An interview with John Sherstobitoff, Principal, Seismic & Structures on winning the 2017 Canadian Consulting Engineers' (CCE) Schreyer Award for the Port Mann Water Supply Tunnel Project
Can you please give us a brief overview of the Port Mann Water Supply Tunnel project?
The project is a new potable water supply tunnel underneath the Fraser River. It includes a kilometer long tunnel encasing a steel pipe, vertical shafts some 55m deep at either side of the river – one in Coquitlam, and one in Surrey, BC.
The tunnel was needed as the existing water pipeline was deemed likely to fail in a low to moderate level earthquake thus cutting off this water supply to residents south of the river. The intentions were to harden the system to ensure water delivery to residents after an earthquake that exceeds a “code level” earthquake. This was an excellent community project with regard to post-earthquake resilience, and a challenging project from a technical point of view because of the seismic criteria and the resulting predicted large soil movements.
The Schreyer Award is presented to the project that best demonstrates technical excellence and innovation. Can you tell us about this?
There were a number of elements to this project that captured the attention of the judges. First, the tunnelling work encountered some of the highest water pressures ever seen in Canada. As a result, a unique design was required in order to move the tunnelling machine successfully through the varying soils beneath the river bed. Secondly, for the level of earthquake we were designing for, we needed to account for the fact that the soil on either side of the river is predicted to move some six-metres towards the river due to liquefaction. Thus we needed to design for this movement in the vertical shafts and the steel piping therein and have the system still be able to deliver water to the residents. The final design is one where the shaft will yield and deform significantly, but not fail.
The key to the design is that the steel pipe inside the shaft is fixed only at the base, 55m down and at the valve chamber wall at the surface. It too will yield significantly. This was what really made the project unique, there’s never been a shaft and steel pipe designed to yield and we put both of them together.
Another interesting component of the work was the type of concrete shoring used during excavation. Prior to the construction of the shafts, excavation work is carried out where a cylinder of concrete must be installed to hold the soil back as one excavates. For the first time at these depths, the concrete cylinder used did not have any reinforcing steel in them. This saved money. Imagine being 55m below the surface with a ring of concrete around you with no reinforcement - you are relying on hoop action – this was unique in itself.
What does winning the Schreyer award say about Ausenco and their advocacy of innovation?
It says a lot. We focus on bringing innovation to every project and for every client. For this particular project, the level of innovation is a result of a combination of several components. First, we are an industry leader in the use of advanced analytical tools. One can only push innovation when you’re confident in the analytical tools you are using. We performed sophisticated 3-D, non-linear analysis and sensitivity analysis to truly understand the situation. We also benchmark our work against the many projects we have already completed, and use this to our advantage.
Secondly, our experts are active in their respective spheres – attending/presenting at conferences around the world and working with researchers to continually expand their field of knowledge and stay current on recent advances in engineering and construction. Thirdly, I must acknowledge the willingness of our clients to trust and work with us. Without them, these ideas and innovations would not be a reality.
How do you feel about winning the top Canadian Consulting Engineering award?
Personally, I feel fantastic! I’ve been involved with this project from the very beginning – from the conceptual design – right through to the construction of the project. I accepted this award on behalf of many people – this was a huge team effort involving Ausenco, sub-consultants, contractors, and the client. Congratulations to all!