50 Jurutera, July 2008

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the talk on ‘Permanent Works Shotcrete in Hong Kong tunnels’ was delivered

by David Salisbury, an associate Director of Ove arup & Partners, Hong Kong with 20 years’ experience in tunnel design and construction, on 19 October 2007 at the IeM lecture hall in Petaling Jaya at 5.30 p.m.

the past ten years has seen rapid advances in sprayed concrete technology for use in underground construction works. In Hong Kong, the recent development of a number of large underground infrastructure projects has led to increasingly imaginative uses of sprayed concrete technology and in particular its use for permanent works.

Spray concrete has made great advances in recent years and is increasingly used in permanent works. In fact, sprayed concrete is better than cast concrete in terms of strength and quality. Salisbury started the lecture by introducing the tunnelling activities in Hong Kong.

at present, there are over 380km of bored tunnels in Hong Kong, 59km in the next seven years and at least another 50km has been planned by 2015. traditionally tunnels are constructed in hard rock but there is an increasing demand for large diameter soft ground tunnelling.

the presentation started with the review of tunnelling case studies on several projects in Hong Kong where alternative and innovative proposals for using sprayed concrete in the permanent works have been adopted. these include:• onepassshaftlining;• cavernsinexcessof20mspan;• complexjunctionsandirregularshapes;• formed surface finishing to provide

smoothhydraulicflow;• fullyreinforcedshotcrete;• application of shotcrete directly onto

waterproofingmembranesand;• drainagereliningworks.

Both dry and wet mix spray concrete (shotcrete) are used in permanent shotcrete applications ini) Caverns and tunnelsii) Shafts andiii) Other applications

Dry Mix ShotcreteFigures 2 and 3 show the examples of dry mix shotcrete used in Hong Kong.

Wet Mix Shotcreteadvantages:• Higheroutput(30m3/hr)• Qualitycontrol• Pumpoverlongdistances• Lessrebound(5-10%)• Steel&polymerfibres• Moreadvancedequipment

• Advancedmixdesign• Anothermethodofconcrete

placement

Figures 4 and 5 show the application of wet mix shotcrete.

Mix DeSign Dry MixOPCement………….......................….480kg10mm aggregate..........................…...600kgCrushed rock.…….............................1200kg

Figure 1: Use of shotcrete in engineering

Figure 2: Use of dry mix shotcrete in slope protection

Figure 3: Use of dry mix shotcrete in tunnel in Hong Kong

talk on ‘permanent Works Shotcrete in Hong Kong tunnels’ ...........................................................................................................................................................................................................................................................................

By: Engr. Dr Ooi Teik Aun, FIEM., P.Eng.

Tunneling and Underground Space Technical Division

51 Jurutera, July 2008

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accelerator.……….......................…….15kgWater (added at nozzle)

high PerforMance Wet MixOPCement……….................………...400kgPFa…………………….................…….60kgSilica fume……………...................…...40kg 10mm aggregate…….................……450kgCrushed rock.……...................……..1230kgWater…………...……................….…200ltrsrB561 (Superplasticiser)…....................6ltrsSteelfibresRL45/35……..................…30kgFibermesh 150…………...................…0.9kg

PerManent Shotcrete aPPlicationScaverns • IslandWestTransferStation-EPD• PakShingKokTunnels–MTRC• DisneylandResortline–MTRC• QueenswaySubway–Swire/MTRC

Shafts• KaiTakTransferScheme–DSD

non-Standard tunnel Sections• Corners-KwaiChungCable Tunnel–CLP• CrossPassages–LokMaChau SpurLine–KCRC

other applications• Hydraulicprofiling-KaiTakTransfer

Scheme–DSD• ReliningofNullah-KaiTakTransfer

Scheme–DSD

caverns – island West transfer Stationenvironmental Protection Department (ePD)• WastetransferstationonHKIsland

located within a hillside waterfront cavern

• Excavationinrock• Primaryshotcreteandpermanent

rockdowels• Concreteliningonlyatportals• Engineer’sdesign175,000m3• ShotcreteFinaldesign30,000m3• HK$200millionsaving

caverns – Pak Shing Kok crossoverMtr tseung Kwan O extension• 6.1kmofrunningtunnels• Standardtunnelliningbymovingform• Unreinforcedcastin-situconcrete• Not suitable forCrossings, Junctions,

FanNiches.

caverns – Pak Shing Kok crossover• One24mwidecrossoverCavern• Seven12mwidefanniches• Fivebifurcations• Two‘T’junctions• Allpermanentshotcretelined

caverns – tai yam teng tunnel nichesMTRDisneylandResortLine• 3kmlongshuttleconnectiontothe

new Disney theme park• 850mlongtunnelsection,5.4m

internal diameter • twofannichecaverns• sixothernon-standardsections• Sheetandsprayedmembrane

caverns – Queensway Subway• 300mlongpedestriansubway• Linkingdeveloperspropertiesand

Mtr station• Cavernenlargementforescalator

connection• Excavatedinrockwithlowcover

below major road• 15mwidex33mlongrockcavern• Constantlyvaryingsection• Constantaccessrequired• Fullytanked• Sprayedmembrane(Masterseal345)• Steelandpolymerfibres• Primarysprayedconcrete• Gunitesmoothinglayer

Figures 4 & 5: Applications of Wet Mix Shotcrete

Figure 6: Queensway Subway

Tunneling and Underground Space Technical Division

52 Jurutera, July 2008

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• Reinforcedconcreteinvert• Maintunnelunreinforcedcastin-situ• Leaksdivertedtotemporary

invert drain• Mastersealsprayapplied• Severallayersused• Roughsubstrate• 5-6mmthick• Sprayedoversheetmembrane

at intersections• Constructionjointspreparedwith

waterbarandsealant(Masterflex900)• Finalinspectionforleaks• Permanentsprayedconcreteapplied

directly onto Masterseal

• 600mmthickappliedin2-3layers• Minimalrebound(<10%)• Surveycheckthenfinallayer,nofibres• Escalatoraditfullyreinforced

sprayed concrete

Figure 6 shows the completed subway at Queensway.

Shafts – Kai tak transfer Drainage SchemeDrainage Services Department• 1.9kmlongstormwatertransfer

tunnel• Sixshafts

• Fourshaftsbytheone-pass shotcrete method

• Circular:7.0-8.5mI.D.• Depth:Max.21.0m• ShotcreteOnePassTemporaryand

Permanent lining• FoamConcreteBackfillfor

tBM entry• R.C.BaseSlab&RoofSlab• Pipepilesinstalled• Excavate2.0m• Steelringbeaminstalled• Excavate2.0mandshotcrete

Primary layer 200mm x 1.5m• ShotcretePermanentlayer 100mm x 1.0m• FloatfinishPermanentlayer• Pipepilesinstalled• Excavate2.0m• Steelringbeaminstalled• Excavate2.0mandshotcrete

primary layer 200mm x 1.5m• Shotcretepermanentlayer 100mm x 1.0m• FloatfinishPermanentlayer• EarlyStrength16MPaat

12 hours• Excavate1.5m• Fixhydrophilicandgrout

tube strips• Shotcreteprimarylayer 200mm x 1.5m• Shotcretepermanentlayer 100mm x 1.5m• Floatfinishpermanentlayer• Repeatthree-daycycle• Detailofshotcreteoverlapshowing

grout tube hydrophilic strips• Constructionjoint1.3mlong• Nomembrane,noleaks• Floatfinishasgoodascastin-situ

lining form

the talk on permanent work spray concrete was indeed very informative and it attracted some 90 participants.

Figure 7 shows a section of the participants in the IeM hall.

the talk ended at 7.30 p.m. with numerous interesting questions from the floor. Dr Ooi, on behalf of the tunnelling and underground Space technical Division presented Salisbury with a memento as a token of appreciation (see Figure 8). n

Figure 7

Figure 8

Tunneling and Underground Space Technical Division