Collapse Of Route 112
Unparallelled reconstruction in Québec
In August 2009, a major landslide occurred at the Lac d’amiante Mine, causing the complete closing of a section of Route 112, located between Saint-Joseph-de-Coleraine and Black-Lake in Thetford Mines. Thousands of tonnes of rock that had served as the road bed ended up at the bottom of the open pit mine, making all traffic impossible.
Because this highway infrastructure is considered of key importance for the region, its relocation became a priority for the Ministère des Transports du Québec.
For this large-scale mandate, the Norda Stelo/SNC-Lavalin Consortium designed and monitored the work on this road site surrounded by enormous waste rock piles, where the majority of the excavated materials were contaminated with asbestos. This project also lead to the development of a temporary bypass road, complying with the standards of a national highway, over a distance of 10.3 km.
Considering the contamination of the materials and the proximity of the mine, the protection of the public and the workers against the dangers of asbestos was a priority for our engineers.
Thus, ongoing cooperation with the CNESST allowed the development of a new approach for mass excavation, performed in the open air in the presence of asbestos. Several preventive measures were developed and applied on the site to reduce any risk of asbestos contamination:
- Regular air quality measurements on the job site and in the neighbouring municipalities;
- Adaptation of the work according to the wind direction;
- Wetting the materials before excavating;
- Machinery operator cabs always maintained at positive pressure;
- Self-contained breathing apparatus with filters;
- Compulsory shower when leaving the jobsite;
- Compulsory washing of all machinery leaving the jobsite.
This proven methodology today serves as a reference in the field for eventual road work involving asbestos or any other contaminated material that may be airborne.
Moreover, various measures were undertaken and planned by our team to mitigate the project’s environmental impacts. We removed many contaminated materials from the environment, such as the pavement of the former highway, which contained asbestos.
The disposal of the contaminated excavation materials was also examined in depth to avoid the risk of dispersal in the environment and contamination of the population, wildlife and flora. To protect the public and future generations, we decided to bury these materials in the shaft of the former mine.
Several safely developed embankments, measuring more than 100 metres long and 50 metres high, were necessary to design Route 112. Due to the proximity of the waste rock piles and their heterogeneous composition (rock, gravel, silt, clay, alluvium), we deployed exceptional measures to ensure the safety of road users. Embankments and tiers were constructed to reduce the rockfall risks. Drainage downflows were fashioned to allow water to flow while limiting erosion of the embankments, a complex risk given the varied composition of the soil and the drop. We should also mention that the free passage of ichthyofauna was carefully taken into account through the development of culverts with weirs allowing fish to cross. Landscaping of the embankment bordering the new highway also involved distinctive effort by planting trees and shrubs, while we removed invasive exotic plant species very present on the site from the environment.
Considering the very nutrient-poor soil, we used an experimental method to favour the growth of vegetation. Our consortium, in collaboration with the MTQ and the mandated laboratory, chose to recover residual materials from wastewater sludge to fertilize the surfaces of the embankments. This innovative technique had only been tested on small areas with gentle slopes. For this project, the technique was deployed on a large scale over long steep slopes, contributing to improve the sector’s visual appearance.
Finally, to avoid disturbing the lives of people in the region beyond what was absolutely necessary, we planned the jobsite carefully to allow access at all times for local businesses and residents for the duration of the work.
Competence and ethics guided the design of this huge road project to eliminate future landslides as much as possible and make the road safe and sustainable. The decision to build a three-layer pavement structure with a thickness never attempted before, using sustainable, non-contaminated materials, from the frost line, shows the importance attached to the development of a sustainable and stable road for the benefit of the population, while favouring sound use of public funds.
The new section of Route 112 was opened to traffic in October 2015. For more than a decade, the population and businesses were compelled to live with a long detour and with the closing of the main road connection between Thetford Mines and Sherbrooke, with all the economic, environmental and social impacts caused by this exceptional situation. Despite immense challenges, citizens today benefit from a safe and sustainable new highway. The entire project was completed in September 2018, at a total cost of $90 million, or $10 million below the budget initially established.