Helping Build the Confederation Line: Our Inside Scoop

Our biggest wire sawing job and the largest of its kind in Ottawa was completed this winter for the Confederation Line. The construction of Ottawa’s light rail transit has been underway since 2013, with an expected launch date of November 2018. It’s the city’s largest infrastructure project to date with anticipated benefits like shorter commutes, cleaner air, and a stronger economy. So when we were called in as contractors, CCC Group was excited to get involved.

How We Got Involved

The largest single undertaking of the Confederation Line was to build a traffic-separated downtown tunnel, which would have three stations; Lyon, Parliament and Rideau. These tunnels were built by the Rideau Transit Group (RGT) and Ottawa Light Rail Transit Constructors (OLRT-c), and there was an important question regarding the exits that needed to be addressed. Should the entrances and exits of the tunnel be framed when pouring the concrete or created afterwards? The most cost-effective choice was to do the latter and that’s where CCC Group came in.

Our Work

We were asked to make an opening of approximately 44 x 8 meters at the New Parliament underground station. We did this by slicing up the blocks and creating 26 cut concrete pieces each weighing between 25 and 30 tons (50,000 and 60,000 pounds). We used wire sawing, and core drilling techniques.

We began with core drilling of 57 holes measuring 8 centimeters in diameter and 55 holes of 12 centimeters in diameter to an average depth of 2 meters (6.6 feet) through the concrete tunnel wall. Core drill rigs supplied by Diamond Products were used to make the holes, with the 8-centimeter (3.1-inch) and 12-centimeter (4.7-inch) diameter holes taking an average of three and four hours respectively using bits and tube extensions supplied by Husqvarna and DTT Canada. These holes were used for diamond wire runs and for attaching rigging and lifting equipment once the cut sections were ready for removal.

With all access holes completed, a length of diamond wire approximately 36 meters (118.1 feet) was threaded through two of them—spaced 6 meters (19.7 feet) apart across the width of the roof area—to set up the first loop for a pull cut. We essentially split the tunnel roof into 26 sliced sections. With the wire saw and operator positioned at one side of the cut area and the wire looped through the opposite side, sawing began. The operator made regular adjustments to the speed, tension and water supply as the wire made the 6-meter (19.7-foot) cut across the width of the tunnel to the core hole on the other side.

Cutting thickness began at 3 meters (9.8 feet), decreased to 2 meters (6.6 feet) and back again as the wire moved across the tunnel roof from one side to the other. Each cut took around six hours to complete. We made 14 cuts like this, then an additional three cuts measuring 5 meters (16.4 feet) long where the cutting area narrowed.

With all these cuts complete, the wire saws were set up to make a series of cuts to free the 26 sliced sections. In total, 29 pull cuts were made in widths from 1 to 3 meters (3.3 to 9.8 feet) and each section was rigged and secured by crane. Wire sawing would stop once the section was completely free from the tunnel wall and the crane could lift it out to street level.

In total, we performed 144 linear meters (472.4 feet) of cutting that led to over 700 tons (1,400,000 pounds) of concrete being removed from the Parliament Station site.

The Challenges

The biggest challenge was probably the time constraint of three weeks to complete all wire sawing and remove the cut sections from the site. To complete the work on time we calculated that we would need to keep all three wire saws running 24/7. We also arranged to have a suitable supply of backup equipment and spare tooling to minimize lost time in the event of any malfunctions or breakages. In order to minimize the noise, we used a wire saw that had the ability to cut manageable sections from huge concrete structures with speed, efficiency and low noise and vibration. Lastly, to ensure safety of the plan, engineers were consulted and evaluated the weight of the cut pieces and whether they would be within the crane’s load capacity and if the street above the station could handle the weight of the crane while lifting the loads.

Outcome

We managed to finish not only on time but also within budget and this awarded us with other projects for the OLRT.

“Capital Cutting & Coring has been an asset to our construction teams. Working within the busy capital of Canada and meeting very sensitive deadlines has its stresses, but the cutting contractor helped relieve some of this stress. The complexity of constructing an underground rail system has had many challenges, so working with professionals was the only way to insure a positive result,” explained William Coleman C.E.T. GSC an OLRT-c/RTG Construction Manager