Geotechnical Investigation Program for the Don River and Central Waterfront Wet Weather Flow System

Mark Bruder, Daniel Cressman, Robert Mayberry

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

Session: Tunnelling and Deep Excavations

ABSTRACT: The City of Toronto is implementing the Don River and Central Waterfront Project to reduce Wet Weather Flow into Lake Ontario, the Don River, and Taylor Massey Creek. Black & Veatch in association with R.V. Anderson Associates Limited has been contracted by the City to complete preliminary design of the entire project, detailed design of Stage 1 construction, and to scope/manage the geotechnical investigation (currently underway). The geotechnical program includes drilling over 280 boreholes with a comprehensive sampling/testing schedule to define the subsurface conditions and mitigate risk with the design/construction of the tunnels/shafts. Routine and specialized rock/soil sampling and testing is included to define the geotechnical parameters that are critical in the design of tunnels/shafts. This paper focuses on general subsurface conditions, development and management of the geotechnical program, engagement of stakeholders, and the usage of collected data in defining geotechnical risks.

RÉSUMÉ: debits par temps pluvieux dans le lac Ontario, la rivière Don, et le ruisseau Taylor-Massey. Black & Veatch en association avec R.V. Anderson Associates Limited a été engagé par la Ville pour compléter la conception préliminaire du projet, la conception détaillée de la construction de l'étape 1, et la portée et la gestion de l'enquête géotechnique (actuellement en cours). Le programme géotechnique comprend plus de 250 forages avec un calendrier complet d'échantillonnage et de test pour définir les conditions du sous-sol et atténuer les risques liés à la conception et la construction des tunnels et des puits. géotechniques qui sont essentiels dans la conception des tunnels et des puits. Cet article se concentre sur les conditions générales du sous-sol, le développement et la gestion du programme géotechnique, l'engagement des parties tion des risques géotechniques. 1 OVERVIEW OF THE DR&CW WWF SYSTEM The City of Toronto (City) is implementing the Don River and Central Waterfront (DR&CW) Project to reduce Wet Weather Flow (WWF) into Lake Ontario, the Don River, and Taylor Massey Creek. A primary goal is to de-list the Don River and Inner Harbour as an International Joint Black & Veatch in association with R.V. Anderson Associates Limited (design team) has been contracted by the City to complete preliminary design of the DR&CW Project and detailed design of construction Stage 1, and to scope and manage the geotechnical investigations. The geotechnical program is currently under way and is being completed to support preliminary and detailed design of all five construction stages. The DR&CW Project encompasses design and construction of the following components: 22 km of tunnels in both rock and soft ground with 12 shafts and 27 connections, seven detention tanks, and a high rate treatment facility at Ashbridges Bay. The DR&CW Project is expected to cost $1.5 billion and be implemented over the next 25 years in the following five construction stages: Stage 1: Inner Harbour East (IHE) and Lower Don (LD) Tunnels (i.e. Coxwell Bypass Tunnel), Stage 2: Taylor Massey (TM) Tunnel, Stage 3: Offline Storage Tanks, Stage 4: Inner Harbour West (IHW) Tunnel, and Stage 5: WWF Connections (WWFC) to tunnels. For Stages 1, 2, and 4, refer to Figure 1 for an overview of tunnel properties. Shaft internal diameters range from 8 m to 22 m, and the maximum shaft depths in soil and rock are 60 m and 43 m, respectively. 2 GENERAL SUBSURFACE CONDITIONS Across all five construction stages of the DR&CW Project, quaternary soil deposits overlie shale bedrock of the Georgian Bay Formation. The soil, often called overburden or soft ground, was deposited during the Wisconsinan glacial period. It is a complex distribution of glacial till layers separated by interstadial deposits of sands, silt, and clays. These

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