Tunnelling innovation goes below and beyond
At a glance
Imagine two fast-growing cities. One is plagued with gridlock traffic, challenged urban transportation networks, compromised underground infrastructure (water and sewers), is continually faced with reconstruction projects to meet the status quo and is not properly adapted to address climate change.
The other city moves its citizens with ease to their destinations in a well-choreographed transportation plan. In addition, it has utilities planned to accommodate and manage future growth. As a result, its existing infrastructure is resilient and it’s a popular place to live, work and play.
The difference? The second city has become strong at delivering complex projects underground. They learned how to deliver on subways, roads and rail tunnels, and below-ground utilities, including sewage treatment and collection, water treatment supply, fiber-optic networks and electrical cabling.
Yes – Together, we can make this a reality
Recent developments in underground technologies help planners, engineers, operators and other professionals provide effective solutions under more varied circumstances. This means they can share ideas and opportunities with municipal leaders to build in a different way. So, together we can transform systems and make this a reality for a wider variety of programs and communities.
Over the last 30 years, technological improvements have rapidly progressed with high production rates and more manageable risks. Since ancient times, we have been digging by hand to provide transportation, sewage and water supply projects. These methods were conducive to working in favourable conditions with little congestion or utility interference. However, when challenges arose, it could take a herculean effort with considerable risk to overcome problems. Later, infrastructure, including subways, rail lines, and telecommunications networks, joined the underground environment, making the shallow buried real estate highly congested and more difficult to construct new works.
The earliest of these systems were built with “cut and cover” techniques – open cut with trenching, often along a street, installing the infrastructure, and covering it up again. Some builders continue to use the “drill and blast,” drilling into the rock underground, packing the hole with explosives, and removing the rock blasted away, while others choose to use high performance Tunnel Boring Machines.
The most significant changes have come with the equipment development; from Horizontal Directional Drilling (HDD), Microtunelling Boring Machines (MTBM) and Tunnel Boring Machines (TBMs) the improvement with equipment has resulted in higher productivity with more controlled outcomes. These new machines can all be outfitted with a rotating cutter head that chews through the rock or soft soil, extruding the waste materials. They can travel increased distances and larger diameters, preserving both the built and natural environments while delivering new infrastructure without major disruption.
HDD is increasingly used to install new sewer, water, electrical lines and other smaller tunnels. They generally start from 100 mm in diameter, reach up to 1.5 meters and traverse distances beyond 2.0 kilometres. This helps municipal leaders provide better services with fewer downsides. For example, instead of cutting a trench through a busy roadway, under rivers or under a railway line to replace or install new infrastructure, it is now convenient to use HDD to lay the new infrastructure with minimal impact on the natural and built environment.
MTBMs are generally larger, starting at 600mm in diameter and reaching up to 3.2 metres in diameter. They can create utility tunnels for buried infrastructure such as water sewers, electrical cables and industrial services. These can commonly reach increasing distances of up to 1.5 kilometres and satisfy curved geometry while operating through a wide range of highly varied ground conditions.
TBMs are generally larger, up to about 20 meters in diameter and can create tunnels for storm water conveyance, sanitary pump stations, subways, roads, railways, hydroelectric power and ocean outfalls.
Considerable improvements in recent decades have increased the size and length of tunnels, built more quickly, with more reliability and lower cost. They’re also now able to deal with a broader range of ground conditions, including high water tables, fractured rock, coarse-grained sediments and other challenging volatile ground conditions. The equipment is more maneuverable, able to curve alignment for the tunnel to avoid obstacles such as difficult ground and utilities already present. They can go under buildings, rivers and through mountains with predictable results.
Engineering better social and community outcomes
Perhaps more important for many city residents, the work can be done in a way that reduces the disruption, noise and traffic congestion that plagued many previous underground projects.
Take, for example, Canada’s first subway was constructed in Toronto in 1954 and was built with cut-and-cover that blocked successive parts of Yonge Street, one of the City’s busiest roadways, for months at a time.
Changes in TBM technology allow current extensions to the Yonge North, Toronto subway to be done in a less disruptive way. GHD plays a leading role in advancing the design of 7.4 kilometres of the Yonge North subway extension. This crucial work will aid in limiting the need for shafts dug down from the surface along that distance and helps avoid disruption to the congested residential and commercial community overhead. The added benefit for the City will be great resiliency and higher capacity.
Additionally, when our client, York Region, needed to construct a 5.4kilometer (3.38 mile) tunnel to build a resilient, sustainable sewage solution with minimal disruption to the community and the environment, we delivered. We designed a two-pass system to transfer sewage flow and allow maintenance to be done with no service interruptions, utilizing the most recent microtunnelling technology. The York Durham Sewage System Forcemain Twinning is an award-winning project completed in just 18 months and contains two of the longest curved microtunnels in North America. Delivering a state-of-the-art forcemain with minimal disruption to the public was the goal, and now it is ready to service the community for years to come.
Another way engineers can help provide positive outcomes is by responding to citizens’ concerns about underground construction. This might include showing how the project will manage any risk of vibration or settlement that might damage building foundations and then monitor the project to see that safe limits are not exceeded, or the ground is amended beforehand to avert potential challenges.
Many city leaders have noted that public transit hubs have become a social benefit in their own right. Many residents and developers like the idea of being just a short walk to a subway station. This, in turn, attracts high-rise residential development, retail and other commercial activity. The result is a thriving, vibrant, diverse and productive community for all.
Meet Bradley
Meet Keivan
His extensive knowledge includes various tunnel and trenchless construction methods, shaft sinking and dewatering projects involving tunnel boring machines (TBMs), microtunnel boring machines (MTBM), earth pressure balance machines (EPBM) and other types of tools, machinery, and technologies. With familiarity in designing tunnels for highly sensitive crossings of highways, gas lines, rivers, railways, and public urban areas, Keivan is a professional in implementing long-distance tunnels, projects in densely populated areas, stakeholder and public coordination and tunnel and shaft cost estimation.
He is also knowledgeable about tunnel contractor capabilities, available tunnelling equipment, municipal requirements for trenchless work, areal background ground condition and the history of regional tunnel projects and critical triggers in each area.