Ward & Burke sets new Canadian microtunnelling record

Approximately 5,040m was microtunnelled, including oblique lengths under commuter rail tracks, while open-cut was used for around 630m. Overall, final microtunnel drive lengths of 800m, 731m, 501m, 641m, 821m, 950m and 1,132m were achieved.

A Herrenknecht AVN 1800 was used for the 1,132m drive, with a VMT SLS system to navigate a horizontal curve of 500m radius over a distance of 228m and a very flat continuous grade of 0.02%. Ground conditions comprised extremely soft clays and silts at the start of the drive with SPT values between 0 and 10, then transitioning into harder glacial tills containing cobbles and boulders. Water pressures ranged between 0.7-1.2 bar and a mixed-ground cutting head was chosen as the most suitable for the changing conditions. No cutterhead interventions were required during the drive.

Low jacking forces were used for all microtunnel drives: the TBM pushed into the reception shaft with 300t of jacking force and without using any of the five intermediate jacking stations. Rescue shafts or other interventions were also not necessary. Supporting the TBM was a 500m3/hr separation plant but throughout the drive it was not necessary to treat or remove liquid waste from the site.

Work is continuing with the installation of permanent pipework and chambers. Also required are modifications and upgrades to existing pump stations to accommodate the new linear infrastructure, with final commissioning expected in autumn 2021. Despite working through COVID-19 restrictions, the project is currently four months ahead of schedule, with all shafts and microtunnels having been completed within a year of site mobilisation. GHD was the owner’s designer and contract administrator on the project.