CSST - Combined Sewage Storage Tunnel
Ottawa, Canada
TBM rock (Double Shield)
Construction method
6.000 m
Excavated length
3.00m / 3.71m
Internal Diameter/Excavation
1 TBM
TBM number
The Combined Sewage Storage Tunnel (CSST) is a key component of the Ottawa River Action Plan, developed to improve river water quality by reducing wastewater discharges during periods of intense rainfall.
The project consists of two underground tunnels designed to operate both as wastewater collectors during normal conditions and as stormwater storage tunnels during peak flow events, helping prevent direct discharges into the river.

DRAGADOS delivered the scheme using a Double Shield tunnel boring machine, constructing two consecutive rock tunnels lined with precast concrete segments reinforced exclusively with steel fibres.




The development combines hydraulic infrastructure, environmental protection, and advanced tunnelling technology within one of the most important wastewater management projects undertaken in Ottawa.
Project data
Project data
·
6 km total tunnel length
·
64,500 m³ excavation volume
·
3.00 m internal diameter
·
3.71 m excavation diameter
·
Dual-function collector and storage tunnels
·
1.9 km North–South tunnel
·
4.1 km East–West tunnel
·
Excavated using a Double Shield TBM
·
Fibre-reinforced segmental lining







