Terminology

STRUCTURES: Tunnel

Axis
The lengthwise course of a tunnel, especially along the center line.

Bentonite
Clay formed from volcanic ash which can absorb large amounts of water and expands to many times its normal volume. Used to retain the sides of excavations in wet, unstable soil.

Bore
Construction method for tunnels which involves digging a tube-like passage through the earth. Usually refers to mountain tunneling. See drill and blast.

Caisson
A pressurized, bell-shaped structure which allows construction fully under the water. Compare with cofferdam.

Cofferdam
A waterproof wall, open at the top, enclosing a construction area below the water level. Compare with caisson.

Conduit
Pipe or liner used as a passage for other pipes or wires.

Course
In tunnels, the path of a tunnel. In masonry, one horizontal row of blocks.

Consolidation
Soil stabilization; see grouting.

Cross section
The shape of a tunnel; shapes include ovoid, horseshoe, round or square.

Cut and cover
Construction method which involves excavating a large trench, building a roof structure, then covering it with earth. Commonly used for subways and relatively flat locations.

Dewater
Removal of water during construction.

Diaphragm wall
Watertight wall formed from cast-in-place reinforced concrete. Commonly uses slurry wall construction.

Drift
A horizontal, underground passage.

Drill and blast
Construction method in which pilot holes are drilled for explosive charges. The resulting debris is carried out and the process is repeated.

Embedded wall
Retaining wall constructed using sections placed side-by-side or interlocking to form a continuous structure. Includes sheet pile, soldier pile, bored pile and diaphragm wall.

Excavation
The process of digging or the hole which results.

Full face boring machine
A tunneling machine which has cutting teeth at its front. It creates the tunnel opening while passing the waste material through the rear. Many types of tunnel boring cut small sections which are progressively enlarged. A full face boring machine cuts the complete cross section of the tunnel at once. See tunnel boring machine (TBM)

Grade
The elevation of the ground surface. Often used to describe the angle or slope of the surface.

Gravity wall
Retaining wall relying on significant mass, dimensions or modular sections. Little or no stability is gained from the natural resistance of the supported. soil. May be large stone blocks, pre-fab concrete modules, or reinforced construction with spread foundations.

Grouting
Unstable rock and soil is strengthened by the injection of chemicals, cementitous grout, freezing or other methods.

Immersed caisson
A pressurized, bell-shaped structure which allows construction fully under the water.

Immersed tube
Construction method using pre-fabricated tunnel sections. While the ends are sealed, it is lowered into position under the water and attached to other sections. Also sunken tube.

In-situ
Formed or created in its final position.

Initial support
Applied or installed immediately to the interior surface after excavation to maintain the opening. Includes shotcrete, rock bolts and/or steel ribs.

Jacking
Construction of small diameter passages by forcing pipe through the soil. Also Pipejacking.

Lagging
Boards placed side-by-side to retain the face of an excavation. Held in place by soldier piles.

Line
A description of the location and grade of a tunnel.

Lining
Materials used to finish the inside surface of the tunnel. The inital supports and preliminary liner are placed as the tunnel is being excavated. These help stabilize the interior surface. Shotcrete may be sprayed on as a preliminary liner. Later, additional coatings may be applied or other types may be used such as prefabricated steel or concrete panels, rock bolting, steel ribs and wood lagging, or masonry. Waterproofing liners are also used.

Longitudinal
Along the length of a structure.

Microtunneling
Construction method for tunnels which are too small for humans to dig inside. May be performed using tethered, remote-controlled drilling machines or pipejacking.

Muck
Debris removed during excavation.

NATM (New Austrian Tunneling Method)
Construction method, also known as the shotcrete method. As the excavation progresses, a layer of concrete is immediately sprayed on the interior surface of the tunnel and rock bolts are driven in. This method attempts to maintain the original rock structure by avoiding settling, subsidence and deformation. Additional liners may be added or more layers of shotcrete may be applied.

Overburden
The soil and rock supported by the roof of a tunnel.

Pipe roof method
Construction method in which steel pipes are laid along the sides and roof of the tunnel course and the tunnel was then constructed inside.

Portal
The open end of a tunnel. Usually includes a wall to retain the soil around the opening. May also include service and ventilation building.

Profile
A side view of the tunnel.

Reinforced soil wall
Retaining wall using various methods of attaching strips, mesh or other reinforcements to an excavated face. Soil nails may be driven in to attach the reinforcements and added further stability.

Rock bolts
Steel bar with larger plates at its head. These are driven into the interior surface of the tunnel to stabilize and add strength to the rock. See soil nails.

Shaft
A vertical, underground passage.

Sheet pile
Pre-fabricated sections installed vertically side-by-side to form a retaining wall.

Shield
A metal frame used to maintain the opening as the tunnel boring progresses. As forward progress is made, the liner is constructed behind the shield, and the the shield is jacked or moved forward.

Shotcrete
Quick-setting concrete is sprayed onto the bare rock surface immediately after excavation. It forms preliminary tunnel liner.

Slurry Wall
Construction method used in wet, unstable soil. As the trench is excavated, it is filled with bentonite slurry. This fluid mixture allows the excavation to continue while preventing the passage of groundwater or the collapse of the trench walls. The trench is later backfilled with other material, forms for poured concrete walls, or pre-fabricated wall sections.

Soil nail
Steel rod driven into the ground to stabilize soil. Used as part of a retaining wall and may be attached to reinforcing strips, mesh or other buried anchors (deadman). Also call a tieback.

Soldier pile
Steel H-shape beam driven vertically into the ground to provide supports for lagging.

Spile
Rod driven into soft ground or unstable rock to provide stabilization. A grouted spile is one which is inserted into a pre-drilled hole, when is then back-filled with grout.

Sunken tube
Construction method using pre-fabricated tunnel sections. While the ends are sealed, it is lowered into position under the water and attached to other sections. Also immersed tube.

Tailings
In mining, waste material remaining after the valuable minerals have been extracted. Stored in piles or used as fill.

Tunnel
An underground passage for vehicles or pedestrians, especially one which is created by digging into earth. Occasionally, tunnel structures are built in an excavated area then covered over.

Tunnel Boring Machine (TBM)
A tunneling machine which has cutting teeth at its front. It creates the tunnel opening while passing the waste material through the rear.

Vault
An enclosing structure formed by building a series of adjacent arches. A long passageway having a curved ceiling or roof.

Ventilation
Circulation of fresh area and exhaust gases.

Watertable
The underground elevation below which the earth is saturated with groundwater. Groundwater includes rainwater which has seeped below the surface or is supplied by aquifers, water-saturated layer of rock.




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Page created: 24-Feb-1999
Last modified: 5-Jan-2000

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