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Tunnel Boring Machine

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(Redirected from Double shield TBM)
Construction Equipment
Tunnel Boring Machine
A tunnel boring machine (TBM) is used to dig tunnels in anything from hard rock to sand and anything in between, producing a smooth tunnel wall. The machine consists of several rotating cutting wheels on a large shield, which ranges in size from three to 60 feet (0.9 to 18 m).

There are both one and two shield models, each designed for boring different materials. Single shield models are ideal for hard rock strata, whereas double shielded models are generally used for less stable rock strata.

Contents

[edit] History

[edit] One Failure After the Next

The first tunnel boring machine was constructed by a Belgian engineer named Henri-Joseph Maus. The King of Sardinia approved the construction of a railway connecting France and Italy, and a tunnel was essential for its completion. Maus, who had already achieved an international reputation in mining, accepted the challenge to bore straight through Mt. Frejus.

Up until this point, tunneling was achieved by drilling a series of individual holes, filling them with gunpowder, lighting a fuse, hiding from the explosion, then quickly running back to brace the new hole before it collapsed. While this system did work, it was dangerous and inefficient.

Maus designed a large, complex machine with over one hundred percussion drills all set in a forest of cams, shafts, gears and springs. His tunnel boring machine was called the “Mountain Slicer,” and was built in a factory near Turin, Italy in 1846. While it had yet to prove itself, its sheer size alone attracted significant attention from tourists, many of whom viewed it “more as a piece of art than a tool.”[1]

The Mountain Slicer was not without its faults. It required an enormous amount of power to be successful, with all the energy provided by a source outside of the tunnel. As the machine moved further into the tunnel it required extension linkages and “the more linkages, the more power would be lost to transmission inefficiencies.”[2]

However, political “convulsions” of 1848 put a stop to funding Maus’ tunneling, so his machine was never tested to its full potential. The tunnel was eventually finished ten years later, but it was completed with drill and blast.

Many other inventors attempted to construct a tunnel boring machine, with little success. In 1851 a company from Boston, Richard Munn & Co., built a machine to help tunneling through Hoosac Mountain in northwestern Massachusetts. However, it jammed after just 10 feet (3 m). So, another engineer, Herman Haupt, decided to take over the project and develop his own machine, which died before it penetrated even one foot (0.3 m).

This lack of success continued with many other inventors and machines, one just as unsuccessful as the next. Most of these machines were based on the concept of “taking a rock drill and scaling it up.”[3] However, any drill large enough to bore a tunnel required too much power.

By 1930 many engineers had given up on the technology, resulting in few, if any, patents being applied for. This continued for the next twenty years.

[edit] Building a Machine That Works

However, hope was not completely lost. A young graduate from the Michigan School of Mines, James Robbins, became essential to the development of the first successful tunnel boring machine. After graduating in 1930 he spent the next 15 years working in the mining industry in California and Alaska. He eventually set up as a consulting engineer for the coal industry in Illinois.

He was approached by a tunneling contractor name F.K. Mittry to develop a machine capable of boring through Pierre shale for a water diversion tunnel just outside of Pierre, South Dakota. Pierre shale was a fragile material considered quite dangerous to drill and blast, so it was a unique challenge for Robbins.

Robbins knew of a new coal cutting technique that could work in this situation.

“The idea was to push a group of metal fingers or picks, like the tines of a fork, into the coal face and then rotate the group, scoring deep circular cuts into the coal. Freely rotating ‘wedging wheels’ or ‘bursting wheels’ were suspended between the tines; these shattered the weakened mineral off the face. The head carrying this pick and wheel assembly would rotate once, then retract, the coal would be shoveled up, and the process would repeat.”[4]

Robbins’ machine was called “Mittry’s Mole.” It weighed 125 tons, was 90 feet (27 m) long and had a diameter of nearly 26 feet (7.8 m). However, unlike its predecessors it was actually successful, boring up to 160 feet (48 m) in 24 hours, which was 10 times faster than most contemporary drills. Its success led Mittry to order more Robbins’ models. However, they failed to perform as well when boring different materials.

After this failure Robbins decided to establish a company dedicated entirely to the development of tunnel boring machine advancements and manufacturing. One of James S. Robbins and Associates’ first products was used for a sewer in Toronto, Canada. Its drag picks were constantly breaking off and needing repairs causing a lot of time spent doing maintenance. Robbins decided to strip the machine of the picks and allow a series of cutter discs to do the work on their own instead. The machine instantly became more successful.

The discs took advantage of the rock’s weakness by applying compressive tension to their cracks forcing them to fall apart.

This new machine also introduced a type of clean up for the dig. It was equipped with an “ingenious system of buckets” that picked up broken away material, lifting it onto a conveyor belt delivering it to the rear for disposal.

However, despite the newfound success of the tunnel boring machine, most contractors continued with the drill and blast system. Tunnel boring machines were much too expensive, around $1 million, and when they broke down it would result in several lost days while waiting for a part or engineer to repair it.

James Robbins died in 1958, leaving his son Richard to run his company. Most contractors did not trust Richard’s inexperience and the company suffered for a number of years, so did the tunnel boring machine.

[edit] Investment in Technology

In the late 1960s the tunnel industry was presented with an enormous contract and opportunity. The city of Chicago required a massive tunnel to be dug, more than a hundred miles long. However, “no contractor was going to be allowed to bid on the project unless he brought a tunnel boring machine with him.”[5] This led to considerable investment into the advancement of tunnel boring technology.

Cutting rates grew from 600 feet (180 m) per month in the late 1960s and early 1970s to as much 4,000 feet (1,200 m) per month in 2004.

[edit] Features/How it Works

Most tunnel boring machines are specially designed for specific projects. Each model will have some technical differences, but much of the design will remain the same.

The following description is for a tunnel boring machine designed for use on hard rock.

The head of the tunnel boring machine presses against the rock at the sides. The cutting heads attack the face of the rock with a force of 26 tons, which chips the solid rock away.[6] The rock falls onto a series of bucket wheels that transports it to a conveyor belt behind the head, delivering it to the rear of the machine.

Meanwhile, securing the tunnel walls is carried out immediately behind the cutting head. Two independently maneuverable drills drill holes into the surrounding rock for anchors, up to 13 feet (3.9 m) in length. There is also a mesh-placing machine that travels over the anchor drill placing steel mesh to provide protection from falling rock. (The type of securing measure depends entirely upon the local geology of the site: steel anchors, steel mesh, caps, or arches.)

The machine moves forward by two grippers that press against the rock on both sides of the tunnel. Hydraulic pumps pull the machine forward with these grips. Each stroke of the gripper moves the cutting head forward 6.5 feet (1.95 m). The gripper then retracts and moves forward again, pressing against the wall for another stroke.

Nearly 200 feet (60 m) behind the cutting head, a robot finishes the secured walls.

The whole machine works “like a moving factory,” 1,300 feet (390 m) long.[7]

[edit] Common Manufacturers

[edit] References

  1. History of the Tunnel Boring Machine. Fred Hapgood. 2008-09-24.
  2. History of the Tunnel Boring Machine. Fred Hapgood. 2008-09-24.
  3. History of the Tunnel Boring Machine. Fred Hapgood. 2008-09-24.
  4. History of the Tunnel Boring Machine. Fred Hapgood. 2008-09-24.
  5. History of the Tunnel Boring Machine. Fred Hapgood. 2008-09-24.
  6. The Tunnel Boring Machine. Youtube.com. 2008-09-24.
  7. The Tunnel Boring Machine. Youtube.com. 2008-09-24.