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32

The picture, below, of the exaggerated long section of the Channel Tunnel was taken from Wikipedia. Full-sized image here. Some of the limiting factors for the Channel Tunnel are: Railways don't like steep gradients The tunnels comprising the Channel Tunnel were excavated using tunnel boring machines (TBMs). Like railways, they cannot tolerate steep ...


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The alignment of a tunnel constructed from two ends and meeting somewhere is the middle is achieved via old fashioned surveying methods. If the tunnel breaks through to the surface, surveying stations are accurately established on the surface of the Earth at each end of the tunnel. These days GPS surveying techniques would most likely be used for that. ...


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Tunnel Access To begin, to construct and use a tunnel, it needs to be accessed. Access will be via either a vertical or sub-vertical shaft or a ramp that wheeled vehicles can use. Shafts may be practical for mines, but for a traffic tunnel access via a shaft is impractical because of the rate of transfer of vehicles from one level to the other. A small ...


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I'm assuming you are asking about a tunnel between North America and Europe. There are two types of tunnel that "might" be possible: excavating a tunnel through the rock beneath the sea bed or sinking prefabricated sections of tunnel to the sea floor, joining them up and sealing them against water inflow. Problem #1 - Depth of the North Atlantic ...


6

Because with a flat head the waste material can be (relatively easily) collected and removed from the cutting face. With a cone-shaped bit that removal is not so easily accomplished. Cone-shaped bits tend to be used to push or compress the material out of the way, which is fine for "softer" materials ...


5

One of the main problem with tunnel boring machines is they are required for a specific tunneling job: a certain sewer tunnel, a one off underground rail tunnel, etc. Once the job has been completed the tunnel boring machine may no longer be required. In a particular location there may not a need to continually excavate tunnels. Tunnel boring machines aren't ...


4

Such measures do exist, but they don't always prevent careless drivers from ignoring the measures and crashing into low bridges. One bridge that I know of has been hit at least 100 times and has been hit many times since a safety gantry was installed in 2016 to prevent such crashes. This is a picture of the safety gantry that was installed. The the bottom ...


4

First is power those cutting lasers usually make relatively small cuts and take quite a bit of power and time. Scaling that up means waiting for a few decades to move a few meters if you can't get more power. Second is conservation of mass. All that rock has to go somewhere. If you use a laser it will evaporate. No-one wants to be breathing metal fumes in ...


2

I think your question actually might be missing a key difference between the two lining systems you mention. Your top image shows a segmental lining. This lining is constructed using the stop and start manner that you suggest. There are variations on a theme to this but for a typical segmental lining the machine boring the tunnel (TBM) pushes off the leading ...


2

At the risk of performing a pure lmgtfy, take a look at this page An interesting quote from that page: The operation was started in 1825 and was halted a number of times when the river burst in and flooded the workings. Isambard Brunel was put in charge of operations, and at one time nearly lost his life in a flood. In November 1827 Marc’s son, ...


2

With present technology dirt is one of the worst possible concrete additives. It brings the compressive strength of concrete down to unacceptable levels even at fractions of less than 2%. Elon Musk is one of the few people who has earned the license to say unbelievable things. If his team has come up with a paradigm changing concrete making method, many ...


2

Laterally circumnavigating problematic bedrock is not always possible or practical for the following reasons: This can increase the length and cost of the tunnel The problematic geologic zone may be too vast laterally Such an alignment may already be minimizing the impact of a problematic zone by targeting the best geological zone available. As to the ...


1

Tunnel linings come in a wide variety of materials and functions. Some are just finishing precast panels covering the tunnel structure which could be an elaborate system of tie-back wires, steel frames, shotcrete. Some are actually part of the structure, but generally not the waterproofing. Here is a link to the design concern guide. tunnel lining.


1

Mass produced? Depends what you mean by “mass” For the channel tunnel they made 5, 5 of such a specific machine is perhaps “mass”...


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It is possible to use granite instead of concrete in construction (remember that buildings were made out of stone long before concrete was invented), but only in those instances where the structure is guaranteed to never experience tensile stresses. By reinforcing the concrete with prestressed steel rods, it is possible to render the resulting structure ...


1

They have done their homework, one hopes. Many competent dense soils are basically self supporting, like all the caves. Yes there is compact or dens soil behind the cast iron panels to take advantage of soils structural strength. The cast iron is sufficient to take all the loads, even if it rarely is called in to take the full load. They have tested the ...


1

Regarding the word dirt. It depends on what a person means by dirt. Generally, it is understood that dirt means loose material such as soil or sand on or near the surface of the earth. In mining however, and this may apply to tunneling, the word dirt can sometimes be used used to describe the broken rock, or mined material, that is excavated from the mine ...


1

Surveying methods have been the norm for hundreds of years and work reasonably well. The use of laser positioning gives accuracies of around 1ppm or a millimeter per kilometer. There is also information obtained from the boring machines themselves (using inclinometers etc. ) to give additional accuracy. the skill of the surveyor is probably the limiting ...


1

It is not an easy answer... depends. Basically, depends on the length of the tunnel. For a short tunnel, let´s say 5 km, it is just a matter to create a grid on the surface, in top of the tunnel to give coordinates to both entries. Later on, the guide of the tunnel is made by total stations (theodolites anciently) by several methods: English traverse ...


1

In my experience groundworks refers to the site activity of shallow work in the ground, such as trenches (for foundations or drainage) and slab foundations. Tunnel construction comes under the term tunnelling. Tunnelling is a specialist activity: you wouldn't want a general groundworks contractor to try boring tunnels, and you wouldn't want a tunnelling ...


1

The most likely explanation for the waviness pattern is improper drilling and blasting practices leaving toe (the ridges) behind, particularly in the floor of the tunnel. In some case the ridging of the toe continues up the walls. It looks like the bottom row of blast holes (the lifters) weren't low enough & they weren't angled downwards. From the ...


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Barring other difficulties, it is unclear what advantages laser cutting would have in such an application. Lasers are useful in drilling/cutting of materials because of their high precision and ability to make very small cuts. Digging a tunnel is not a precision activity though. Even if a tunnel drilling machine were set up to use lasers, the cut ...


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