Piling
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- Piling
Building strong foundations
Piling is an important construction technique that provides the strength and stability needed to support transit infrastructure. Whether it's for stations, elevated guideways, bridges or other essential components of a project, creating a sturdy foundation allows these structures to support the loads they will encounter – including trains, riders, and the structures themselves.
This time-tested method has been used for centuries to stabilize the ground for excavation and construction. While modern materials and technologies have advanced significantly, the fundamental principles of piling are largely the same.
There are several piling methods and techniques typically employed in modern transit construction. Each type is selected based on the unique needs of a project, including factors like the weight the piling needs to support, and the conditions of the soil and groundwater where new infrastructure is being built.
For major structures like transit stations and bridges being built in urban environments, methods like bored piling and slurry walls are commonly used. These techniques are designed to handle heavy loads and stabilize areas with loose soil or high groundwater levels while minimizing impacts to communities during construction.
For less-intensive work, especially during the early stages of a project, other piling methods are often used that are more suitable for lighter loads or temporary support.
The information below is meant to provide a high-level overview of methods commonly considered for major components of Metrolinx projects. Please note that other methods may be used depending on the unique locations and needs of the projects we are delivering.
A close-up look at a piling rig, the powerful machinery used to create deep foundations for transit infrastructure.
Bored piling
This construction method is used to create deep, strong foundations for our projects. It involves drilling a hole into the ground, which is then filled with reinforced concrete to form a sturdy support column, called a pile.
Excavated material is removed using a large drill called an auger and concrete is poured in, often around a steel reinforcement cage to provide added stability. The piles extend deep into the ground, reaching soil or bedrock layers that can bear heavy loads so that the weight of the new structure above is supported safely and securely. Depending on the needs of the project, hollow steel tubes called casings may be installed before reinforcement cages are added and concrete is poured to help keep the surrounding soil in place.
Watch to learn more about what piling is and why it's such an important first step in delivering new transit like the Ontario Line.
You’ll often see equipment like drill rigs, cranes, excavators, and concrete pumps in action during piling, along with concrete trucks coming and going to support the work.
Piling is an important part of many projects underway as we work to expand and improve transit across the region.
Piling work in downtown Toronto to support Ontario Line construction.
Slurry walls
Slurry walls, also known as diaphragm walls, are a specialized form of piling used to create water-tight, reinforced concrete walls deep in the ground. These walls are particularly effective for building foundations in areas with high groundwater levels or unstable soil.
Learn more about the process of creating slurry walls to support construction of a new Ontario Line station.
The process of building slurry walls starts with digging a trench, one section at a time, using heavy machinery like backhoes or hydromills. As the trench is excavated, a bentonite slurry (a mixture of clay and water) is poured in to keep the walls of the trench steady and prevent groundwater from seeping in.
Reinforced steel cages are then lowered into the slurry-filled trench to add strength to the final structure.
The next step involves pouring concrete into the trench, which pushes the slurry to the surface as it fills up. The displaced slurry is collected and filtered before its reused for other sections of the trench. The result is a solid, reinforced concrete wall deep underground that acts as both a retaining structure and a water-tight barrier.
Get in touch
If you have questions about work on a Metrolinx project being built close to you, please reach out to the Community Engagement team in your area:
