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Tunnel:
A Tunnel is an Underground or Underwater passage that is Primarily Horizontal. Relatively small diameter ones carry utility lines or function as pipelines. Tunnels that transport people by rail or by automobile often comprise two or three large, parallel passages for opposite-direction traffic, service vehicles, and emergency exit routes.
Raw Material:
Material used in Tunnels vary with the Design and Construction methods chosen for each project. Grout used to Stabilize Soil or fill voids behind the Tunnel lining may contain various Material, including sodium silicate, lime, silica fume, cement, and bentonite. Bentonite and water Slurry is also used as a Suspension and Transportation medium for Muck and as a Lubricant for Objects being pushed through the Tunnel.
Water is used to control:
Dust During Drilling and after Blasting, which is often done with a low freezing Gelatine explosive. Water and salt brine or liquid nitrogen are common refrigerants for stabilizing soft ground by freezing. The most common modern lining material, concrete reinforced by either Steel or fiber, may be sprayed on, cast in place, or prefabricated in panels.
Choice of method:
A Tunnel construction method is Determined by several Factors, including Geology, cost, and Potential disruption of other activities. Different methods may be used on Individual Tunnels that are part of the same larger project.
The Manufacturing Process :
Preparing:
Site Geology is evaluated by examining Surface features and Subsurface core samples. A Pilot Tunnel about one third the diameter of the planned main Tunnel may be constructed along the entire route to further evaluate the geology and to test the selected construction method.
The pilot Tunnel:
may run alongside the main Tunnel path and eventually be connected to it at intervals to provide ventilation, service access, and an escape route. Or the pilot Tunnel may be enlarged to produce the main Tunnel.
Soil Stabilization is Required:
It may be done by injecting grout through small Pipes placed in the ground at intervals. Refrigerant may be circulated through Pipes embedded in the ground to freeze the soil.
Mining:
There are seven different methods used to remove material from the Tunnel path. The first is the Immersed Tube Method. Workers prepare an underwater Tunnel site by Digging a trench at the bottom of the waterway. Steel or reinforced concrete Sections of Tunnel shell are constructed on dry Land.
Each Section may be several hundred feet long:
The ends of the Section are sealed, and the Section is floated to the Tunnel site. The Section is tied to anchors adjacent to the trench, and ballast tanks built into the Section are flooded.
As the Section Sinks:
it is guided into place in the trench. The Section is connected to the adjoining, previously placed Section, and the plates sealing that end of each Section are removed. A rubber seal between the two Sections ensures a watertight connection.
Usually necessary to Stabilize and Reinforce the surface:
of the newly blasted Section with a preliminary lining. One technique involves inserting a series of Steel ribs connected by wood or Steel braces. Another technique, called the new Austrian Tunneling method (NATM), involves spraying the surface with a few inches of concrete.
Shield Tunneling:
This "shotcrete" lining may be supplemented by Inserting long Steel rods into the Rock and Tightening nuts against Steel plates Surrounding the head of each bolt. Tunnel Jacking is a Similar Technique, but the shield being driven through the ground is actually a prefabricated Section of Tunnel lining.
Micro Tunneling Machinery:
In the parallel drift method a series of Parallel, Horizontal Holes (drifts) are bored using micro Tunneling machinery micro Tunnels are too small for human miners to work inside of such as augers or small versions of TMBs.
These drifts are filled:
for example, Steel Pipes may be driven into them and then the Pipes packed with grout. The filled drifts form a protective arch around the Tunnel path. Excavation machinery is used to remove the soil from inside the arch.
Final lining:
In some cases, the final lining is placed during the excavation process. Two examples are TBMs that install lining segments and Prefabricated Tunnels that are jacked into place. In other cases, a Final Lining must be Constructed after the Entire Tunnel is Excavated. One option is to pour a Reinforced Concrete Lining in Place.
Slipforming is an efficient Technique:
in which a Section of form is slowly moved forward as the Concrete is Poured between it and the Tunnel wall; the concrete hardens quickly enough to support itself by the time the form moves on.
Byproducts/Waste:
Sometimes the earth removed from a Tunnel is simply discarded into a Landfill. In other cases, however, it becomes raw material for other projects. It may be used to form the base course for an approach roadway or to create roadway embankments for wider shoulders or erosion control.
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