Ottawa Construction News staff writer

Ottawa’s $232.3 million Combined Sewage Storage Tunnel (CSST) project – one of the city’s largest and yet least visible infrastructure projects – remains on budget, but is experiencing delays, says Alain Gonthier, the city’s director of infrastructure services.

“The CSST remains on track for commissioning in 2020,” he wrote in an April 18 memo. “Heavy construction was anticipated to be completed late in 2019 and is now projected to extend into 2020. The delay (approximately six months) is associated with shaft and starter tunnel excavation at Site 10 (Chamberlain Ave. and Kent St.) during the summer/fall of 2017 and, more recently, challenges in final assembling and commissioning the tunnel boring machine (TBM) for tunnelling.”

“TheTBM is beginning to progress at the rate originally anticipated,” he wrote. “As with any complex construction project, opportunities to recover and/or mitigate this construction delay over the next 10 months are being pursued and evaluated.”

The project’s contractor is Dragados Tomlinson Joint Venture. The CSST reduce the frequency of combined sewage outflows to the Ottawa River, and reduce basement flooding risks for several neighbourhoods, while improving the flexibility and redundancy of major downtown collector sewers, specifically the 50-year-old Interceptor Outfall Sewer and the 80-year-old Rideau Canal Interceptor Sewer.

The work involves constructing two interconnected tunnels to store a combination of surface runoff and wastewater. The north-south tunnel runs under Kent St., from Chamberlain Ave. to behind the Supreme Court of Canada, and the east-west tunnel extends from Lebreton Flats to Stanley Park, generally under Slater and Cumberland streets.

In addition to the tunnels, construction includes 15 major access shafts and four odour control facilities.

Site-specific progress:

Site 10 (Chamberlain Shaft – Chamberlain Avenue at Kent St.)

• Construction commenced in September 2016 at Site 10 – the main construction staging area for the NST and the first launching point for the TBM.
• A gantry crane stationed over the 23-metre-deep shaft is removing excavated material and lowering precast concrete tunnel segments for transport via train to the TBM.
• Work to support tunnelling operations is continuing 24 hours a day, six days a week, in accordance with the applicable noise by-law exemption.

North-South Tunnel (NST)

• Tunnelling using the TBM commenced in December 2017, and has progressed slowly northward, under Kent St., toward the Ottawa River.
• Tunnelling paused in order to complete assembly and commissioning of the TBM; now, production has accelerated to approximately 20 metres per day, with more than 500 metres of tunnel currently installed.
• Tunnelling continues 24 hours a day, five days a week, in accordance with the applicable noise by-law exemption, with excavated material stockpiled at Site 10 and trucked off-site during daytime hours.

Site 6 (North South Tunnel Overflow/Kent Street Outfall – Ottawa River Pathway)

• Site preparation at Site 6, the TBM’s first exit point, was undertaken in February 2017, and active construction commenced in October 2017.
• The rock slope face has been excavated in preparation for the TBM’s arrival.
• A water-control berm and temporary by-pass for the existing Interceptor Outfall Sewer have been installed, and construction of two chambers and a new outfall is underway.
• Work is, at times, continuing 24 hours a day, six days a week, in accordance with the applicable noise by-law exemption.

Site 5 (EWT Outlet/Rideau River Collector RC Diversion – New Edinburgh)

• Construction commenced in March 2017 with construction staging in Stanley Park and establishment of a site access, egress and trucking route.
• In Stanley Park, the excavation of an 18-metre-deep shaft – the TBM’s second launching point – is complete, and mechanical excavation of a starter tunnel is underway. Another smaller access shaft is also fully excavated, while a third is nearing completion. This work is continuing 24 hours a day, six days a week, in accordance with the applicable noise by-law exemption, with excavated material stockpiled and trucked off-site during daytime hours.
• Interior and exterior finishing of a new odour control facility in the park is near completion and pending commissioning.
• Excavation of a fourth shaft to connect existing infrastructure at the intersection of Queen Victoria St. and River Lane commenced in December 2017, with shoring work and rock removal underway.

Site 1 (West End Shaft – LeBreton Flats)

• Construction commenced in February 2015 under a cash-allowance, in co-ordination with O-Train Confederation Line construction, to complete necessary modifications and connections to existing sewer infrastructure, as well as begin constructing the TBM’s final exit point – a 19-metre-deep shaft.
• Excavation of the shaft is complete.

Site 3A (Rideau Canal Interceptor Diversion/Drop – Confederation Park)

• The secant shoring system was completed in December 2016, and the site was reinstated prior to Winterlude 2017. Construction re-commenced in March 2018 with the installation of instrumentation, tree protection and site fencing/hoarding.
• Excavation a 22-metre-deep shaft is underway within the park, with work continuing 24 hours a day, six days a week (in accordance with the applicable noise by-law exemption).
• A temporary off-street cycling connection has been constructed along the eastbound Laurier Ave. ramp to the Queen Elizabeth Driveway.