Construction of a New Sanitary Sewer: "Wishing it Into Place"

Storer J. Boone, Dirka U. Prout, Dan Beadle, Kevin Brown, Jan Svihra

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Instrumentation and Monitoring

ABSTRACT: This paper describes design and construction of a sewer through a historic urban district. The late 19th century brick buildings already exhibited damage from historic settlement, building modifications and weathering. During design, other subsurface risks led to abandonment of trenchless methods and underpinning or conventional excavation support systems also presented unacceptable risks to the tenants and building owners. Use of novel cut-and-cover excavation support systems, close communication and cooperation between the sewer owner, designer, construction manager, geotechnical consultant, and contractor combined with detailed monitoring resulted in successful construction where displacements of the historic structures were controlled exceptionally well and the sewer was virtually 'wished it into place" under difficult conditions. RÉSUMÉ Cet article décrit la conception et la construction d'un égout, à travers un quartier urbain historique. Les bâtiments en brique de la fin du 19ème siècle, démontraient déjà un endommagement en raison des tassements historiques, des modifications du bâtiment et de l'altération. D'autres risques souterrains ont mené à l'abandon de l'approche sans tranchée. La reprise en sous-œuvre ou les méthodes d'excavation conventionnelles présentaient également des risques inacceptables pour les locataires et les propriétaires. L'utilisation des systèmes de support novateurs de tranchées, la communication et la coopération entre le propriétaire d'égout, le concepteur, le gestionnaire de construction, le consultant géotechnique et l'entrepreneur, à l'aide d'un programme de surveillance détaillé, ont contribué au succès du projet. Ainsi, les déplacements des bâtiments voisins ont été contrôlés de façon exceptionnelle et l'égout a été virtuellement installé par simple souhait, sous des conditions difficiles. 1 INTRODUCTION The city of Toronto has embarked on an ambitious project to rebuild a large, formerly industrial area into high-density residential, commercial, and green spaces along the city waterfront. As part of this project upgraded sanitary sewer lines were needed to connect new buildings to the existing city system. One of the sewer lines had to run along a street partly lined with historical structures. In 1969, Dr. Ralph Peck cleverly used the phrase '–we shall now wish a circular tunnel into existence–' to illustrate the mechanics of tunnel lining design, followed by the practical understanding that '–real tunnels cannot be wished into place.' Because of the pedestrian traffic, commercial activity, underground space already highly congested with utilities and concern for the historic buildings, consideration had been given to constructing the sewer line using 'trenchless technologies' in a desire to 'wish the tunnel into place' so as to minimize disruption at street level. Geotechnical investigations, however, indicated that trenchless methods could be obstructed by subsurface debris and misaligned because the invert elevation was to be near the interface between soil and rock. Therefore, a decision was made to proceed with open cut excavation using a specially designed support system and detailed monitoring of the excavations and neighbouring buildings. 2 NEW SEWER The sewer was required to support development of a portion of a new neighbourhood planned for re-zoned industrial lands on the shores of Lake Ontario on the eastern edge of Toronto's downtown core. The lands slated for re-development are located within the drainage area for an existing sewage pumping station, which the City was also expanding to service the lands. The start and end points of the sewer alignment were therefore fixed, and the vertical alignment was constrained by the elevation of the existing pumping station. Once it was determined that it was not feasible to upgrade the existing sewer to accommodate the ultimate occupancy of the precinct, the alternative of twinning the sewer with a parallel sewer was reviewed. The streets that the sewer needed to be built along are relatively narrow downtown streets, originally built and serviced over 100 years ago that have become congested with large-diameter storm sewers and utility lines (gas, electrical, telephone, cable, fibre-optic, and others). As such, there were limited options for developing the horizontal alignment of the proposed sewer. Once the design was finalised, the

RÉSUMÉ: TRUCTION OF A NEW SANITARY SEWER: 'WISHING IT INTO PLACE' Storer.J. Boone, Dirka U. Prout ,

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Cite this article:
Storer J. Boone; Dirka U. Prout ; Dan Beadle; Kevin Brown; Jan Svihra (2014) Construction of a New Sanitary Sewer: "Wishing it Into Place" in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper113,author = Storer J. Boone; Dirka U. Prout ; Dan Beadle; Kevin Brown; Jan Svihra,title = Construction of a New Sanitary Sewer: "Wishing it Into Place",year = 2014}