Tunnel Atwater

Located near the Atwater market, the Atwater tunnel in Montreal runs under the Lachine Canal, linking downtown Montreal to the borough of Verdun and Highway 15.

The tunnel is 240 metres long and consists of two tunnel tubes, each with two lanes and a sidewalk. The structure was built in 1952, half a century ago, and since then has only had minor repairs.

Groupe Sguin was retained by the city of Montreal in 2000 to assess the tunnel and draw up plans for restoring it.

There were many technical challenges. The project cost $20 million, but this was was less than one third of the cost of building a completely new structure.

Structural rehabilitation

Various techniques in concrete were used to repair the structure and make it resistant to corrosion from de-icing salts. Most of the concrete surface up to 10 cm deep was replaced with a new high performance concrete. Shotcrete was used on the ceiling. Zinc sacrificial anodes were added to remove sodium chloride ions from the rebar. The anodes reduce the localized corrosion of the reinforcing steel and extend the life of the concrete patch repair for 20 years.

The engineers incorporated new safety features, such as adding a sill to the base of the sidewalk railings, and a collision absorber at the base of the portals to the tunnel. They specified new pumping equipment to cope with stormwater flooding and infiltration from the canal. The existing piping that was still in good condition was used to collect rainwater and divert it to the sewer system rather than into the Lachine Canal, thus helping to meet stringent environmental standards.

LED and HPS lighting system

The tunnel lighting had to be completely redefined to conform with today’s lighting standards. Groupe Sguin suggested using a new and innovative system of light-emitting diode, or LED, technology that has been developed by a young Quebec manufacturer, Dellux Technologies. LED lighting is better known in variable message display lighting. It requires little maintenance and gives high energy savings.

The LED lights function continuously 24 hours a day. In the interior zone, which is half the tunnel’s length, the system provides the required two candelas of illumination per square metre at night and the required four candelas per square metre during the day.

However, in tunnel lighting, higher luminance levels are required at the entrances during daylight hours in order to avoid drivers being blinded by the sudden change as they move from bright daylight. The solution at these transition zones was to use a hybrid system during daylight hours that incorporates high-pressure sodium lamps to supplement the LED lighting.

The LED luminaires in the tunnel have a 130,000-hour life, which means it should be 15 years before they need replacing. The lamps are so efficient they consume only 7.5% of the energy drawn by the entire lighting system. They are installed on the ceiling, 4 metres above the roadway, spaced about 3.7 metres across to correspond to the centre of each traffic lane. The sidewalks are lit by asymmetrically arranged high-pressure sodium type III lamps.

LED luminaires are intelligent devices that self-report their conditions to the control system. Parameters like internal temperature, LED age statistics and power consumption are transmitted and used by the controller to calculate the required light output. The system can detect high levels of dust deposits, for example, and promptly readjust the intensity of the LED luminaires. The high-pressure sodium lamps are also linked to the control system by current sensors. This allows the system to detect, any power deficiency in the lamp circuits and alert tunnel authorities if relamping is required.

The Atwater tunnel is the first in the world to be equipped with an intelligent lighting system controlling both LED luminaires and high-pressure sodium lamps with current sensors. The city of Montreal has since decided to install LED luminaires in two more tunnels, Saint-Marc and du Fort.

Owner/Client: City of Montreal

Prime consultant: Group Sguin Socit d’Ingenierie, Montreal (Rene Sguin, ing., Gino Lanni, ing., Richard Marchand, ing., Alain Deroy, tech., Hubert Dubois, ing., Jean-Marie Tardif, tech., Denis Thivierge, ing., Francois Frigon, ing., Claude Ladouceur, tech.)

Contractor: Construction Concordia

Other key players: Dellux Technologies (LED lighting)