Ottawa Combined Sewage Storage Tunnel (CSST)

Owner
City of Ottawa
Client
Dragados Tomlinson JV
Cost
$232 million CAD
Timeframe
February 2016 — May 2020
Services performed
TBM segmental lining design, rock mass grouting design and engineering support services during construction. Value engineering efforts helped increase TBM tunnelling performance by reducing probing ahead.
Description
The CSST project is part of the Ottawa River Action Plan to greatly reduce the frequency of sewage overflows during storms entering the Ottawa River. The tunnels will hold up to 43,000 m3 of sewage overflow which will be treated and returned to the river gradually. The project comprises 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 such as odour control facilities. Dr. G. Sauer & Partners supported the contractor with the feasibility study on TBM utilisation. Reduction of probe drilling requirements increased TBM excavation rates, by pre-excavation grouting criteria justification amongst others.
Geology
The alignment of the tunnels mainly crosses limestone formations with laminated black shales of varying thickness. The rock is overlain by glacial till, glaciofluvial deposits and fill.
Location
Ottawa, Canada

Highlights

  • DOUBLE SHIELD TBM CROSSING FAULTS AND BEDROCK VALLEY IN OPEN MODE
  • GEOTECHNICAL RISK MANAGEMENT FACILITATING SCHEDULE SAVINGS
  • ROCK MASS GROUTING OF MAJOR FAULT AHEAD OF TBM ARRIVAL FOR SCHEDULE BENEFITS
CSST Map (http://ottawa.ca)

CSST Map (http://ottawa.ca)

East West Tunnel under construction (3m tunnel ID)