technological innovations to the process to ensure that welds on the cages and dimensions of the cages were consistent. And the company implemented in-line production testing to ensure quality at each of the production stages.

The process starts with coiled steel and ends with the ‘Brady Bunch,’ six robots that weld the tunnel segment reinforcing cage using both vision and touch, a major innovation that results in a robotically welded rebar reinforcing cage, ready for insertion into the tunnel lining segment mould.

The Brady Bunch welds the tunnel segment reinforcing cage in 244 places to 100 per cent weld strength.

Dimensional consistency and quality of welds in tunnel segment reinforcing cages has long been a problem in the industry. The need for accuracy and strength of welds is extremely important so that the installed tunnel ring functions as the design engineering team intended. Now with the assurance through robotic welding, that can be guaranteed. Each segment is tagged with a RFID tag after the cage is produced. The tag contains all the information about the segment, allowing complete traceability of materials and production. The system even has GPS capability that can locate a single segment in the yard.

A new approach
The rigid timeline, the precise quality control specifications and the large production quantity drove innovations that can now be used on future manufacturing of tunnel lining segments for other tunnelling projects.