TUNNELING AND TUNNEL BORING MACHINE
UNDERWATER TUNNELS
How are underwater tunnels built?
In 1818, a French engineer invented a device that enabled workers to tunnel under rivers without having mud and water ruin their efforts.
Posted 02.11.2002 at 5:40 pm 1 Comment
In 1818, Marc Brunel, a French engineer, invented a device that enabled workers to tunnel under rivers without having mud and water ruin their efforts. His "tunnel shield" was a rectangular cast iron wall with dozens of small shutters. Workers opened the shutters one at a time and dug out a few inches of dirt. Then the whole shield was pushed forward using screw jacks. As the shield lurched ahead inches at a time, the workers behind it constructed a thick, brick lining that became the shell of the tunnel. It took nine years to finish a 1,200-foot passage below the Thames River in London-the first underwater tunnel in the world-but Brunel was knighted for his feat and engineers around the world began adopting his idea.
Variations on the tunnel shield helped create some of the greatest underwater passages in the 20th century, including New York's Holland and Lincoln tunnels. To counter the intense pressure above the tunnels during construction-which caused flooding and structural collapses-engineers installed a system of airtight seals to keep the air pressure as high as possible under the river. Workers spent much of their day just compressing and decompressing. Though many suffered from decompression sickness, overall worker safety was greatly improved.
The Ted Williams Tunnel, which connects South Boston to Logan Airport, illustrates the most modern method of underwater tunneling-the immersed tube. First, workers dredged a 50-foot trench along the floor of
EXAMPLE:
Vital Statistics:
Location: Lancashire County and Manchester, England
Completion Date: 1776
Length: 274,560 feet (52 miles)
Purpose: Canal
Setting: Rock
Materials: Brick
Engineer(s): John Gilbert, James Brindley
Beneath the old
Francis Egerton, the third Duke of Bridgewater, wanted a canal to transport coal from his mines at Worsley to
Work started in 1759 as small teams of skilled miners cut into rock by hand, using only picks, hammers, shovels, and drills. Later on, they used gunpowder to blast through the hard ground. The canal was carved at a downward sloping angle, a design that allowed gravity to pull mining boats through the majority of the long, underground chambers. In 1776, the canal was extended an additional 30 miles, from
Here's how this tunnel stacks up against some of the longest tunnels in the world.
(total length, in feet)
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Tunnel boring machine
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A tunnel boring machine that was used at Yucca Mountain nuclear waste repository.
A tunnel boring machine (TBM) is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through hard rock, sand, and almost anything in between. Tunnel diameters can range from a metre (done with micro-TBMs) to almost 16 metres to date. Tunnels of less than a metre or so in diameter are typically done by horizontal directional drilling rather than TBMs.
Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods in rock and conventional 'hand mining' in soil. A TBM has the advantages of limiting the disturbance to the surrounding ground and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable to use in heavily urbanized areas. The major disadvantage is the upfront cost. TBMs are expensive to construct, difficult to transport and require significant infrastructure. The biggest is built by Herrenknecht AG of Schwanau, Germany to dig the 57 km Gotthard Base Tunnel. It has a diameter of 9.58 meters.
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[edit] History
Cutting shield used for the New Elbe Tunnel.
Top view of a model of the TBM used on the Gotthard Base Tunnel.
Looking towards the cutting shield at the hydraulic jacks.
Hydraulic jacks holding a TBM in place.
The support structures at the rear of a TBM. This machine was used to excavate the main tunnel of the Yucca Mountain nuclear waste repository in Nevada.
Tunnel boring machine at the site of Weinberg tunnell Altstetten-Zürich-Oerlikon near Zürich Oerlikon train station.
The first successful tunnelling shield was developed by Sir Marc Isambard Brunel to excavate the Thames Tunnel in 1825. However, this was only the invention of the shield concept and did not involve the construction of a complete tunnel boring machine, the digging still having to be accomplished by the then standard excavation methods.
The very first boring machine ever reported to have been built was Henri-Joseph Maus' Mountain Slicer. Commissioned by the King of Sardinia in 1845 to dig the Fréjus Rail Tunnel between France and Italy through the Alps, Maus had it built in 1846 in an arms factory near Turin. It basically consisted of more than 100 percussion drills mounted in the front of a locomotive-sized machine, mechanically power-driven from the entrance of the tunnel. Unfortunately, the Revolutions of 1848 irremediably affected the funding of the project and the tunnel was not completed until 10 years later, by using also innovative but rather less expensive methods such as pneumatic drills.[1].
In the United States, the first boring machine to have been built was used in 1853 during the construction of the Hoosac Tunnel. Made of cast iron, it was known as Wilson's Patented Stone-Cutting Machine, after its inventor Charles Wilson. It drilled 10 feet into the rock before breaking down. The tunnel was eventually completed more than 20 years later, and as with the Fréjus Rail Tunnel, by using less ambitious methods.
In the early 1950s, F.K. Mitry won a dam diversion contract for the Oahe Dam in Pierre, South Dakota, and consulted with James S. Robbins to dig through what was the most difficult shale to excavate at that time, the Pierre Shale. Robbins built a machine that was able to cut 160 feet in 24 hours in the shale, which was ten times faster than any other digging speed at that time.
The breakthrough that made tunnel boring machines efficient and reliable was the invention of the rotating head, conceptually based on the same principle as the percussion drill head of the Mountain Slicer of Henri-Joseph Maus, but improving its efficiency by reducing the number of grinding elements while making them to spin as a whole against the soil front. Initially, Robbins' tunnel boring machine used strong spikes rotating in a circular motion to dig out of the excavation front, but he quickly discovered that these spikes, no matter how strong they were, had to be changed frequently as they broke or tore off. By replacing these grinding spikes with longer lasting cutting wheels this problem was significantly reduced. Since then, all successful modern tunnel boring machines have rotating grinding heads with cutting wheels.
[edit] Description
A tunnel boring machine (TBM) typically consists of one or two shields (large metal cylinders) and trailing support mechanisms. At the front end of the shield is a rotating cutting wheel. Behind the cutting wheel is a chamber where, depending on the type of the TBM, the excavated soil is either mixed with slurry (so-called slurry TBM) or left as is. The choice of TBM type depends on the soil conditions. Systems for removal of the soil (or the soil mixed with slurry) are also present.
Behind the chamber there is a set of hydraulic jacks supported by the finished part of the tunnel which push the TBM forward. The action here is much like an earthworm. The rear section of the TBM is braced against the tunnel walls and used to push the TBM head forward. At maximum extension the TBM head is then braced against the tunnel walls and the TBM rear is dragged forward.
Behind the shield, inside the finished part of the tunnel, several support mechanisms which are part of the TBM are located: dirt removal, slurry pipelines if applicable, control rooms, and rails for transport of the precast segments. The cutting wheel will typically rotate at 1 to 10 rpm (depending on size and stratum), cutting the rock face into chips or excavating soil (muck). Depending on the type of TBM, the muck will fall onto a conveyor belt system and be carried out of the tunnel, or be mixed with slurry and pumped back to the tunnel entrance. Depending on rock strata and tunnel requirements, the tunnel may be cased, lined, or left unlined. This may be done by bringing in precast concrete sections that are jacked into place as the TBM moves forward, by assembling concrete forms, or in some hard rock strata, leaving the tunnel unlined and relying on the surrounding rock to handle and distribute the load.
While the use of a TBM relieves the need for large numbers of workers at increased pressure, a caisson system is sometimes formed at the cutting head.[2][3] Workers entering this space for inspection, maintenance and repair need to be medically cleared as "fit to dive" and trained in the operation of the locks.[2][3]
[edit] Shields
Modern TBMs typically have an integrated shield. The choice of a single or double shielded TBM depends on the type of rock strata and the excavation speed required.
Double shielded TBMs are normally used in unstable rock strata, or where a high rate of advancement is required. Single shielded TBMs, which are less expensive, are more suitable to hard rock strata.
[edit] Urban tunnelling and near surface tunnelling
Urban tunnelling has the special challenge of requiring that the ground surface be undisturbed. This means that ground subsidence must be avoided. The normal method of doing this is to maintain the soil pressures during and after the tunnel construction. There is some difficulty in doing this, particularly in varied rock strata (e.g., boring through a region where the upper portion of the tunnel face is wet sand and the lower portion is hard rock).
TBMs with positive face control are used in such situations. There are three common types: Earth pressure balance (EPB), Bentonite slurry (BS), and compressed air (CA). The compressed air method is the oldest, but is falling out of favour due to the difficult working conditions it imposes. Both types (EPB and BS) are clearly preferred over open face methods in urban environments as they offer far superior ground control.
When tunnelling in urban environments other tunnels and deep foundations need to be addressed in the early planning stages. The project must accommodate measures to mitigate any detrimental effects to other infrastructure.
[edit] Manufacturers
- TERRATEC
- Akkerman Inc.
- Hitachi, Ltd.
- Kawasaki
- Okumura
- NFM Technologies
- Herrenknecht
- The Robbins Co.
- LOVAT Inc.
- Wirth
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