LRT track could corrode bridge, report warns
New, eight-lane structure cost $4.5 billion
A light-rail line planned for the new Samuel De Champlain Bridge in Montreal runs the risk of corroding the $4.5 billion structure, a risk authorities say they’re taking all the necessary measures to avoid.
The eight-lane bridge opened in July of this year, replacing the older Champlain Bridge that was compromised by the overuse of road salt and had to be replaced before it failed.
The proposed LRT line will run in the centre of the new span with a 1500-volt direct current power supply through overhead wires, but there is a risk that could lead to the electricity leaching into the surrounding bridge structure and causing corrosion over time.
“A DC power distribution system for transit applications is subject to stray currents leaking into the underlying infrastructure and may cause premature corrosion,” said a report on the issue that was sent to the project’s chief engineer and included in an access to information request.
The report goes on to say that the risks can be mitigated with special railway ties, sensors to detect any stray current and regular maintenance to ensure the track stays clean.
Lama Khodr, a spokesperson for Infrastructure Canada, said they have worked closely with the bridge builder Signature on the Saint-lawrence and the builders of the transit network, the Réseau express métropolitain (REM) to ensure the corrosion doesn’t happen.
“Infrastructure Canada and Signature on the Saint-lawrence (SSL) worked closely with the engineering team for the REM project to ensure that the light-rail transit system to be integrated into the central corridor of the bridge will not pose any harm to the structure of the bridge which has been built to last 125 years,” she said in an email to the National Post.
Khodr said they’re still working with authorities in Montreal to ensure that all the necessary steps are taken to avoid any damage to the bridge when the LRT is installed. She said the bridge design was finalized before the final design of the LRT was known.
Corroded infrastructure is an all-too-familiar tale in Montreal. The old Champlain Bridge, built in 1962, is actually the second newest of five spans linking Montreal to the South Shore, but it corroded prematurely because it was built without proper drainage.
Builders at the time did not envision the use of road salt on the structure, and the span was built in such a way that it was impossible to remove sections of it and replace them. The corrosion, caused by a water and salt mix, damaged the bridge badly, and by the time authorities moved to address the drainage situation in the 1990s, most of the damage had already been done.
The federal authority maintaining the older bridge poured in more than $500 million in recent years just to keep it open and operational, while the new span was completed. The bridge is now closed and due to be demolished by 2022 at a cost of $400 million.
Speaking for CDPQ Infra, the division of the Caisse de dépôt et placement du Québec building the REM, Jean-vincent Lacroix said the builders are well aware of the stray-currents issues.
He said the REM is not the first light-rail system to be built over a bridge and techniques to deal with the phenomenon are “tested, proven and effective.”
“The phenomenon of stray currents can be compared to water leaks,” Lacroix wrote in an email. “In electricity, electrical losses related to an electrical device are called stray currents. These currents do not always follow the planned path (by the catenary and by the rails); they may sometimes, in small quantities, look for another way to circulate.”
He said they’re confident they can deal with the situation both on the Champlain and on the five new bridges they’re building as part of the project.
Lacroix said builders are installing metal components to collect the currents on bridges and will install monitoring tools to detect any lapses in the protection systems put in place.
“We are working in collaboration with the designers of the SSL bridge and Infrastructure Canada, and we are very confident that our preventive design measures will avoid the accelerated corrosion of the new Samuel-de Champlain Bridge, and all the other infrastructures of the REM,” he wrote. “We can therefore affirm that there will be no acceleration of corrosion to the bridge caused by the REM.”