Urban Tunnelling in the City of Ottawa - A Case Study


Urban Tunnelling in the City of Ottawa – A Case Study

Authors:

Philip Reeve, P.Eng., J.L. Richards & Associates Limited, Ottawa/ON
Jonathan Knoyle, P.Eng., City of Ottawa, Ottawa/ON

Abstract: Built in stages between the early 1940s and 1960s, the culvert structure conveying Nepean Creek under Prince of Wales Drive to the Rideau Canal was a combination structural plate corrugated steel pipe and reinforced concrete frame culvert. Renewal was required due to significant deterioration of the structure and erosion at the outlet that caused collapse of the northeast wingwall, and a slope failure in the east embankment. Sliplining alone of this 10m deep, 65m long culvert could not provide the required hydraulic capacity because of the physical restrictions of the culvert’s composite section. After an exhaustive review of renewal alternatives, a solution that included sliplining the existing structure and tunnelling a new 2100mm diameter culvert parallel to it was identified as one that met the hydraulic requirements and minimized disturbance to sensitive environmental features and to the travelling public. It also provided considerable constructability advantages, as the work could be sequenced to allow flow to be maintained by gravity through the existing culvert during tunneling, and then through the completed tunnel during sliplining. Prince of Wales Drive is an urban arterial roadway with status as a “Scenic Entry Route” into Canada’s capital city. The watercourse being conveyed under the roadway through the culvert drains directly into the Rideau Canal, a World Heritage Site. The soil conditions were mostly highly variable embankment fills as a result of general urbanization over the years. The unique setting, performance requirements, and soil conditions presented significant challenges during design and construction. This paper reviews those critical elements as a case study of the challenges and inherent risks of tunnelling in a sensitive urban environment, and explores the pragmatic measures implemented to mitigate those risks and to manage unanticipated conditions during construction.

Publication Date: 2018

Presented at:
NASTT’s 2018 No-Dig Show Palm Springs, California
March 25-29, 2018 | Paper Number: MA-T6-04


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