Final TBM breakthrough for Ottawa's Combined Sewage Storage Tunnel (CSST)

Thursday, October 3rd, 2019

The 3.7 m diameter TBM constructing Ottawa’s Combined Sewage Storage Tunnel (CSST) successfully completed the east-west drive in September 2019. The north-south drive was completed in summer last year.

Final TBM breakthrough at Site 1

The CSST project is part of the Ottawa River Action Plan and will greatly reduce the frequency of sewage overflows during storms from entering the Ottawa River. The project consists of the design and construction of two TBM tunnels running east-west and north-south along 6.2 km in total, and multiple shafts and support buildings.

CSST Overview map

Contractor Dragados Tomlinson Joint Venture (DTJV) was awarded the $ 232 million CAD contract in 2016 and the CSST will be in operation in 2020.

The DTJV celebrating the final TBM breakthrough at Site 1

Dr. Sauer & Partners provided the TBM segmental lining design, the rock mass grouting design for the crossing of the Rideau bedrock valley and continues to provide engineering support services to the DTJV during construction.

For more project information visit