Appendix C Glossary of terms

Alignment control The ability to steer a TBM on the correct line, leveland route coordinates by using a laser guidance system and dieren-tial use of the main thrust rams, and/or the TBM articulation or itscutterhead articulation.

Annulus The space, gap or void left around the body of the TBM (theTBM annulus) by the slightly larger cut diameter of the TBM cutter-head, and around the rings of segmental lining, which are smalleragain in outside diameter.

Atterberg limits for clays The boundaries (determined by laboratorytests) of moisture content in a soil between the liquid state and plasticstate (known as the liquid limit); between the plastic state and the semi-solid state (known as the plastic limit); and the dierence between theliquid limit and the plastic limit (known as the plasticity index).

Boulders Pieces of hard material in a soft ground matrix of a mini-mum dimension greater than 20 cm.

Bulkhead The steel partition within the TBM shield that contains thepositive operating pressure within the excavation chamber or plenumand allows the remainder of the tunnel to be at normal atmosphericpressure. Through this bulkhead must pass, in pressure-tight seals,the drive unit of the rotating cutterhead, the outlet and intake ofthe slurry circulation system of an STM or the screw conveyor ofan EPBM, and the air locks that allow for man and materials entryinto and exit from the pressurised plenum.

Chainage The length of or distance along a tunnel as measured fromthe rst ring of permanent lining to the last ring built.

Copycutter A cutter that extends mechanically beyond the diameterof the cutterhead to create overcut when required.

Cutterhead The rotating head or wheel at the front of a TBM that cutsor excavates the tunnel face.

Cutters Tools on the cutterhead used to excavate the ground. Thesecan be either pick tools or disc cutters or a combination of both.

Data-logger The electronic memory device that accepts informationfrom instruments that record all the vital functions of the TBMand stores the data for future use as well as displaying vital operatinginformation via a computer and in real time on screens in theoperators cabin for use by the TBM operator. In addition the datacan be relayed via a telemetry link from the TBM control cabin tothe surface computer installation where the information can beread in real time as well as being used for diagnostic reviews of theTBM performance.

Drive The distance of the tunnel face or TBM from the point of start-ing to the point of its planned breakthrough.

Gas monitoring Sensitive detectors of natural gases installed at strategicpoints on a TBM that, when linked to the TBMs PLC control system,will automatically shut down the TBM and sound an alarm for thetunnel heading to be evacuated should they detect dangerous gasesabove pre-programmed trigger levels.

Gauge cutters Cutting picks or discs xed on the periphery of thecutterhead and set to cut beyond the diameter of the cutterhead toprovide clearance.

Closed-face tunnelling machines and ground stability. Thomas Telford, London, 2005 67

Geotechnical The use of scientic methods and engineering principlesto acquire, interpret and apply knowledge of earth materials forsolving engineering problems.

Grizzly bars Bars xed across the cutterhead openings to restrict thesize of lumps or boulders that can get into the plenum chamber more usually used on EPBM machines where there is no facilityfor a crusher and the size of lump or boulder is limited by thescrew size.

Ground monitoring The process of installing geotechnical instrumen-tation along the tunnel alignment by which to record ground para-meters during a tunnelling operation. These parameters wouldinclude ground movement, both vertical (settlement) and horizontal,and the status of the groundwater regime.

Heading The advance of the tunnel face or TBM through the groundfrom the point of launch towards the point of eventual breakthroughor the contractual end point if completing a blind heading.

Hydrostatic head The height of groundwater above the tunnel axisthat exerts pressure at tunnel horizon. Every additional 10m ofwater head equals another 1 bar of pressure above atmospheric.

Lips and steps Slight misalignment of segments during ring build thatcreate either steps back or lips forward of the correct or exactplacement.

Operating pressure The positive pressure maintained within theplenum to support the exposed surfaces of the advancing tunnelface and to control the inow of groundwater (known also as facepressure).

Overbreak Unintentional removal of ground outside the requiredtunnel excavation. Usually occurs when ground breaks away fromthe excavation surface.

Overcut Intentional excavation of ground outside the requireddiameter usually needed to assist steerage of the TBM and createdby using a copycutter or by a xed gauge cutter that continuallyexcavates outside the diameter of the cutterhead.

Particle size distribution curve A graphic illustration of the distribu-tion of grain sizes in granular ground containing cobbles, gravel,sand, silt and clay.

Plenum The pressurised excavation chamber ahead of the TBMsbulkhead in which the material excavated by the rotating cutterheadis accumulated for extraction into the atmospheric or free airenvironment either through the out-bound pipeline of an STM tothe treatment plant, or through the screw conveyor of an EPBMinto muck haulage skips or onto long conveyors.

Pressure cells Sensors installed on the bulkhead of the plenum ofclosed-face TBMs that gauge and indicate, to the TBM operatoron the operating console, the uctuation of operating pressurewithin the plenum.

Ring Assembly of the prefabricated segments that create each newround or advance of the tunnel. Each ring comprises a prescribednumber of segments to suit the tunnel diameter and can be up to2m wide or more. Segments are usually made of precast concretebut can also be made of cast iron.

Rock head Interface between bedrock and overlying alluvial depositsand top-soils.

Screw conveyor A large diameter Archimedean screw attached to theTBM bulkhead in an EPBM that allows for controlled removal ofexcavated material under pressure from the plenum and dischargesto free air at the discharge gate.

68 Closed-face tunnelling machines and ground stability. Thomas Telford, London, 2005

Segment erector The device within the TBM shield by which thesegments or plates of each new ring of tunnel lining are lifted intoposition.

Settlement Vertical ground movement above a tunnel that results in asettlement trough or depression at the surface.

Shove The length of one round of tunnel excavation or one stroke ofthe TBMs forward thrust rams against the last installed ring ofsegmental lining and before the next ring of segments is installed.

Soil Undisturbed ground ahead of and around a tunnel excavationoperation.

Spoil Excavated soil.Spoil conditioning Materials such as surfactant foam, bentonite, wateror polymers that are added to the spoil within the plenum to improveits viscosity and ow properties.

Tailseal The grease-fed wire brush seal in the tail of the TBM thatseals the gap between the tailskin and the extrados of the liningrings of segments. Usually consists of two, three or four rows ofwire brushes plus an emergency seal if included.

Tapered trapezoidal rings A particular design of segmental liningwhere every segment within a ring is trapezoidal in shape and ofthe same size. In addition the width of the segments around eachring varies or is tapered. This tapering allows rings of lining to bebuilt to accommodate horizontal and vertical curves by rotatingeach successive ring to create a longer chord on the outside of thecurve than on the inside of the curve and to ensure that the ringsremain in contact without the need for packing.

TBM annulus The space left around the slightly smaller-diameterTBM body by the slightly larger TBM cutterhead needed for steeringthe machine.

TBM articulation The articulation of the TBM shielded body. Thiscan be either active or passive articulation. Typically, active articula-tion is ram-assisted articulation of the front part of the shield. Passivearticulation is usually articulation of the tailskin and is controlled bythe passive use of rams.

Third party Independent property owners or vested interest groupswithin the zone of inuence of a proposed tunnel alignment or thoselikely to be impacted by the planned tunnel construction activity.

Tracking of a conveyor The ability of a conveyor to be adjusted inorder that the belt runs (tracks) centrally.

Transfer and continuous conveyor belts Used only with EPBMs toeither transfer excavated material from the EPB screw conveyor tothe point of being loaded into muck haulage skips or onto a con-tinuous conveyor attached to the wall of the advancing tunnel fortransportation back to the tunnel portal and deposited onto thesites muck stockpile before onward haulage to the nal disposal site.

Closed-face tunnelling machines and ground stability. Thomas Telford, London, 2005 69

Alignment controlAnnulusAtterberg limits for claysBouldersBulkheadChainageCopycutterCutterheadCuttersData-loggerDriveGas monitoringGauge cuttersGeotechnicalGrizzly barsGround monitoringHeadingHydrostatic headLips and stepsOperating pressureOverbreakOvercutParticle size distribution curvePlenumPressure cellsRingRock headScrew conveyorSegment erectorSettlementShoveSoilSpoilSpoil conditioningTailsealTapered trapezoidal ringsTBM annulusTBM articulationThird partyTracking of a conveyorTransfer and continuous conveyor belts