how tunnels work

by:Gewinn     2019-09-01
We have looked at some of the general principles of tunnel construction and let\'s consider an ongoing tunnel project whose potential and problems continue to make headlines.
The central artery is a major highway system running through downtown Boston, and many believe that the project named after it is one of the most complex projects-and expensive --
Engineering feat in American history
\"Big Dig\" is actually a few different projects in a project, including a brand
New Bridge and several tunnels.
A key tunnel completed in 1995 is the Ted Williams Tunnel.
It sneaked under Boston Harbor and took Interstate 90 from South Boston to Logan Airport.
Another key tunnel lies below the Ford Point Strait, the narrow waters used by Britain long ago as a boat toll station.
Before we look at some of the techniques used in the construction of these large excavation tunnels, let\'s review why Boston officials decided to do civil engineering on such a large scale
The first is the project.
The biggest problem is the bad traffic in the city.
Some studies have shown that by 2010, Boston\'s peak time may last nearly 16 hours a day, with serious consequences for both business and residents\' quality of life.
Obviously, some measures must be taken to ease traffic congestion and make it easier for commuters to navigate the city.
In 1990, Congress allocated $0. 755 billion for large-scale highway improvement projects, and a year later, the Federal Highway Administration approved the push.
In 1991, with the construction of the Ted Williams Tunnel, the big excavation began.
This underwater tunnel was used. and-
Real tunnel technology used in many different tunnels around the world.
Because Boston Harbor is quite deep, engineers have adoptedand-cover method.
The steel pipe, 40 feet in diameter and 300 feet in length, was dragged to Boston after being manufactured by Baltimore workers.
There, the workers completed each pipe with a road stand, an Air shell
Handle access and utilities as well as complete lining.
Other laborers dug a ditch on the floor of the port.
They then float the tubes to the scene, fill them with water, and put them into the ditch.
Once anchored, the pump removes the water and the worker connects the pipe to the adjacent part.
Ted Williams Tunnel was officially launched in 1995--
One of the few aspects of the large excavation completed on time and within the proposed budget.
It is expected to carry about 2010 cars a day by 98,000.
Interstate 90 traveled a few miles west into another tunnel below South Boston.
Just before me. 90/I-
No. 93 interchange, the tunnel and 400-foot-
Wide water bodies that provide some of the biggest challenges of big excavation.
Engineers can\'t use the same steel.
They used the plumbing method in the Ted Williams Tunnel because there was not enough room under the bridges of Summer Street, Congress Street and Northern Avenue to float long steel sections.
Eventually, they decided to give up steel.
Pipe concept, and use with the concrete tunnel section, this is the first use of this technology in the United States.
The problem is to make concrete parts in a way that allows workers to be in place in the passage.
To solve the problem, workers first built a huge dry dock on the South Boston side of the Strait.
The dry dock is called the casting basin, 1,000 feet long, 300 feet wide and 60 feet deep. -
Large enough to build six concrete parts that make up the tunnel.
The longest of the six tunnels is 414 feet long and the widest is 174 feet wide.
About 27 feet high.
The heaviest weighs more than 50,000 tons.
The finished part is sealed to water at both ends.
The workers then flooded the basin so that they could float the parts out and put them on the ditches that were dredge at the bottom of the channel.
Unfortunately, another challenge prevented engineers from simply lowering the concrete part into the trench.
The challenge is the red-line subway tunnel of the Gulf Traffic authority in Massachusetts, which is under the trench.
If no action is taken to protect the weight of the mass concrete section, the old subway tunnel will be damaged.
As a result, the engineers decided to support the tunnel section with 110 pillars sunk into the base bed.
These pillars spread the weight of the tunnel, protecting the Red Line subway that continuously transports 1,000 passengers every day.
There are other tunnel innovations in big excavation.
For part of the tunnel running under the railway yard and under the bridge, the engineers settled on the tunnel --
A technique commonly used to install underground pipes. Tunnel-
The top is to press a huge concrete box out of the soil.
The top and bottom of the box support the soil while the soil in the box is removed.
Once empty, the hydraulic jack pushes the case to the concrete wall until the entire case slides 5 feet forward.
Then, the workers in the newly installed interval tube-created gap.
By repeating the process over and over again, engineers were able to advance the tunnel without disturbing the surface structure.
Today, 98% of the construction related to big excavation has been completed, and the cost is far more than $14 billion.
But the return of Boston commuters should be worth it.
The old elevated Central Artery, which had only six lanes, was designed to carry 75,000 vehicles a day.
The new underground highway has eight to ten lanes and will carry about 245,000 cars a day by 2010.
The result is a normal city rush hour that lasts for hours in the morning and evening.
To see a comparison of big excavation to other tunnel projects, see the table below.
Engineers will continue to build longer and larger tunnels as tools improve.
Recently, advanced imaging techniques have been able to scan the Earth\'s interior by calculating how sound waves travel through the ground.
This new tool provides an accurate snapshot of the underlying environment of the tunnel, showing the type of rock and soil, as well as geological anomalies such as faults and cracks.
While these technologies are expected to improve tunnel planning, advances in other technologies will accelerate excavation and ground support.
Next generation tunnel-
Boring machines can cut 1,600 tons of muck every hour.
Engineers are also experimenting with other rocks.
Using the high-cutting method
Pressure water jet, laser or ultrasonic.
Chemical engineers are working on a new type of concrete that is hardened faster because they use resin and other polymers instead of cement.
With new technologies and technologies, tunnels that seemed impossible even 10 years ago suddenly became viable.
One of the tunnels is the Transatlantic Tunnel connecting New York and London. The 3,100-mile-
The long tunnel will hold a magnetic one.
The floating train travels 5,000 miles an hour.
Estimated travel time is 54 minutes--
Nearly seven hours shorter than the average transatlantic flight time.
For more information about tunnels and related topics, please see the link on the next page.
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