2012 appendix l tunneling operations

8/11/2019 2012 Appendix l Tunneling Operations

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CORRIBFIELDDEVELOPMENTPROJECT

OnshoreWorksConstructionofTunnel

METHODSTATEMENTRev02

TunnellingOperations


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ShellExplorationandProductionIrelandLtd. Title: TunnellingOperations

DraftEnvironmental ManagementPlan DocumentNo: COR14OP0000_SEPILEMP

MethodStatement Revision:02 Page1of6

SUMMARY

Thisdocumentdescribestheconstructionofthe4.9kmsegmentlinedtunnelinwhichtheCorribOnshore

PipelinebetweenGlenagdandAughoosewillbeinstalled.

PURPOSE A4.9kmsegment linedtunnelwillbeconstructedusingaTunnelBoringMachine

(TBM)betweenAughooseandGlengad.

LOCATION The segment lined tunnelwillbe constructed from the starting shaft located at

Aughoose (approx. Chainage 88.77). From there, the pipeline route traverses

(underneath)theGlenamoyBogComplexcSACandtheBlacksodBay/Broadhaven

pSPA at Sruwaddacon Bay in a northwesterly direction towards Glengad for

approximately 4.9km, where the reception shaft (Chainage 83.88) will be

constructedinthecSAC. Thetunnelwillbeconstructedwithaminimumdepthof

coverof5.5m.

TIMESCALE It isanticipatedthatthetunnellingprocesswilltakeapproximately15monthsto

complete(atanaverageof11m/day).

Thetunnellingconstructionwillbecarriedoutona24hoursaday/7daysaweek

basis.

Otherassociatedworks,suchasmaterialtransportandtunnelarisingsdisposalwill

beexecutedbetweenthehoursof07:00and19:00weekdaysand07:00and16:00

Saturday.

CONSTRUCTION

METHODOLOGY

Thescope

of

works

for

the

construction

of

the

segment

lined

tunnel

can

be

generallydividedintothefollowingworksteps:

Constructionofthe4.9kmtunnelincludingaccessramps,startingshaftand

receptionshaft;

Installation and testing of the 20 inch gas pipeline and services in the

tunnel;and

Groutingofthetunnelandreinstatementoftheshafts.

Furtherdetailsontheconstructionofthestartandreceptionshaftsareprovidedin

othermethodstatements.

Prior to the commencement of tunnelling, the Aughoose compound is

constructedandassociatedutilitysystems,e.g.anappropriatesurfacewater

management system, are made available. A separate method statement

describestheconstructionoftheAughoosecompound.

Plantandequipmentrequiredforthetunnelling,includingtheTBM,arethen

mobilisedtosite.

AllTBMassemblyandmaterialsupplywillbemanagedfromthestartingshaft

inAughoose.


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Plant

and

Equipment

Themainplantandequipmentrequiredforthetunnellingprocessinclude:

Gantrycrane;

GroutmortarSilos

Slurrytreatmentplant

Bentonitetanksandsilos

Freshwatertank

Waterstoragetanks

Filterpress

Powergenerationunits

Following the installation of all the required plant and the set up of the site

compoundandfunctiontestingthetunnellingprocesswillcommence.

Tunnelconstruction:

The tunnelwillbeconstructedusingaslurryshield tunnellingmethodwhich

involves the drilling/boring of the soil face using a TBM and then installing

precastconcretesegmentsastheTBMprogresses.

ThecuttingwheelatthefrontoftheTBMtunnelsintotheground. TheTBMis

controlledby

the

steering

cylinders

within

the

TBM

which

pushes

the

cutter

headinthedesireddirection.

Powerswitchboards,hydraulicandlogisticunitsareallinstalledneartheTBM

onanumberofbackuptrailers.Thesetrailers(typicallyof810mlength)are

interconnectedandpulledbytheTBMthroughthetunnel.

Concretesegmentsare transportedtothefrontof the tunnelonatrain that

runsontrackswithinthetunnelduringconstruction.Thesetracksareinstalled

inparalleltothetunnellingoperationononeoftheTBMbackuptrailers.

Thestacked

segments

are

transported

through

the

tunnel

to

the

tail

skin

by

a

supplysystemwithtraincarsandcranes. Anerectorunit locatedwithinthe

TBMisusedtopickupthesegmentsfromthetrainanditinstallsthesegments

into the designatedposition. Once installed they arebolted to the already

installedringandsegments.

Concrete segmentswhich are erected inside theback endof the tunnelling

machine(thetailskin)andassembledtoformacompletesegmentringwhich

isconnected,groutedandwheninpositionactsasthetunnellining.

Aftercompletionofonesegmentring,alljackingcylindersareextendedfora

furtheradvance

cycle.

By

using

this

method

of

tunnel

lining,

the

already

built

concretetunnelremainsstationaryandservesasanabutmentfortheadvance


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oftheTBM. Grout(annulusgrouting) is injected intotheovercutbehindthe

installed segment rings, which is created by the cutting wheel during

excavation.

Slurrylines

for

spoil

transport,

air

duct

for

ventilation,

pressurised

air

supply

andpower/communication cables are installed inside the tunnel to support

thedrillingprocess.

Drilling fluid consisting of a suspension of water and bentonite (bentonite

slurry) is used for lubrication and cooling of the cutting head, removal of

cuttingsandstabilisationofthecuttingface.

Bentoniteslurrysuspensionwillbepumpedthroughthefeedingpipeintothe

TBMworkingchamber. Itismixedwiththeexcavatedsoil/rockandpumped

back through the slurrydischargepipe to the separationplant atAughoose

Compound.The

soil

is

separated

and

the

recycled

bentonite

slurry

suspension

pumpedthroughthetunnelbackintotheTBMworkingchamber.

Theexcavatedmaterialsfromtunnelling(tunnelarisings)isseparatedfromthe

drilling fluid/bentoniteslurrymixtureusingaseparationplantwhereshakers

aredeployed and stockpiled temporarilywithin theAughooseCompound in

designatedarea.

Thesurplusbentoniteslurrywillberemovedanddewatered ina filterpress.

After being treated in the filter press the filter cake is dry enough for

transportation to a licensed waste facility. The Filter Press water will be

monitoredthen

recycled

/reused

on

site,

where

feasible,

or

transported

off

sitetoalicensedwatertreatmentfacility.

MixingofGroutMortar

Groutmortarwillbeusedforgroutingtheannulusofthetunnel(voidsbehind

the segments). The grout mortar will also be used for filling the tunnel

followingtheinstallationofthepipelineandservices.

Mixing of grout will take place in a controlled and contained environment

usingautomatedmixingtankslocatedintheAughooseCompound.Groutsilos,

locatedadjacent

to

the

mixing

tanks,

will

be

filled

with

dry

cement

brought

in

bycontainertruck.Thecementwillbeblown intothestoragesilosfromthe

container truck using a sealed unit and stored there formixing as required

duringtheworks.

The mixing operation will involve the grouting mix and water. This is then

pumped in containerswhich are transferred to the tunnel using the tunnel

railway.

Topreventingressofwaterandgrout intotheTBM,brushsealsbetweenthe

tailskinandtheerectedsegmentsarefilledwithgrease.


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Demobilisation

and

Reinstatement:

WhentheTBMreachesthereceivingshaftinGlengad,itwillberecoveredand

the installationof thegaspipeline and services can start. Installationof the

pipelineandservicesisfromAughoose.

DemobilisationoftheTBMwillbecarriedoutattheGlengadsite. Tunnelling

equipment, such as separationplant,bentonite treatmentplant, grout silos,

etc.attheAughooseCompoundwillbedemobilisedinstagesuponcompletion

ofthesignificantelementsoftheworks.

Oncetheonshorepipelineandassociatedserviceshavebeen installed inthe

tunnelandthetunnelfullygrouted,thestartshaftandrampwillbebackfilled.

Backfilling

of

the

Tunnel

&

Pipeline

Installation:

The grout mortar will also be used for filling the tunnel following the

installationofthepipelineandservices.

Theequipmentassociatedwiththisbackfillingoperationwillbelocatedatthe

Aughoosecompoundandthebackfillingoperationwillbecarriedoutfromone

sideonlybypumpingthebackfillingmixthroughthepreinstalledgrouting.

EQUIPMENTTunnelboringmachine(TBM) Filterpress

TBMbackupsystem Supplysystem,feedingpipes/cables

Tunnelsegments ControlStation

Trackandtrainsystem Liftingandloadingdevices

Separationplant Tanks

Bentonitehandlingunit Gantrycrane

Bentonite

silos

Mortar

silos

RESTRICTIONS Tunnelwillbeconstructedunderneath:

BlacksodBay/Broadhaven pSPA

GlenamoyBogComplexcSAC

Noiseandvibrationlimits

Lightingconstraints

NonessentialactivitiesmayrequiretobesuspendedattheAughooseCompound

on Easter Sundays during periods when Mass is taking place at the nearby

commemorativesite.


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POTENTIAL

ENVIRONMENTAL

IMPACT

MITIGATION

Release

of

bentonite

to

environment

Thecompositionofslurryisdesignedtosuitthegeotechnicalconditions.

Bentonitepressureandrateofusagewillbemonitoredconstantly. Inthe

eventofbentonitereleasethebentoniteoperatingpressurewillbereduced

immediatelytoreducebentoniteloss.

Bentonitesensorswillbeinstalledintheexcavationchamber. Thechamber

canbeseparatedfromtheslurrysystem.

TheTBMspeedwillbealteredtosuitthegroundconditions.

Intheunlikelyeventofabentonitereleasethedesignandoperationofthe

TBM

will

limit

the

volume

to

7m

3

.

Measureswill be implemented atAughoose andGlengad to prevent any

egressofbentonite intowatercourses leading intothecSAC/pSPA.Ahard

standingareaforbentonitehandlingplantwillbe located intheAughoose

Compound. There is a separate drainage system where the runoff is

collectedandpumpedintoausedbentonitetank.

During removalof theTBMatGlengad, theshaftwillbepartially flooded.

This water will be contained within the shaft and removed offsite for

treatment at an appropriate licensed water treatment facility. Robust

measureswillbe taken toensurethere isnobentonite releaseduring the

loading,handlingandtransportoftheTBMinGlengad.

Noise,vibrationand

lighting

disturbance.

Noise and vibration will be minimised through design, and appropriate

selectionofplantandequipment.

Proactivemaintenanceofmachinery.

Claddingofstationarymachinerysuchasgeneratorsandseparationplant.

Acousticscreening&fencing.

Siteand

mobile

lighting

will

be

designed

to

limit

light

spillage.


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POTENTIAL

ENVIRONMENTAL

IMPACT

MITIGATION

Disturbance

to

birds

in

the

adjacent

pSPA

and

birds

on

migration

Acoustic screening barriers will be installed on the temporary perimeter

palisadefencing.

Solidacousticfencingwillbeusedwithinthecompoundtominimisenoise.

Lighting will be designed to minimise light leakage into the pSPA (light

intensitynomorethan0.3luxattheshoreline).

Green (beacon) lightingwillbe installedon tall structuresanduprights to

reducecollisionrisk.

Settlementpondswillbecoveredbyasuitablebirddeterrentmaterial.

Robustsedimentandpollutioncontrolmeasurestopreventimpactonprey

speciesintheBay(benthicmacrofaunaandfishspecies).

See LVI, Glengad Compounds and Access RoadMS for details of further

mitigation.

Potentialforindirect

impact

on

habitats

and

species

in

the

adjacent

cSAC

/pSPA

Robustmeasures (see below andAughoose Compound ConstructionMS)

willbeimplementedtopreventsedimentationandpollutionoftheadjacent

Annex I estuarine and interidal habitats in Sruwaddacon Bay and species

whichdependuponthem,includingsalmon.

Pollution

of

Land/Water/cSACand

pSPA

habitats

&

species

due

spillage

or

leaks

of

oil/dieselfromplant

and

equipment.

Machineryandplantwillbeinspectedpriortomobilisationtosite.

Refuellingofplant/machinerywilltakeplaceindesignatedareasonly.

Spillkitswillbeavailableonsite.

Releaseofsuspended

solids

from

the

works

could

have

negative

impactonwaterquality

Asurfacewatermanagementsystemwillbeutilised toensure removalof

suspended solids prior to discharge to receiving waters at an agreed

location.

Pumpedwaterwillbesubjecttosedimentcontrolmeasures.

Earthworks

may

disturb

archaeologicalremains

A licensed archaeologistwill be on site tomonitor all excavations of the

tunnelstartandreceptionshafts.

Intheeventofanarchaeologicalfindthearchaeologistmayhaveworkon

thesite

stopped,

pending

adecision

as

to

how

best

to

deal

with

the

archaeology by the Department of Arts, Heritage and Gaeltacht Affairs

(DAHGA)(previouslyassignedtotheDepartmentofEnvironment,Heritage

andLocalGovernment(DoEHLG).

2012 appendix l tunneling operations

Documents