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2016WinterShotcreteEMag

2015 Outstanding Repair and Rehabilitation Project Société de transport de Montréal—Metro Yellow Line Tunnel Repairs By Kevin Robertson, Patrick Giguère, and Ntam Nda-Ngye The Montreal Metro is an underground metro system and the main form of public transportation in the city of Montreal, QC, Canada. The Metro, operated by the Société de transport de Montréal (STM), was inaugurated on October 14, 1966. It originally consisted of 26 stations on three separate lines, but now has 68 stations on four lines totaling 43.0 miles (69.2 km) in length, which serves the entire greater Montreal area. 1.2 million passengers now ride the system daily. The Yellow Line is the only metro line that runs between the island of Montreal and the south shore. The project (Metro Yellow Line Tunnel Repairs) was released for tender on September 23, 2013, and was awarded to Construction Interlag Inc. of Saint-Léonard, QC, Canada. Construction Interlag Inc. is a civil construction company with expertise in all aspects of concrete repair and rehabilitation. Their shotcrete team, which employs several ACI Certified Nozzlemen, has over 75 years of combined shotcrete experience in the civil and mining markets. Engineering Scope The initial feasibility study was completed by an outside consulting engineering firm. However, an internal STM engineering group took over the design work, conducted a delamination survey, and performed a finite element analysis of the tunnel walls. The STM engineering team identified approximately 6500 ft2 (600 m2) of overhead area requiring removal and replacement, most of which ranged in thickness from 18 to 35 in. (450 to 900 mm) (Fig. 1). The sequence for the work to be completed was specified as: 1. Removal of deteriorated and delaminated concrete; 2. Installation of rock anchors and wire mesh; and 3. Placement of shotcrete (dry-mix process). The majority of the work was undertaken in a 2.5 mile (4 km) stretch of tunnel between the Berri–UQAM station and the Longueuil–Université De-Sherbrooke station. This stretch of tunnel runs underneath the St. Lawrence River. To complete the project with minimal disruption to the Montreal commuters, it was decided that the work schedule would be spread over 207 nights with the majority of the concrete replacement (shotcrete) being completed over 25 weekends. The shotcrete placement was split into two phases in an effort to further accommodate transit riders during some of Montreal’s major arts and cultural events, not the least of which was the Montreal Grand Prix. During the time when the stations were closed, a shuttle service that bypassed the construction zone was offered to the public. Shotcrete Materials The material specification called for a prepackaged, high-quality shotcrete mixture that would provide long-term durability, so the STM engineers specified the same parameters that are used by the MTQ (Quebec Ministry of Transportation) in their shotcrete specification. Key aspects of the specified mixture design were: 1. Air entrainment: The most important performance durability criteria remains the determination of air void distribution, as per ASTM  C457. In-place, hardened shotcrete requires an average air void spacing factor of under 0.0118 in. (300 μm), with no individual results over 0.0125 in. (320 μm). In a dry-mix shotcrete application, air-entraining admixture should be added in powdered form and preblended with other components at the point of manufacturing. The shotcrete mixture producer should have a proven track record producing prepackaged, air-entrained, dry-mix shotcrete and should be able to provide ASTM C457 test 30 Shotcrete • Winter 2016


2016WinterShotcreteEMag
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