Terminology

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

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>		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 tunnelling. See drill and blast.

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>		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.

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>		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.

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>		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.

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>		Full face boring machine : A tunnelling 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)

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>		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-fabricated concrete modules, or reinforced construction with spread foundations. freezing or other methods.

>		Grouting : Unstable rock and soil is strengthened by the injection of chemicals, cementitous grout,

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>		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.

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

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>		Jacking : Construction of small diameter passages by forcing pipe through the soil.
		Also known as Pipejacking.

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>		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 initial 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.

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>		Micro tunnelling : Construction method for tunnels which are too small for humans to dig inside.
		May be performed using tethered, remote-controlled drilling machines or pipe jacking.

>		Muck : Debris removed during excavation.

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>		NATM (New Austrian Tunnelling 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.

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

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>		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.

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>		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.

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>		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 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.

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>		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 tunnelling machine which has cutting teeth at its front.
		It creates the tunnel opening while passing the waste material through the rear.

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>		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.

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>		Water table : 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.