A Tunnel Boring Machine (TBM) is a large, sophisticated piece of equipment used to excavate tunnels for various purposes, such as transportation, utilities, mining, and more.
A Short History of Tunnel Boring Machines
Tunnel Boring Machines (TBM) are not given a second thought these days. However, it is safe to say that our engineering ancestors would be amazed by the sheer size, efficiency, and speed with which they construct our tunnels worldwide.
Tunnel boring machines have revolutionized tunnel construction by allowing for faster and more controlled excavation compared to traditional methods.
Today we look at the evolution of this innovative piece of machinery and how far the technology has come.
Where the Idea of TBM originated
The earliest form of the Tunnel Boring Machine was known as a Tunnelling Shield. The idea first occurred to Marc Isambard Brunel, a French naval officer in England, in 1818. The ecosystems around us often influence great discoveries, and this is no exception. After observing a shipworm, Brunel noticed how their shell plates allowed the worm to work its way through timber and push the sawdust behind it at the same time.
Why not apply the same action when removing soft soil? He set to work building a giant rectangle iron casting that could be pushed forward through the soft ground while construction workers dug the dirt out from the front of the shield. This equipment was used to build the world’s first underwater tunnel under the Thames in London, taking 17 years.
A challenge presented itself when people wanted to build tunnels through hard rock. The tunnelling shield didn’t have this capability. The Wilson Patent Stone Cutting Machine was invented in 1851 and was created to cut hard rock. This machine would cut a 33cm wide circumferential ring, about eight meters in diameter, in solid granite. After advancing into the rock, the machine was removed, miners would then blast the rock from inside the ring. Built from cast iron and powered by steam, the Wilson Patent Stone Cutting Machine worked its way through the rock using roller cutters, which are very similar to what is used in modern TBMs.
For 100 years, advancement in TBM technology proved too expensive, with multiple companies going broke through the experimental periods of their work. Rock tunnelling returned to excavation by drilling and blasting. It wasn’t until the 1950s that James S.Robbins invented the first modern TBM for the Oahe Dam Project in the US. The cutterhead design utilised rows of drag bits and disc cutters to excavate weak shale. The drag bits would cut grooves in the rock, and the roller cutters would break the stone.
His design and experiments bought to light the two basic concepts of TBMs that are carried through to today’s machinery. Based on these two concepts, all modern-day TBMs were invented.
- A rotating cutting head at the front of the machine.
- A circular shield to protect the workers, equipment, and where tunnel support can be erected.
Current TBM Technology
Fast forward to the twentieth century, where the underlying technology and principles of TBMs are the same. However, there are now different variations of machinery designed to cut through specific stone and soil conditions ensuring speed, efficiency and minimising cost.
- Gripper TBM
- Double-Shield TBM
- Single-Shield TBM
- Earth Pressure Balance Machines
- Slurry TBM
- Mixshield Technology
- Pipe Jacking
- Partial-Face Excavation Machine
- Noncircular Shields
A Look to the Future of TBMs
Engineers, scientists, and entrepreneurs believe that the future of tunnelling is in improving the speed and costs efficiency of the machinery.
For example, Tesla and SpaceX founder Elon Musk believes that the future of our transport systems is moving all underground due to population density and lack of space to build more roads and rail above ground. Such transport systems would require massive amounts of tunnelling. Due to this belief, Musk has started a new venture, The Boring Company. They have concluded that our current TBM technology is too slow and are looking at advancing the power output of the machines. A snail digs 14 times faster than our TBMs. The Boring Company is looking to catch up with the snail.
Other companies are looking to remove the need for the TBM stopping as each ring of precast segments is being installed. This stop-start of the machinery is the most time-consuming part of the tunnelling process.
No matter the advancements, the need for tunnelling and moving transport infrastructure underground will always be required.
Read about West Gate Tunnel Project tunnel boring machines here
Read about Cross River Rail Project tunnel boring machines here
Some interesting facts about TBMs
One of the most famous TBMs, named “Big Bertha,” was used to bore a tunnel in Seattle, USA. It weighed around 6,700 tons and had a diameter of 17.5 meters. Another notable example is “Bertha II,” used to construct the Alaskan Way Viaduct Replacement Tunnel.
In 2013, a TBM named “S-210” set a world record by excavating 2,807 feet (856 meters) in a single month during a project in Malaysia.
TBMs were used to construct the Channel Tunnel (Eurotunnel), which connects the United Kingdom and France. The tunnel includes the world’s longest undersea portion, and multiple TBMs were used simultaneously from both sides to meet in the middle.
TBMs are favored for urban projects as they significantly reduce surface disruptions and noise pollution, making them a more environmentally friendly option.
Tunnelling powers ahead to construct the 23km Western Sydney Airport metro alignment in Greater Western Sydney.
Western Harbour Tunnel Stage 2 is underway, as a 100-tonne roadheader began its excavation journey from Cammeray to Waverton in NSW.