The Eglinton Crosstown Project - Jet Grouting Challenges and Achievements

L Clatworthy

Dans les comptes rendus d’articles de la conférence: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: GROUND IMPROVEMENT - I

ABSTRACT: The construction of the Eglinton Crosstown Light Rail Transit (ECLRT) Project in Toronto involves the construction of 6.3 m excavated diameter twin tunnels in advance of shored excavations for future cut-and-cover station construction. For this schedule-driven sequencing, shoring headwalls with soft tunnel eyes are typically installed in advance of tunneling and the tunnels are mined through the headwalls and station footprint. However, the construction of the headwalls using traditional secant piles quite often requires time consuming and complex utility diversions. For the ECLRT, an innovative approach to the shoring design has been introduced whereby a jet grout block is constructed at tunnel horizon below the utilities at a location where headwalls would otherwise be constructed, to provide a shoring element that will be incorporated into the future deep excavation shoring. The jet grouting ground improvement technique was implemented to stabilize glacial till soils, particularly saturated silts and sands that exhibit flowing behavior when exposed. Additionally, jet grout blocks were specified at several cross passage locations for control of groundwater and excavation stability. The paper discusses the design of shoring using the jet grout block concept, its specification and implementation in a congested urban environment and, the effectiveness of the blocks during tunneling. The paper also identifies a number of lessons learned for future applications of this unique approach.

RÉSUMÉ: Le projet de la ligne de transport léger sur rail Crosstown soutènements nécessaires à la réalisation des futures gares souterraines par tranchée couverte. La séquence normale de tunnels traversant les murs de soutènement et la zone de la gare. Toutefois, la réalisation de tels murs de soutènement par la méthode des pieux sécants requière souvent des déplacements de services compliqués et longs à mettre en place. Pour ce projet ECLRT, une approche innovatrice de la conception des soutènements des sols a été utilisée par laquelle un bloc jet grouting est réalisé aux extrémités de la gare dans la zone des tunnels sous le niveau des services souterrains qui sera ultérieurement intégré au système de soutènement des sols de la fouille profonde. La méthode du jet grouting a n comportement boulant quand mis à découvert. Des blocs jet grouting ont aussi été requis à plusieurs passages transversales reliant les deux tunnels afin de contrôler les eaux souterraines et stabiliser les sols durant leur creusement. Cet article discute de la conceptig fie également un certain nombre de leçons apprises pour de futures applications de cette approche innovatrice unique. 1. INTRODUCTION Managed by Metrolinx, the ECLRT is located in Toronto, Canada and is a 19km rapid transit line beneath Eglinton Avenue. It comprises 11km of twin bored tunnels split into two contracts; the first (west) contract runs from Keele to Yonge and the second (east) contract from Yonge to Brentcliffe. Hatch Mott MacDonald (HMM) was appointed by Metrolinx to complete the tunnel design, cross passage design and station headwall design for the ECLRT. Tunnel excavation for the west and east contracts commenced in 2014 and 2015, respectively. Tunnels have been excavated using Earth Pressure Balance (EPB) Tunnel Boring Machines (TBM) through a series of glacial tills, interglacial and glacial lacustrine deposits approximately 20mbgs (metres below ground surface). The grain size of the native ground encountered varies from stiff clays and very dense silts to loose sands and gravels with occasional cobbles or boulders. Over eighty percent of the soil within the tunnel horizon comprised gravel to sand and sand to silt. Both tunnels are below the groundwater level and the TBM was designed to resist an average EPB target pressure of 0.7 bar (max 2.0 bar). The saturated conditions and permeable nature of the granular deposits allow for an

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