In situ stress measurements at the Coxwell Bypass Tunnel along the inner Harbour East and Lower Don River, Toronto, Ontario

Pierrick Altwegg, Eliane Cabot, Sean Maloney, Adam Coulson, Shami Malla, Scott Goodman

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Rock Mechanics II

ABSTRACT: The City of Toronto is implementing the Don River and Central Waterfront Wet Weather Flow System Project to reduce the combined sewer and storm water overflow and improve the water quality. Among others, this project encompasses the design and construction of 22 km of tunnels, in both rock and soils. In 2016, a geotechnical field program was undertaken for the detailed design of the Coxwell Bypass Tunnel. It included 1.8 km of bedrock drilling. A critical part of the testing schedule included 31 in situ stress measurements near the proposed tunnel Obvert and Invert. These tests were performed by overcoring, a stress relief technique, using the USBM Method. This paper will present the test procedure, describe the results obtained, including magnitude and orientation of the stress tensor, discuss a statistical approach and then conclude with the implications of the design.

RÉSUMÉ: La Ville de Toronto a entrepris le projet de gestion des eaux pluviales et sanitaires de la rivière Don et du centre des rives dans le but de réduire les débordements et d™améliorer la qualité de l'eau. Ce projet comprend, entre autres, la conception et la construction de 22 km de tunnels, dans la roche et dans les terrains meubles. En 2016, une campagne d™investigation géotechnique a été menée pour cibler le tunnel de dérivation de Coxwell. Il comprenait 1.8km de forage dans le roc. Une partie critique du programme d'essais comprenait 31 mesures de contraintes in situ à la base et au toit du tunnel. Ces essais ont été effectués par surcarrotage, une technique de relâchement des contraintes, à l™aide de la méthode de l™USBM. Cet article présente la procédure d'essai, décrit les résultats obtenus incluant l'amplitude et l™orientation du tenseur de contrainte, discute d™une approche statistique puis conclut avec les implications sur la conception.

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Cite this article:
Pierrick Altwegg; Eliane Cabot; Sean Maloney; Adam Coulson; Shami Malla; Scott Goodman (2017) In situ stress measurements at the Coxwell Bypass Tunnel along the inner Harbour East and Lower Don River, Toronto, Ontario in GEO2017. Ottawa, Ontario: Canadian Geotechnical Society.

@article{geo2017Paper295,author = Pierrick Altwegg; Eliane Cabot; Sean Maloney; Adam Coulson; Shami Malla; Scott Goodman,title = In situ stress measurements at the Coxwell Bypass Tunnel along the inner Harbour East and Lower Don River, Toronto, Ontario,year = 2017}