The South Surrey Interceptor: A microtunneling milestone in North America

The original SSI was constructed in the early 1970s to convey sewage from South Surrey, White Rock, and Langley to the Annacis Island Wastewater Treatment Plant. The regional public utilities commission, Metro Vancouver, began twinning the SSI in 1999 to increase capacity and safeguard the surrounding environment from sewer overflows.

Stantec successfully helped Metro Vancouver design Phase 1 of the project, which was completed as an open cut in 2016. Phase 2 of the project came with a set of several challenges—a stretch of line beneath a key intersection and surrounding industrial parks was particularly demanding.

So, in 2016, Metro Vancouver brought us back to help alleviate some of these issues. How? By designing the largest diameter microtunneling project that North America has ever seen.

Tunneling in four drives

Designing wastewater infrastructure is complex.

When the SSI was initially built, it was done through open-trench methodologies. Due to urban development in the region, open-cut installation was no longer an option. We had to implement tunneling technologies that required a three-metre diameter reinforced concrete pipe with an external diameter of 3.6 metres.

The project was initially designed with only about 400 metres of microtunneling, constructed in two drives with an open-cut segment in between. Then the contractor on the project, Ward & Burke, had the idea to microtunnel all 800 metres in four drives—talk about value engineering! Obviously, Metro Vancouver loved the idea and we redesigned the project accordingly.

We accomplished the installation in four segments:

• Drive 1 – 370 metres long with a curved-drive, primarily through the Fama Business Park, included crossing 54A Avenue 
• Drive 2 – 110 metres long, proceeding into the Benchmark Business Park
• Drive 3 – 40 metres long, repositioning the MTBM within the Benchmark Business Park
• Drive 4 – 285 metres long, with a reverse curve beneath the Panorama Business Park to the reception shaft, including the crossing of busy 152^nd Street

Thanks to a detailed plan—and exceptional collaboration with our project partners—Phase 2 tunneling was successfully completed in mid-2019. 

What sets the SSI apart from other tunneling projects?

There are many factors that set SSI Phase 2 apart from other microtunneling projects. As we mentioned earlier, it is the largest diameter micro-tunnel completed to date in North America. The MTBM was upsized to an excavated diameter of 3.68 metres. But what else sets this project above the rest?

1. The project utilized the versatility of curved pipe jacking in order to facilitate construction through both industrial parks. The use of the curved drives significantly simplified construction by reducing the need for additional easements in Drive 1 and consolidating Drive 4 into a single, long drive
2. There were several areas where the tunnel was mined near existing office buildings and utilities, and where cover above the pipe was fairly low. These factors made slurry pressure, grouting considerations, MTBM guidance, and settlement monitoring critical. Stantec was able to help Metro Vancouver by providing construction phase services to monitor important parameters and document progress of the work
3. The project implemented an innovative contractor-proposed design change post-award to more efficiently complete construction to microtunnel all four segments of the pipeline
4. An environmental assessment of the project was conducted during the design phase and updated during construction. Provincial requirements for disposal of soils containing naturally occurring metals changed during the construction phase of the project. This resulted in the need for additional environmental investigation. Our environmental team quickly performed this work. Fortunately, the microtunneling approach greatly reduced construction and environmental impacts.

A milestone for microtunneling in North America

The $19-million SSI Phase 2 project illustrates how microtunneling can be used successfully to complete large-diameter, curved-pipeline installations in urban areas efficiently, while minimizing disturbance and environmental impacts. For the community of South Surrey, microtunneling was the best option with minimal disturbance to the community. The decision to construct the entire project using microtunneling proved to be successful. If the project had been open cut, the amount of material that would have had to be disposed of at an appropriate landfill (due to the change in disposal limits enacted by regulators) would have resulted in significantly higher project costs. 

All four microtunneling drives were successfully completed by June 2019, and most manholes have been set in the launch and reception shafts. After tunnel completion, the SSI Phase 2 project won two major awards from the Tunneling Association of Canada and the North American Society for Trenchless Technology. It was also short-listed for Project of the Year by Trenchless Technology Magazine.

The full length of the SSI is expected to be fully operational in 2022. View Metro Vancouver’s project summary video.