Launch of the veteran Robbins TBM in Toronto, Canada. Photo Credit: McNally Construction Inc.

It’s a long-standing question in the world of tunneling: Which TBM has been operating the longest? What makes it so durable?

In May 2011, I visited the site of the Centennial Parkway Sanitary Sewer Tunnel in Hamilton, Ontario, Canada to find some answers.  The rock portion of the tunnel, located in the shale of the Niagara Escarpment, is being bored by a Robbins Main Beam TBM in operation since 1968.  The 2.7 m (8.8 ft) diameter machine was first used for a Hydroelectric Tunnel in Tasmania, and is now owned by McNally Construction, who has used it on multiple sewer tunnels in Toronto and Ottawa since 1972.

The original Main Beam TBM, manufactured by Robbins in 1968.

I arrived at the Centennial Parkway site on a sunny Friday afternoon along with Tunnels & Tunnelling North America editor Nicole Robinson, where we were greeted by McNally Project Sponsor Dave Bax and Field Technician Kenny Baxter.

After giving us some safety instructions, we were handed full rubber suits and boots.  “You’re going to need these,” said Kenny. “It’s muddy on the shaft floor, and the material is red.  It gets everywhere.”  A quick look around the jobsite confirmed his statement—red clay-like material caked nearly everything, from trailers to trucks to boots.

The red clay material being loaded in muck cars.

We climbed down a long ladder into the shaft, and were given a tour of the small diameter tunnel.  Kenny explained that the ring beams and wooden lagging installed at the tunnel entrance were due to the softer clay material encountered at that point.  The rest of the rock portion of tunnel was being supported with rock bolts and steel straps. “The shale material is being recycled to use as brick.  The clay was used by a local gun club for berms on their grounds.”

Single track muck cars rolled out as we walked out of the tunnel, carrying more heaps of reddish shale, before they were lifted by a crane and dumped on the surface.