billy bishop airport pedestrian tunnel article - north american tunnelling journal october -...

7/22/2019 Billy Bishop Airport Pedestrian Tunnel Article - North American Tunnelling Journal October - November 2013

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ESAS SEMCHALLENGECONSTRUCTION OF

NEW YORKS

NORTHERN BLVD

CROSSING

Tunneling

Oct/Nov 2013

BUILDING BILLY BISHOP

TORONTO CITY AIRPORTS PASSENGERTUNNEL PROVIDES A CHALLENGE

SEE PAGE 8

NEW IRVINGTONCOMPLETESLAKE MEADS $12M

CHANGE ORDER AND

OTHER NEWS FROM

NORTH AMERICA

SEE PAGE 5 DETAILS ON PAGES 24-26

INVESTIGATINGSEATTLE SOILS

A LOOK AT THE SR 99

TUNNELS GROUND

INVESTIGATION AND

TESTING PROGRAM


2/6NORTH AMERICAN TUNNELING JOURNAL 3

contentScomment

Front cover:In March 2012, construction began on a unique 614ft (187m) longunderwater pedestrian tunnel that will form a link from Torontos mainlandto the island home of the Billy Bishop Toronto City Airport, in Ontario,Canada. The tunnel is an unusual project that has set new records for thearea. At 10m (32ft) wide and 8m (26ft) high, the Billy Bishop tunnel is by farthe largest to have been built in the regions Georgian Bay shale.

To facilitate this, seven 1.85m (6ft)interlocking horizontal drift tunnelswere excavated using Technicoremicrotunneling machines, andbackfilled with concrete, to create aprotective arch under whichexcavation could proceed.

The CA$82.5 million project isbeing delivered on behalf of theToronto Port Authority via a public-private-partnership (PPP) model.Concessionaire Forum EquityPartners comprises: PCL

Constructors (Design-Builder),Johnson Controls (Facility Manager),Technicore Underground (TunnelContractor); Arup (Lead Designer),ZAS (Architect), and Exp(Geotechnical Engineer).

Vital circlesThere is a daunting web site on the Internet

that displays the worlds population in realtime. As you watch, the sites homepage

rapidly clocks up the number of people that

have been born, and have died, that day as

well as providing a running population

growth figure. Stare at the screen for a few

minutes and it starts to become a bit overwhelming (the worlds

population has grown by 18,000 in the last hour and a half). Did you

know that in 1970 there were roughly half as many people in the world

as there are today? Population growth rates have begun to decline

slightly, but current predictions still indicate that the worlds cities will

need to accommodate more than six billion people by 2050 thats

almost the entire population of the world today.Behind China and India, the US is the third most populated country in

the world, and without a more positive attitude towards increased

infrastructure investment in combination with sustainable urban

planning and the increased use of underground space the nations cities

are almost certainly going to grind to a crumbling halt. Canada and

Mexico are faced with the same issues in their major cities. And all this

becomes particularly frightening food for thought when put in the

context of how much time it takes to bring a major infrastructure project

to fruition. Many of North Americas current underground infrastructure

projects have been in the planning for more than several decades.

As Goodfellow illustrates in this months Insider column (p18),

infrastructure investment creates virtuous circles of growth in our cities.Id take that one step further, and say that those circles are vital.

Amanda Foley

5 North American NewsProject, contract & company news

8 Characterizing Seattles SoilsSeveral years were spent on an extensiveexploration and testing program in order tocharacterize ground conditions for the SR 99Tunnel Project (Alaskan Way) alignment

16 Cutting Edge 2013The full program for this years Cutting EdgeConference on Megaprojects is revealed

18 The InsiderGoodfellow looks at the virtuous circle ofbenefits that can arise from long-terminvestment in public infrastructure

19 Building the Breakthrough to Billy BishopA series of interlocking horizontal tunneldrifts, backfilled with concrete, have beenused as pre-support to safely excavateToronto City Airports new passenger tunnel

24 ESAs SEM ChallengeThe short 125ft (38m) section of SEM tunnelunder the Northern Boulevard, in Queens,has the accolade of being one of the mosttechnically challenging elements of NewYorks massive East Side Access Project

Right: Site

investigation

under way in

Seattle for the

SR 99 Tunnel

Project (p8)

Below: SEM

excavation of

East Side Access

Northern BlvdCrossing, in

Queens, NY (p24)


3/6

STANDING AT THE ENTRANCE to thepartially-constructed Billy Bishop Toronto CityAirport tunnel in Toronto, you could almostimagine yourself to be staring into the remainsof a temple, built by some ancient civilisation.Above, a fluted arch formed by interlockingdrift tunnels filled with concrete and to either

side, walls of layered shale, looking like rowsof fine brickwork. When complete, this 614ft(187m) long tunnel will form a link from themainland to the island home of the BillyBishop Toronto City Airport. Though a tinyplayer on the world tunneling stage, this is anunusual project that has set new records forthis area and geology.

A job like this is very unique, says TonyDiMillo, CEO of Technicore Underground whois building the tunnel. It presented manychallenges from the engineering design to theactual construction. Lake Ontario is a mere 6m

(20ft) from the mainland shaft, and only 10m(33ft) above the top most drift. The shape ofthe main tunnel is very unique and complex.And all this construction is also adjacent toexisting structures which continually remainedin operation.

The reason for the tunnels unusualinterlocking-drift arch is that it mustcope with the Georgian Bay shalethrough which it passes. Excavate ahole in this layered shale, and the wallswill begin to move slowly in on you,due to the combined effect of the rock

being horizontally stressed due totectonic activity, and the fact that ittakes in water from the air over timeand swells (see box, page 21).

Though plenty of tunnels have beenexcavated through this shale, they haveall been relatively small in diameter,mostly watermains and sewage tunnelsof 4m (13ft) diameter or less. At 10m(32ft) wide and 8m (26ft) high, the BillyBishop tunnel is by far the largest everto be built in these ground conditions.

Theres a rule of thumb in Torontothat says you must either wait threemonths between excavating and lininga tunnel to allow for movement or youmust install a compressible layerbetween the rock and the lining. Thistunnel is significantly larger than

NORTH AMERICAN TUNNELING JOURNAL 19

TORONTO

Building the breakthrough

TO BILLY BISHOP

The Billy Bishop

Toronto City

Airport tunnel in

Toronto, Canada,

is just 187m

(614ft) long, but

has required

nine TBM drives

to build it.

Kristina Smith

recently caught

up with theprojects

participants to

find out why


4/6

anything thats been done locally, says JonHurt, Tunnel Practice Leader for Arup whodesigned the tunnel. No one knew how ruleof thumb would translate with the increase insize. The Geotechnical Baseline Report (GBR)

took a conservative view of the potentialswelling, predicting maximum movementsdue to swell of up to 200mm in the tunnels.

The arch solution for the Billy Bishop tunnel,though it has been used before, is unusual.Seven 1.85m (6ft) interlocking horizontal drifttunnels, excavated using mini TBMs andbackfilled with concrete, create an arch verymuch like a secant pile wall on its side. Theconditions which require this solution dontcome together very often, says Hurt.

The short length of the Billy Bishop tunnelmeant using a conventional TBM would havebeen far too expensive. An alternative solution

would have been to use SEM, using a series ofheadings and gradually building up to thefinal diameter. SEM would have worked well,although it would have required plenty ofadvanced grouting if water bearing featureswere encountered, says Hurt. More groundinvestigation would also have been needed,involving very long, horizontal boreholes tocheck whether any vertical joints crossed theline of the tunnel. Ultimately it was thecontractors decision in terms of the risk hewanted to take, says Hurt. The concern isthat if you hit some kind of fault or featurethat lets in water, in an SEM heading, youdont really have any fallback. You can probeand grout in advance to try and avoid this, butthe mini TBM solution was felt to be safer.

Of the three consortiums shortlisted for thedelivery and operation of the Billy Bishop

tunnel, only the winning one proposed thisdesign. Forum Infrastructure Partners wasthe only one to submit the unique tunnelconstruction method utilizing the overheadarch, says Toronto Port Authority Director of

Infrastructure, Planning and Environment, KenLundy. The arch prevents water egress andprovides an additional layer of stability.

A long time comingAnyone using the Billy Bishop airport todaymust take a ferry from the mainland. Thecrossing, though only 120m in width, is aninconvenience for the passengers who use theairport each year; 2.3 million of them in 2012.

Once the new tunnel is in operation in theFall of 2014, there will be no need to wait forthe ferry which has a capacity of 200 people,although it will continue to run for those who

prefer it, and to carry vehicles across. And theconstant flow of passengers through the

tunnel rather than four ferry loads per hour should mean less queuing at check-in.

The original plans for the airport, namedafter Canadian first world war flying heroWilliam Avery Billy Bishop, were drawn up in

the 1930s and included a tunnel to connect itto the mainland. Due to political changes andwrangling, the tunnel was not constructed.Since then, there have been various plans tocreate links either underground or by bridge,including a 2002 scheme to create a liftbridge, but none of these came to fruition.

Toronto Port Authority finally got thisscheme off the ground by procuring thetunnel using a deal fashioned on a publicprivate partnership (PPP) format. Everypassenger arriving at the airport pays a $20airport improvement fee and part of this willgo to pay back the CA$82.5 million

construction costs over a period of 20 years.The authority signed the deal with

0+000 0+010 0+020 0+030 0+040 0 +05 0 0 +0 60 0+070 0+080 0+090 0+100 0+110 0+120 0+130 0+140 0+150 0+160 0+170

0+180 0+186.06

80

75

70

65

60

55

50

45

80

75

70

65

60

55

50

451.000%

3.990%

TORONTO

20 NORTH AMERICAN TUNNELING JOURNAL

Figure 1: Longitudinal section of the Billy Bishop Airport Passenger Tunnel

Tunnel driftsfilled with concrete

1

23

45

67

Sleeves cast intoconcrete for City Mains

Tunnel lining

Travelators TravelatorsWalkway

Invert Slab

Figure 2: Section of the tunnel showing drift arch

Temporary support in one of

the drifts prior to backfilling

Artists impression of the Billy Bishop Airport Tunnel


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concessionaire Forum Equity Partners inNovember 2011. Members of the consortiumare PCL Constructors, Johnson Controls,Technicore Underground, Arup, architect ZASand geotechnical engineer Exp.

Passengers travelling to the airport willaccess the tunnel via elevators inside a pavilion

building on the mainland, travelling throughthe tunnel on moving walkways, two in eachdirection. At the other end, escalators housedinside an extension to the existing airportbuilding will take passengers to ground level.

For Hurt and his team, one of the biggestchallenges is achieving an airport standardenvironment inside the tunnel. That meansvery tight controls on temperature, humidity,ventilation and lighting, says Hurt. Some ofthe site layouts were very constrained: wecould not create lots of space for theventilation so we had to work hard to fit it inwith the help of a 3D BIM (building

information modelling) model.Construction began in April 2012, with

installation of the secant pile walls for the 33mlong x 13m wide x 35m deep (108ft x 43ft x115ft) mainland shaft, followed by itsexcavation. Every third pile is reinforced with asteel I-section, and the shaft is temporarilybraced at water level and permanentlyanchored into the shale, which starts 30ft (9m)below surface under a layer of sandy fill.

Piling for the island shaft began in June2012. At 30m (98ft) deep, 5m (16ft) higherthan its counterpart across the channel, which

means there is an upward gradient on thetunnel from mainland to island side, achievedwith a 1% grade for the first half of the tunneland then a 4% grade on the second half.

It is the mainland shaft that has presentedTechnicore with the most challenges on theproject to date, says Michael MacFarlane,Technicore Project Engineer. This is perhaps notsurprising when considering the shaftsposition, wedged up against the historic quaywall of Lake Ontarios Western Channel.South wall movement in the mainland shaft,the side adjacent to the lake, required anadditional row of walers and struts, says

MacFarlane. Movements of the quay wall andthe secant pile walls have been closelymonitored during the construction period.According to Andrew Cushing, Senior Engineerfor Arup, the top of the quay wall moved20mm (0.7in) towards the channel during pileinstallation and then back around 5mm(0.19in) during the excavation of the sandyoverburden, without suffering any damage.

Further complications for Technicore camedue to rock fractures in the mainland shaft.These allowed water to seep into the shaft,which in the winter months led to large chunksof ice forming.

The behavior of the shale in the shaft hasprovided useful information for the designteam. One of the big design challenges wasgathering enough information about theground within the confines of a design-and-

TORONTO

How to design in swelling shale

The Georgian Bay Formation, in which the Billy Bishop Airport Pedestrian Tunnel is

being constructed, is characteristic of the Greater Toronto Area. It is comprisedprimarily of low strength, horizontally-bedded shale with intermittent hardsandstone and limestone layers. The shale presents several challenges for the designand construction of a tunnel, beginning with how to model the behavior of theshale. In order to get the most cost-effective design, we developed a numericalmodel, which is less conservative than the traditionally used closed form solution.

The horizontal bedding of the Georgian Bay shale, combined with a high in-situhorizontal stress state, has been known to result in roof stability problems uponexcavation of the full tunnel profile. Consideration of this factor resulted in theselection of the rather novel temporary tunnel crown pre-support system involvingthe seven 1.85m (5ft) diameter horizontal secant drift bores (figure 2). Use of thispre-support procedure eliminated the need to install rock bolts within the crown ofthe tunnel, thereby reducing the risk of groundwater inflows.

The shale is also subject to time dependent deformation, or swelling, as a

consequence of the large stress relief that occurs upon excavation in combinationwith a differential gradient in salinity between the saline rock porewater andfreshwater from percolating groundwater or even humid air. The shale was formedin saline conditions. Osmotic and diffusive processes result in a decrease in thesalinity of the rock porewater achieved by an overall increase in the water content,resulting in volumetric expansion of the shale rock over time.

The development of this time-dependent swelling relative tothe time of installation of thepermanent lining has a directimpact on the long-termmoments and forces induced onthe lining. A series of laboratory

swelling tests on shale samples,along with in-situ rock stressmeasurements, were obtainedand used in the engineeringanalysis of the tunnel lining.

Initially, an analytical closed-form solution was used to evaluate the interactionbetween the swelling rock and the tunnel lining and quantify the final liningmoments and forces. Developed by Lo and Yuen (1981), this solution treats the rockas a viscoelastic material using the Kelvin-Voigt model.

However, closed-form solutions do not consider the effect of stresses caused bythe time-dependent swelling on the swelling potential of the shale rock. Nor dothey take into account other stresses present that have also been shown to impacton the amount of swelling that takes place. The closed form-solution also assumesthat the tunnel has a circular cross section, which the Billy Bishop does not. As a

result of these factors, the closed-form solutions for the final unlined rock swellingdisplacement and lining moments and forces are conservatively over-estimated.

To obtain a more realistic estimate of these values, a numerical module to accountfor swelling was developed by Itasca on behalf of Arup and implemented in theFLAC 2D finite difference program. The final lining design was based on numericalanalyses using FLAC 2D and UDEC software.

Measurements taken during construction are being used to validate the design.Construction monitoring consists of horizontal movement profiles of the tunnelshaft walls from inclinometer readings, along with tunnel movement measurementsobtained from optical survey of prism points, multi-point borehole extensometersinstalled horizontally in the tunnel sidewalls, and measurements of horizontalconvergence using a mechanical tape extensometer.

For tunnel design, the choice between using the numerical model or closed-form

solutions depends on the nature of the project, the completeness of the rockparameters available, the geological conditions, and the stage of design. It would beexpedient to use the closed-form solutions for preliminary design consideration andthe numerical method to examine the selected sections to finalize the design. Forunderground structures in highly swelling rocks, the numerical model could lead tosignificantly more cost-effective designs.

NORTH AMERICAN TUNNELING JOURNAL 21

Andrew Cushing, Senior Engineer, Arup


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TORONTO

22 NORTH AMERICAN TUNNELING JOURNAL

build program. Tests have to run for 100days so to take that into the design schedulewas hard, says Hurt.

Additional tests with geotechnicalconsultant Exp and the University of WestOntario measured the swelling potential ofthe ground and gave Arup a more defined

range of parameters. We came up with aflexible design that had elements of theobservational approach says Hurt. Thismeant we could monitor what happenedduring construction in terms of themovements and make adjustments to thereinforcement in the tunnel walls asconstruction went on.

The potentially huge movements referencedin the GBR have not materialized on site shaft walls have moved by tens of millimetresdue to the behavior of the shale rather thanhundreds, says Hurt, with movement nowslowing to the order of 1mm per month.

Tunnelling beginsTechnicore started excavation of the first ofthe drift tunnels in December 2012.Manufactured by Technicore at itsheadquarters in Newmarket, Ontario, the twomicrotunnel machines, named Chip and Dale,weigh in at 198,416 pounds (90 tonnes), are10m (36ft) long and cost CA$2 million each.

Its quite an investment to build them, butthey will always be busy, says DiMillo. Thosetwo machines have both dug other tunnelssince the drifts were completed. Theres a real

demand for small machines of that capacity.These are the smallest machines thatTechnicore, which specializes in small-diameter TBMs, would build. Able to operatein soft or hard ground or in EPB mode, theyare very versatile, says DiMillo. Operated byone person, the TBMs excavate using acombination of disc cutters and rippers ontheir heads. Spoil is transferred by screwconveyor to the tail can, with muck cars usedat Billy Bishop to transport it to the shaftwhere it was craned to the surface. The TBMspush themselves forward using a gripper canwith spikes that expand into the shale.

Technicore drilled primary tunnels first,every other one, followed by the secondary orinterlocking ones; the first broke through inFebruary 2013, with the final drift completedin April 2013. The design allowed for thesequence of construction to be varied,depending on what worked best for the

contractor. Technicore used sea-cans, orcontainers, to raise the TBMs up to the rightheight for launch for the higher drifts.

All the drifts had to be temporarilysupported. The shale in the drifts turned outto be of good quality, allowing the use ofplywood bolted to the tunnel crownsupported by circular steel ribs as protectionfor the workers. Once each drift was dug, ithad to be backfilled with around 500m3

(655yd3) of concrete. Technicore removed thesteel ribs before concreting, leaving the boltsand timber lagging in place.

Getting the concrete right for the backfilling

operations was a tough technical challengefor Technicore for several reasons. It had to bepumped uphill; be poured continuously toeliminate cold joints; and to achieve a strengthof 15MPa within 28 days, but not to reach sohigh a strength that the TBM could not cutthrough to create the interlocking drift. Thisrequired a special mix design to be able toflow that far and to stay liquid over theduration of the pour, says MacFarlane. Andthe challenge is to get that flowability withouthaving a high cement content that wouldmean high strength. It was a balancing act

between flowability and strength.Technicore worked with additive supplierBASF and sister company TecMix, whichsupplied the concrete, to perfect the concretedesign. A mobile concrete batching plant onsite produced concrete which was pumpeddown the shaft to a second pump situated atthe level of the drift tunnel. The longest pourtook 14 hours, the last one nine hours.

Three of the drift tunnels contain sleevescast into the concrete, which will house awater main and two sewer mains. This wasan innovation proposed during theprocurement process, says Hurt. As we had

these drifts as part of ourscheme, it was relativelyeasy to fit the pipes into thestructure. The solution hassaved the City of Toronto anestimated CA$10 millioncompared to using a longdirectional drill below thetunnel.

Once the arch of drifttunnels was in place, Chipand Dale then drilled twopilot tunnels to aid with thebreaking out the maintunnel. And between Julyand August 2013,Technicore took out a bigcentral cut, 7m (23ft) wideand 6m (20ft) high. That

was carried out under the protection of thearch canopy and needed very little in the wayof support, says Hurt.

During September and part of October,Technicore used a Dosco roadheader to takeoff the bulk of the rock from the sidewalls andthen a smaller roadheader to do the finetrimming. A hanging template helped get theprofile of the walls right. As the side wallsprogressed, Technicore installed 3.5m (11.5ft)long dowels and friction bolts, followed by50mm (1.9in) of shotcrete reinforced withpolypropylene fibres. The next step will be tocut out the invert followed by waterproofing,using PVC sheeting. Technicore will concretethe invert first, which will contain drainage

runs and electrical conduits. And then thearch will be cast in place.The original design set a 150 day gap

between the primary and secondary lining toallow the rock to swell. However, thatrequirement has been revised, saysMacFarlane: Since the swell has beenconsiderably less than anticipated, the elapseddays has been reduced to 120 and will befurther reduced to 90 days. However, toaccommodate the remaining potential swell,the amount of reinforcing has been increasedin the sidewalls compared with the 120 daysexposure for the 90 days pour.

Once the tunnel structure is complete, thefit-out will begin, and the buildings aboveeach shaft can start to take shape. Theoriginal plan had been to open the tunnel forpassengers by April 2014, but that date isnow expected to be early September.

Though only a short section of tunnel, thenumber of steps required in the constructionof the Billy Bishop Tunnel and the intensity ofwork employed has been immense.Technicore has been working 24 hours a day,through both the TBM and conventionalmining operations since December 2012.

One thing about unusual projects is thatthey can be very difficult to schedule. This issomething we have never done before, saysDiMillo. Would Technicore do anythingdifferently if it was starting over? DiMillo isemphatic: Not a thing.

One of the micro TBMs is retrieved

View of the mainland shaft and the sea wall

billy bishop airport pedestrian tunnel article - north american tunnelling journal october -...

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