niagara tunnel project - technical facts

12/ 10/ 12 NI AG ARA TUNNEL PRO JECT - Technical Fact s

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NIAGARA TUNNELPROJECT

TECHNICALFACTS

Last updated on November 21, 2012

http://www.strabag.com/



VOICES from the Niagara Tunnel - A Living History

(click link above for more information)

A special THANK YOU is extended to the following companies

STRABAG INC.

ONTARIO POWER GENERATION

THE ROBBINS COMPANY

BERMINGHAM FOUNDATION SOLUTIONS

http://www.niagarafrontier.com/VoicesSubmissions.html



HATCH MOTT MACDONALD

&

GEO-FOUNDATIONS

The Niagara Tunnel Project

The Diversion Tunnel

10.4 km (6.5 miles) long, 140 m (459 feet) beneath the City ofNiagara Falls from the Sir Adam Beck Generating Complex to awater intake complex above Niagara Falls.

The new tunnel will increase the power supply for owner OntarioPower Generation (OPG) by 150 MW or 1.6 billion kilowatt hoursper year, enough electricity for a city twice the size of NiagaraFalls, Ontario, and its population of 80,000. Annually, the 150MWgenerated by the new tunnel will be enough to supply a city of700,000 people.

Unfinished Tunnel Diameter - 14.44-m (47.5-ft) excavateddiameter

Finished Tunnel Diameter - 12.5 m (41.1 ft) concrete-lined tunnelwith a finished diameter



Greatest Depth of Tunnel - 140-m (459 ft)

Water Flow - 500 m3/s (17,657 cf/sec) diversion capacity. Thetunnel water flow rate will be 4 meters/second.

Interior Tunnel Finish includes: two layers of waterproofingmembrane under 600-mm (23.6 inches) thick, unreinforced pre-stressed concrete injection lining overtop

Dewatering station and surface runoff structure

five 130 meter (427 feet) emergency tunnel dewatering shaftsoutside diameter 900 mm (35.4 inches) - inside diameter 700 mm(27.5 inches)lined with 200 mm (8 inches) of concrete and grout

Outlet Works

300 meters (984 feet) long by 20-m (67 feet) deep outlet canalOutlet structure with downstream closure gate and surge shaft

Intake Works

Intake Grout Tunnel constructed underneath existing Gate #1 ofInternational Water Control Dam within Niagara River Deep intake channel excavation Demolition and replacement of upstream ice control wallConstruction of new shore approach wallGrout Tunnel Planned Total Length - 403 meters (1,322 feet)Grout Tunnel Actual Total Length - 298.3 meters (978.6 feet) longGrout Tunnel Height - 7 meters (23 feet)Grout Tunnel Width - 8 meters (26 feet) Grout Tunnel Gradient - 7.150%



The

Intake

Grout

Tunnel

is

the

entrance

portal

for

water

flowing

into

the

new

Niagara

Tunnel

after

its

completion.

As

the

Tunnel

Boring

Machine

(TBM)

concludes

boring

the

tunnel

it

will

ascend

to



the

surface

along

the

Grout

Tunnel.

In

a

simple

sense,

the

Grout

Tunnel

acts

as

the

glide

path

for

the

emerging

Tunnel

Boring

Machine

(TBM).

The

diagram

on

the

left

gives

the

realistic

perspective

of

the

size

of



the

Grout

Tunnel

in

comparison

to

the

TBM.

The

most

important

aspect

of

the

Grout

Tunnel

was

to

allow

a

360°

high

pressure

grout

injection

into

all

the

rock

cracks

and

crevices

to

form

a

26

meter

diameter



waterproof

curtain

to

protect

the

tunnel

from

flooding

from

the

river

above

as

the

TBM

surfaces.

The

Grout

Tunnel

was

built

using

the

drill

and

blast

method.

Four



large

3

meter

deep

expansion

holes

were

drilled

near

the

lower

middle

of

the

rock

face.

The

remainder

of

the

rock

face

had

3

meter

deep

blast

holes

drilled

approximately

every

80

centimeters

apart.

The

holes

with

the



exception

of

the

expansion

holes

were

packed

with

explosives

and

detonated

in

a

diamond

pattern

so

that

the

blast

would

expand

toward

the

expansion

holes

resulting

in

a

controlled

explosion.

Every

blast

would

expand

the

tunnel

another

3

meters.



The

blasting

was

restricted

to

day

time

hours

only

as

not

to

disturb

nearby

neighbourhoods.

Contract

Hatch Energy in association with Hatch Mott MacDonald, isproviding Owner’s Representative services to Ontario PowerGeneration for the construction of the $640M Niagara Tunnelfacility project. This includes preparation of design/build contractdocuments, design review, construction monitoring and contractadministration. The design/build project is for a 10.4-km, 14.44-mdiameter water diversion tunnel and associated intake and outletworks.

The project is a design/build project with a partnering approach. Anegotiated Geotechnical Baseline Report (GBR) was used toequitably share underground risks on the project.

PROJECT COST: C$985 million

After evaluation and negotiations, the contract was signed in mid-August 2005, with the start of construction in September of thatyear. Actual tunneling commenced a year later after procurement,



fabrication and erection of the tunnel boring machine (TBM) withinthe constructed outlet canal.

The contract was awarded to Strabag AG of Austria.

Tunnel Design

The tunnel is being constructed in two passes with rock dowels,steel ribs, mesh and shotcrete, followed by a polyolefinmembrane and unreinforced 600-mm thick cast-in-place concretelining. The lining will be prestressed to resist internal waterpressure using a high-pressure 'interface' grout applied betweenthe shotcrete and the final lining. The combination of themembrane and prestressed lining system will prevent water fromentering the rock and resultant swelling. Two layers of membraneare being applied to the shotcreted rock enabling the spacebetween the membranes to be vacuum tested after installation inorder to ensure membrane integrity. The membrane will alsoprotect the concrete lining from the aggressive groundwaterconditions found in the Queenston Formation.

Tunnel Boring Machine (TBM)

The project uses the world’s largest hard-rock tunnel boringmachine (TBM) by the Robbins Company

TBM type Robbins HP 471-316



Year of manufacture 2006

Overall Machine diameter (new cutters) 14.44 m (47.2 ft)

The tunnel-boring machine is 2,000 tons, cost more than $30million, is powered by 15 electric motors that generate 6,375horsepower, and is able to chew through rock at the rate of upto10 feet per hour.

Cutter-Face

Cutters Face Series (size) - 508 mm (20 in.)

Center Series (size) - 431.8 mm (17 in.)

Number of disc cutters - 85

Nominal recommended individual cutter load 35 t /cutter

Cutter-Head

Cutter-head drive Electric motors/safe sets, gear reducers

Cutter-head power - 6330 HP (15 °— 422 HP) Expandable to 16°— 422 HP

Cutter-head speed 0–5.0 rpm

Approximate torque (low speed) 0–2.4 rpm - 18,800 kNm

Approximate torque (high speed) 5 rpm - 9,025 kNm

Thrust cylinder boring stroke - 1,729 mm (68 in.)

Hydraulic system - 300 HP (225 kW)

System operating pressure at maximum - 275.7 bar (4,000 psi) -recommended cutter-head thrust

Maximum system pressure - 310 bar (4,500 psi)



The machine has a cutter head thrust of 18,462 kN (4,150,422lbs) and a maximum torque of 18,670,000 N-m (13,770,285 lb-ft).

Electrical System

Motor circuit 690 VAC 3-phase, 60 Hz

Lighting system/control system 120V/24 VDC

Transformer size 4°— 1,700 kVA + 1°— 1,000 kVA

Primary voltage 13,800 V 60 Hz

Machine conveyor

Width 1,370 mm (54 in.)

TBM Weight (approximate) 1,100 metric tonnes, excludingdrilling equipment

For this construction, Strabag purchased a new Robbins HP mainbeam TBM, and a new HP backup system provided by RowaTunnel Logistics of Wangen,Switzerland.

The TBM Model 471-316, nicknamed Big Becky, is the world’slargest hard-rock TBM ever manufactured. Design of the HPmachine includes the use of 508-mm (20-in.) rear-mountedcutters, high cutter-head power and state-of-the-art groundsupport equipment

The cutter-head design for this project consists of a six-piecebolted and doweled hard-rock configuration that includes 12 muckbuckets with radial face and gage openings. Grill bars, abrasionresistant carbide buttons and abrasion resistant boltable bucketteeth are provided along the bucket openings. An abrasion-resistant faceplate and gage plates along with periphery grill bars



have been provided on the cutter-head structure. Foam nozzlesand rotary swivels have been provided to avoid problems if stickyground is encountered and to assist with the flow of the materialand avoid plugging of the buckets.

The finished weight of the cutter-head is more than 400 tonnes(440 st). The cutter-head is equipped with 85 cutter discs. Itincludes Robbins 508 mm (20 in.) wedge lock cutter assemblieswith a nominal thrust capacity of 35 tonnes (39 st)/cutter and anoperating capacity of 50 tonnes (55 st)/cutter. Overcut is providedby shimming of the outmost gage cutters should squeezingground be encountered.

Even though the Niagara geology is primarily soft rock, Strabagand Robbins agreed to provide the higher capacity cutters and508 mm (20 in.) rings to reduce the need for cutter changes. Inaddition, the 508 mm (20 in.) cutters and HP TBM configurationwill allow the use of the TBM on future hard-rock projects.



The Robbins Company TBM "Big Becky" Configuration



An example of the Gripper Type Tunnel Boring Machine (TBM)(this is not the same Niagara Tunnel Boring Machine)

TBM Assembly

To comply with the aggressive construction program outlined byOPG/Strabag, the supplied TBM system had to be designed,manufactured, assembled and made ready to bore within 12months after contract award. The project team achieved this bythe preassembly of the major critical components in a workshopand final assembly and commissioning of the complete machineat the project site. By doing this, the workshop assembly wasdone at the jobsite using the operating personnel. Robbinssupplied experienced supervision and specialty labor, whileStrabag supplied the local labor. This practice of jobsite assemblyachieved a 12-month, ready-to-bore schedule, which savedapproximately four to five months on the TBM delivery schedule.In addition, there were project cost savings associated with laborand freight, as these operations only needed to be done once andnot multiple times as with a workshop.



Components for the machine – which weighs a whopping 1,900tonnes and cuts a swath 14.4 metres in diameter – came frommanufacturers all over the world, including Canada, the UnitedStates, the United Kingdom, Hungary, Slovakia, Sweden,Germany and Italy.

Ground support

The design concept of handling the ground support is to bring theprimary support into the tunnel and handling of the support on topof the TBM. This allows the invert to be clear, which allows freeaccess of equipment for cleanup of the invert area. Contractrequirements necessitated several different support systemsbased on the type of ground encountered. TBM and backupassembly in launch pit.

The rock so far encountered, up to 180 MPa UCS, has beenlargely competent with some minor broken ground. A speciallydesigned foam system has also helped increase the TBMperformance in sticky ground. The water spray normally applied tothe cutter-head has been temporarily replaced with the foamsystem to assist in the flow of the material through the cutter-head.Five openings in the cutter-head allow the foam to be plumbed in,where it mixes with water and air.

L-1 Area Rock Support

The L-1 area is located directly behind the TBM cutter-headsupport, which is approximately 4.1 m (13.5 ft) from the rock face.The installation equipment includes the following systems:

Ring Beam Erector

A rotary-type ring beam erector is provided, with provisions tohydraulically lift the ring beam or channel section into place and



hydraulically expand the steel sections against the bored rock.The ring erector is located directly behind the TBM cutter-headsupport. It allows placement of the ring beams under theprotection of the roof shield fingers. The erector control functionsare operated by a radio control system, allowing the operator themobility to move along the top or bottom work areas as the ring isbeing erected. Design and operation of the steel erector allowsinstallation of the ring beams or channel sections during themining stroke.

Wire Mesh Erector/Material Handling Cart

A dual function handling cart, known as the donkey, is located onthe top section of the TBM main beam. The donkey transports thesteel sections and wire mesh forward into the L-1 working area.Supply of the donkey includes a hydraulic lifting device to handlethe wire mesh and steel sections to the crown where they canthen be installed. Operation of the unit is by radio control and isindependent of the boring stroke of the TBM.

Rock Drills

Two Atlas Copcp 6.4-m- (21-ft-) long BMH 6000 series hydraulicdrills with powerful COP 1532 hydraulic hammers were installed.The drills are installed on a rotary position locator, which allowsindependent operation of each drill. The position locator allowsthe various drill positions to be achieved to install the 6-m- (20-ft-)long rock bolts as per project requirements. Design of the systemallows the bolts to be installed during the boring operation.

Work Platforms

To assist the tunnel operating personnel in the installation of therock support, there are various stationary and mobile workplatforms located in the L-1 area. These platforms allow rockscaling, wire mesh and other ground support functions to beperformed.



Shotcrete Robot

Should shotcrete be needed in the L-1 area, a shotcrete robot hasbeen installed and integrated into the work platforms. The robothas been supplied by Rowa (Wangen, Switzerland)/Meyco-BASF(Switzerland, TX). It includes a boom to allow shotcrete coverageover a 180° section of the tunnel crown and at a rate of 15 m3 /h(530 cu ft/hour).

Shotcrete is being used throughout the drive as the primarymeans of tunnel support. Rubber-tired tractors transport shotcretefrom the onsite batching plant to two shotcrete robots located onthe back-up system. Each robot has 360-degree coverage andcan travel up to 8m in the longitudinal direction to spray shotcreteat the rate of 20m per hour. Additional types of rock supportinclude ring beams, wire mesh, and rock bolts.

Modifications

Other major changes to the TBM L1 area became necessary toreach the caved areas, including the addition of two hydraulic manbaskets and special drill rigs, mesh and anchors. These changeswere made incrementally as TBM progress allowed it. With thenew method, the over-break could be limited to 0.5m - 1 m (1.6 -3 ft), though the excavation process slowed to a maximum 5 m/d(16 ft/day).

L-2 Area Rock Support

Rock Drills

To complement the forward L-1 drills, two additional 6.4-m- (21-ft-) long BMH 6000 series hydraulic drills were installed on a rotarydrill positioner to allow installation of 6 m (20 ft) long bolts.



Shotcrete Robots

Two remote controlled shotcrete robots were installed in the L-2area. The units consist of a Meco-BASF spray head attachment,which allows 360° coverage. Each unit is independently controlledand has the ability to travel 6 m (20 ft) in the longitudal direction.The robots are charged by two Meco-BASF shotcrete pumps thatdeliver the shotcrete at a rate of 15 m3/hour (530 cu ft/hour) perpump.

Muck Haulage

Muck haulage is achieved by the use of a continuous conveyorsystem. As the backup is advanced, sections of conveyor areinstalled to allow continuous operation of the system. Muck istransported to the portal on the continuous conveyor where it isthen discharged to an overland conveyor and to the storage arealocated adjacent to the jobsite.

includes a 105 m (345 ft) long back-up system, which willtransport 1.7 million m3 (2.2 million cubic yards) of rock debris viaconveyor belt.

Air Compressors

two CompAir L160 compressors

The boring machine rides on the front of a sledge, which tunnelsthrough the rock at a speed of up to 15 metres per day, creating a14.4 metre diameter ‘hole’ that must be lined and reinforcedrapidly to prevent the tunnel collapsing behind it. A critical safetycomponent The compressors are a critical component in thisoperation, as they provide a totally dependable source ofcompressed air, 24 hours a day, which is used to propel theinjection concrete to form the inner wall of the tunnel. For Strabagtherefore, choosing the right compressor supplier was vital to boththe project’s on-time completion and the safety of the contractorsworking in the tunnel. CompAir technical representative, BobPaton explains. “Strabag was very keen to use our compressors



from the outset. Its own engineers and the manufacturers of thedrilling machine had worked successfully with CompAir on otherprojects, including the renowned English Channel Tunnel and anumber of other drilling applications across the world, where thecompressors had proved their reliability in a harsh environment.Various quotes were received from all the major compressormanufacturers, but it was our excellent track record in an identicalapplication, coupled with our local service capability that won theday.”

In order for the project to be completed on time and on budget,drilling must continue 24 hours a day, seven days a week,meaning that the L160 compressors have to performcontinuously. CompAir Canada was also the only compressormanufacturer that could offer its own, local service organization,helping Strabag to ensure that the compressors remain fullyoperational at all times. With its head office only 45 minutes fromthe site, CompAir provides a dedicated engineer, who hasundergone special health and safety training to allow him to workunderground, backed by a team of technical support staff.CompAir Canada also supplied an L37 rotary screw compressorcomplete with dryer, filters and additional ancillary equipment forStrabag’s maintenance cabin above ground.

Mono Rail Crane

Other simultaneous operations include a mono-rail crane systemattached to the tunnel crown that operates independently of theTBM and allows the rail to be moved forward as the TBMadvances. The rail, in 4.5m sections, is removed from behind thebored section of tunnel and transported over the back-up to a newsection, leaving behind a smooth tunnel floor. 'The simultaneousoperations result in less rolling stock and materials that must bemaintained. The rail does not have to be removed as a separatestep after the tunnel bore is complete,' says Mike Burngasser,Robbins Field Service Manager.

Control Room & Guidance System



Big Becky is controlled from a small room deep inside themachine. An operator uses computer screens and digital readoutsto monitor the equipment and the machine’s alignment. Thealignment measurements are accurate down to a scale of acouple of millimetres. Lasers are used to keep Big Becky on theright path, and although the route involves changes in grades, twovertical curves and three horizontal curves, Gschnitzer said there’svirtually no chance Big Becky could pop out in the wrong locationat the end of its journey. “That’s the least of my concerns,” he saidwith a chuckle.

Invert Structure

As part of the logistics process, Strabag will pour the final invertsection underneath a bridge system designed and supplied byBMTI (Austria), a sister company owned by Strabag. Once theTBM has advanced approximately 2.5 km (1.6 miles), the balanceof the final concrete section will be installed on a secondaryworking bridge, also supplied by BMTI. This system allows thefinal lining to be installed independent of the TBM boringoperation.

Time will be saved on the overall project schedule in other waysas well. The 12.5m finished diameter tunnel will require 50cmthick concrete lining with a waterproof membrane to prevent waterfrom leaking out of the tunnel. As the TBM bores, the tunnel will beconcurrently lined with in-situ concrete and PVC waterproofingmembrane.

The invert structure will be cast and set approximately 500mbehind the TBM boring operations, while the arch structure will beseparately cast approximately 1500m behind the machine. An87m long bridge will allow rubber-tired supply vehicles to travelover the invert concrete installation area. While the arch is cast,



the ventilation duct, continuous conveyor, supply pipes and powerlines will need to be temporarily removed from the bored tunnelwalls and diverted through the concrete formwork until they can bereattached to the completed tunnel walls further down.

The concurrent lining works will be started once the TBM hasbored ahead 1km.

The installation of the in-situ concrete liner continuous while boringis a first in North America and was initiated by Strabag in order toreduce the construction schedule and reduce the cost of thetunnel as compared to pre-cast segments, ' says Doug Harding,Vice President of The Robbins Company of Solon, Ohio.

The tunnel is being constructed in two passes with rock dowels,steel ribs, mesh and shotcrete, followed by a polyolefinmembrane and unreinforced 600-mm thick cast-in-place concretelining. The lining will be prestressed to resist internal waterpressure using a high-pressure 'interface' grout applied betweenthe shotcrete and the final lining. The combination of themembrane and prestressed lining system will prevent water fromentering the rock and resultant swelling. Two layers of membraneare being applied to the shotcreted rock enabling the spacebetween the membranes to be vacuum tested after installation inorder to ensure membrane integrity. The membrane will alsoprotect the concrete lining from the aggressive groundwaterconditions found in the Queenston Formation.

THE INVERT BRIDGE TRAIN

The Invert Bridge train is pouring finish concrete to the bottom 112° of thetunnel. The train is approximately 244 meters in length and contains twoform works consisting of 12.5 meter long bays. Each bay requires 120m3of concrete. With a crew of 20-21 workers working two shifts, the invertwill pour two bays daily. Typically it takes about 7 hours to pour one 12.5meter long bay. The drying time before the form is moved is 6-7 hours. Adouble layer of polyolefin (3 millimeters thick) waterproof membrane isbeing applied to the tunnel invert in advance of the final concrete pouring.



Arch Forms

THE ARCH FORMS

A double layer of polyolefin (3 millimeters thick) waterproof membrane isbeing applied to the tunnel wall in advance of the final concrete pouring.The membrane is attached to the Shotcrete coated wall by use of Velcro.The first arch form is always 2 bay lengths (one already poured and oneready for pouring) ahead of the second arch form. The front arch formpours every other bay, the rear arch form fills the gaps.

The Arch Forms being prepared

The Arch Forms are pouring the finish concrete to upper 248° of thetunnel lining. At the current time one shift is operating daily pouringconcrete into a 12.5 meter long bay. The concrete is poured continuouslyuntil the bay is filled. The concrete is poured on both sides of the form onan equal basis to ensure the form remains centered. During the pour,selected sections of the arch form vibrates by use of pneumatics. Thisvibration helps the concrete to settle and compress properly. Moisture isdrawn to the form and aids in forming a smooth surface skin. Accessportals on the arch form allow workers to aid the distribution and settlingof the concrete using handheld vibration tools. Typically it takes about 7hours to pour one 12.5 meter long bay of the arch form utilizingapproximately 240 m3 of concrete. Concrete is pumped through concreteports built into the arch form. After the concrete is poured the forms of thearch remain in place for 10 hours to allow the concrete to dry. Twenty-twomen are employed on the arch form. Currently, concrete is supplied to theforms from the surface via pipeline. This will continue for the initial 500meters. A support bridge is being prepared to attach to the arch form thatwill allow concrete to be delivered by vehicles as it progresses further into



the tunnel.

There are two Arch Forms in the tunnel. In the near future, both forms willbe utilized at the same time resulting in the pouring of a daily maximumlimit of 25 meters. The two forms work in tandem following behind amembrane liner. The Arch Form train is 368 meters in length.

The arch forms will pour 3-4 bays per week.

Grouting

GROUTING

There will be two different types of grouting:

1. the contact grouting to make sure that the inner lining concrete isproperly bedded, and 2. the pre-stress grouting to compensate for shrinkage and creeping ofthe inner lining concrete. Basically this is an substitute for reinforcement.

Restoration

The Restoration is taking place at two locations within the tunnel at the"Fall of Ground" and "St. David's Cathedral". It is a two stage restorationprocess to re-shape the tunnel. The first stage are abutments consistingof rockbolts, steel channels and reinforced shotcrete. The second stageconsists of steel panels that are suspended from the arch and are actingas a lost formwork for the shotcrete/concrete infill.



Intake Grout Tunnel

by Bermingham Foundation Solutions

Working in the water adds many challenges, including keepingtrack of extra safety measures. Workers were required to wearlifejackets and lifelines at all times.

A gigantic steel sheet cofferdam made up of seven interlockingislands constructed on the Niagara River half a kilometre aboveNiagara Falls is raising eyebrows in the engineering community.

At 200 by 450 feet, it is one of the largest cofferdams in theworld. It was built as the egress point for a huge tunnel boringmachine (TBM) building the 10.4-kilometre Niagara Tunnelproject. The TBM has a diameter of 47 feet – about 2.5 times thesize of the TBM used in the construction of the Toronto subwaytunnel and 1.5 times the size of the ones at the English Channeltunnels.

The steel sheets of the cofferdam are either 25 feet or 40 feet talland 5/8-inch thick. The template created a frame for theseinterlocking steel sheets. The distance and orientation betweencells had to be controlled so as not to lose the rhythm of thedesign. A bridge was built from shore to the first cell and the lastcell was rectangular and keyed into a slot in the pier. “Weencountered an unknown challenge, which was that there was alayer of silt that had to be removed, which was unexpected,” saidBermingham. “The silt was between one and two metres deepand had to be clamed from the bottom of each cell as it couldhave caused leaks and settlement. We had to clean and scour thebottom and hang a filter cloth on the interior of each cell.” Theschedule was a challenge as it was accelerated, saidBermingham.

“We originally had a two year schedule and then they wanted itdone in the first year, and we started three or four months latebecause of the soft overburden,” he said, “but we met theaccelerated date.”



Bermingham Foundation Solutions was contracted to design andbuild the cofferdam. Doug Nemec, project manager of theHamilton-based contractor, says the cofferdam has been acomplicated and risky job.

“Designing and building a giant cofferdam for the largest rockTBM in the world and installing it in one of the most powerful riversin North America can be daunting.

“It was a tribute to the entire team, that a project of this complexityand size was completed in the short construction window that theNiagara River allows,” adds Nemec.

Peter Smith, vice-president of the Bermingham, says the mostimportant factor during construction was to anticipate what couldgo wrong and plan ahead for it. “If we made a serious mistake, werisked the cofferdam filling with water.”

In most cofferdam projects, steel sheets are driven deep into theriverbed where the soil acts as a seal, but because the Niagarariverbed above the diversion dam is bedrock, Bermingham had tocome up with a different solution. It designed a series of seven55-foot diameter enclosures made up of interlocking steel sheets(plates on watertight bases) formed around a template thatessentially looks like “a Ferris wheel laying on its side”.

Most of the steel sheets are 25 feet tall; some are 40 feet tall,used where a slot was cut into bedrock for a new wateracceleration wall to ensure enough water entered the tunnel atforce to run the generators at Sir Adam Beck. The steel plates are5/8-inches thick.

Giant templates, which follow the riverbed’s contours, were madeto build a steel frame to hold the interlocking steel sheets tightly inplace.

To keep water out, divers installed sand bags at the inside baseof the structures and a 400-millimetre concrete layer was pumpedthrough a tremie pipe around the outside base and held down by15 feet of gravel, says Smith.

Once the massive cofferdams were constructed, the tunnel boring



machine had a clear pathway to bore through the Niagara Riverbed.

The final watertight measure taken was to drill 200-foot deepholes at the riverbed around the inside of the enclosures and“pressure inject” them with grout, says Smith. “Basically, theycreated a curtain of grout underneath the cofferdam so the watercan’t get in.” Geo-Foundations was the subcontractor retained forthe grout work.

They then filled each of the seven enclosures with gravel andremoved the templates. The enclosures were filled with graveland compacted to form islands for workers and equipment,including a 250-tonne mobile crane.

A bridge was constructed of rock rubble from shore to the firstenclosure. An interlocking concrete caisson wall, typical of shoringdone for highrises on downtown Toronto’s waterfront, built on theland side of the cofferdam ensures watertightness.

The last enclosure, unlike its circular neighbours, was rectangularand made to the width of the bridge piers. The enclosure waskeyed into the slot in the pier normally used for stop logs, Smithexplains.

To help divert more water from the tunnel, a precast concreteacceleration wall was built from a barge by McNally ConstructionInc. The contractor also blasted the slot in the riverbed about 70feet wide by 20 feet deep.

“We had to come up with a way of engineering the cofferdamthrough this area so it would be watertight.”

To accomplish that, 40-foot-long steel sheets were dropped tothe base of the cut-away slot and a diver marked the shape of thebottom on the sheets so they could be brought to the surface, cutwith torches and then re-installed.

Bermingham superintendent Brent Porteous says McNally workedclosely with Bermingham to schedule work so both contractorscould work in the water together.



Another challenge which added to the potential danger of the workwas the river’s fast-moving current, up to 20 knots – 25 miles perhour – in some places. Builders chose to work just upstream of adiversion dam to an old power station where the pace of thecurrent could be controlled, says Smith.

While the water above the diversion dam was calm, the operationwas still risky for workers, who were required to wear lifelines andlifejackets at all times.

“If you were to throw a stick into the water at the dam, four minuteslater it would be at the bottom of the falls,” Smith says.

Originally, Bermingham was given two years to plan and detail theproject, but because Strabag AG Inc. faced a late penalty clauseof $250,000 a day, it tightened the schedule, allowingBermingham only 14 months for the work.

Smith says the cofferdam is probably the largest built in Canadasince the St. Lawrence Seaway locks were constructed in the1950s.

When the tunnel bore breaks through to the tunnel’s 45-metredeep intake shaft in the middle of the river just upstream fromNiagara Falls, Big Becky will be disassembled and extractedpiece by piece via the shaft, which has been sealed against wateringress from the river above by a grout curtain designed andconstructed in 2007 by Geo-Foundations.

The intake shaft excavation will be 16 metres x 26 metres in plan x45 metres deep. Above the bedrock river bottom, the river is heldback from occupying the shaft excavation by a multiple-cellcofferdam built of sheet piling and rock fill. Below the cofferdam,in the bedrock itself, the grout curtain constructed by Geo-Foundations works to seal the rock fissures – formed by cracks,open horizontal bedding planes and plunging joint networks – thatwould certainly, without treatment by grouting, let enough waterpass into the shaft excavation to cause flooding detrimentalenough to halt all further shaft construction. The grout curtain willsee its sternest test in the interim between completion of the shaftexcavation and the tunnel boring’s eventual breakthrough – the



grout curtain will have to resist 45 metres of hydrostatic headacross its relatively thin width. Grouting of the fissured bedrockincluded full depth, fourth-order split spaced holes and employedsimultaneous grout injection at multiple holes. A sophisticatedsuite of drilling and grouting equipment was used, including water-hammer drilling, real-time, response driven additive dosing tomodify grout formulations during grout injection and an automatedbulk grout batching plant capable of delivering more than 20 cubicmetres of cement grout per hour. Grout curtain constructionrequired more than 13,000 lineal metres of drilling and consumedmore than 541,000 kg (dry weight) of cement. Several verificationholes were drilled and two holes were core sampled and testedfor residual hydraulic conductivity as part of grout curtain qualityassurance.

The objective of the cofferdam project was to create a safe placefor Becky to exit from her 11.5 kilometre journey.

It was a cellular, gravity type cofferdam to be constructed on barerock, which is not common, that needed to be able to withstandwater and ice pressure for years. The biggest challenge was theabsence of any soil that could be used as support. Safety was ourfirst and last job each day and workers were required to wearlifelines and lifejackets.” The project presented many challengesincluding design build, insurance, schedule and manpower as wellas seating the cofferdam on the river bottom. The company made3D models in-house and used a template, which had to be leveledso each cell would carry an even load. Divers installed sand bagsat the inside base of the cells and a concrete layer was pumpedaround the outside base and held down by 15 feet of gravel. Twohundred-foot deep holes were drilled into the riverbed around theinside of the cells. The holes were then pressure injected withgrout.

The Niagara River Cofferdam, at 200 by 450 feet, is one of thelargest cofferdams in the world said Patrick Bermingham ofBermingham Construction at the 80th Annual ORBA Convention inToronto. The steel sheet cofferdam, located at the Canadian sideof Niagara Falls, was constructed for use with the Niagara Tunnelproject and consists of seven interlocking cells. known as the



world’s largest diameter tunnel carry water from the river to the SirAdam Beck Power Station to generate hydroelectricity.

Stop-Log Gates

The intake gate is comprised of 10 steel stop logs. Each is 13.5meters wide for a total height of 14.8 meters. The combinedweight of all 10 sections are approximately 215 tonnes (enoughsteel to make 260 average cars) . The lowest gate holds back awater depth of 38.6 meters, which results in a water pressure ofalmost 4 Bar (60 psi).

Geology

The geology is varied, consisting of limestone, dolostone,sandstone, shale and mudstone. The rock strength ranges from15 to 180 MPa (2,100 to 26,000 psi), with most of the rock in the40 to 100 MPa (5,800 to 15,000 psi) range. With the exception ofsandstone, the geology is basically nonabrasive. Most of thedebris (approximately 30 percent) removed from the tunnel willconsist of Queenston shale.

During the first 200 m (656 ft), problems were encounteredincluding higher than expected water inflows and handling of thewater due to the 7.82-percent decline. The water removal systemhas been modified and the progress has increased to theexpected advance rates. After 850 m (2,780 ft) of excavation, theTBM entered the Queenston shale formations. Horizontal banked



layers, which were not able to arch until rock support was placed,led to huge over-break and caving up to 3 m (10 ft) above the roofshield in the L1 area. Strabag designed a special ground supportmethod with grouted umbrella spiles to mine through this geology.

As part of the logistics process, Strabag will pour the final invertsection underneath a bridge system designed and supplied byBMTI (Austria), a sister company owned by Strabag. Once theTBM has advanced approximately 2.5 km (1.6 miles), the balanceof the final concrete section will be installed on a secondaryworking bridge, also supplied by BMTI. This system allows thefinal lining to be installed independent of the TBM boringoperation.

The tunnel is located predominantly in Queenston shale withsome limestone, dolostone, sandstone and mudstone up to 200MPa (29 ksi) UCS.

The rock along the tunnel bore path is known to have high in-situstress and there is potential for squeezing ground. An initial rocksupport lining of wire mesh, steel ribs, rock bolts, and shotcretewill be installed as the TBM advances.

After tunnel excavation is completed, an in-situ placed concretelining will be installed, and the final lining will include awaterproofing membrane system to ensure that water does notseep from the tunnel into the rock and cause swelling.

Rock swelling in the Queenston Formation is caused by acombination of reduced in-situ stresses in the rock surroundingthe tunnel and availability of a source of fresh water from within thetunnel. The pore-water of the Queenston Formation is highlysaline and, through a process of pore-water dilution and iondiffusion, the clay minerals in the rock expand and absorb waterresulting in swelling of the rock. This process would impart largepressures on the tunnel linings if these conditions are allowed tooccur.

Extensive modeling of the swelling process and its effects on theload build-up on tunnel linings were studied throughout the 1990s.Modeling included development of a 'swelling law' to characterize



the relationship between swelling and in-situ stresses. In thismaterial, swelling decreases in proportion to in-situ stresses andceases altogether at a confining stress between 4 and 5 MPa.The entire process was modeled using specially developed 'Fish'routines for the 2D FLAC geotechnical analysis program. Variousoptions for dealing with the stress build-up were consideredincluding very high-strength liners and compressible grouts.

The tunnel has various technical challenges, not the least of whichis that it is situated in a geologic phenomenon known as theQueenston Formation, a mudstone that swells when exposed tofresh water. The potential for swelling has been a major challengethroughout development of this project.

Hatch Energy’s involvement with this project dates back to 1989with Phase 1 definition studies of the Niagara River HydroelectricDevelopment (NRHD) for development of additional hydroelectricfacilities at the Sir Adam Beck (SAB) Generating Complex. In theearly 1990’s, Hatch Energy (then Acres) participated in Phase 2definition studies including construction of an underground testexcavation to determine the constructability of undergroundexcavations in the Queenston rock formation.

The NRHD project consisted of twin 10.4-km diversion tunnels, anunderground powerhouse, and intake/outlet structures near theexisting Sir Adam Beck 1 and 2 powerhouses. Detailedgeotechnical investigations were performed as well as anextensive testing program to determine swelling and othercharacteristics of the Queenston Formation. Hatch Energy alsoparticipated in preparation of the Environmental Assessment thatwas approved by Ontario’s Ministry of Environment in October1998. The approved project included construction of twoadditional diversion tunnels and an underground generating stationnorth of the existing SAB generating stations.



Tunnel Crews

The tunneling crew operates the TBM and equipment 24 hours aday, seven days a week. About 30 crew members are onsite in agiven shift, with one maintenance shift each morning in order tomonitor and test the equipment. The crew has endured winterconditions reaching below -20°C at the jobsite, which caused theconveyor systems to freeze over with ice. Antifreeze was sprayedon the affected conveyors and the ice was chipped off in order tokeep them running. Big Becky is now operating on a 24-hour-a-day, seven-day-a week basis. The typical day is divided into twoproduction shifts and a maintenance shift. About 30 people areneeded to crew Big Becky during each shift.

An onsite geologist monitors progress, watching for any dangersigns.

As the machine moves forward workers erect steel ribs in a fullcircle around the tunnel every few feet to reinforce the rock. Therock surfaces are then covered with a heavy wire mesh and alayer of concrete is blown on top to form a temporary shell.

Eventually, the entire tunnel will be lined with concrete slabs abouttwo-feet thick and a waterproof liner will be installed. The designwill give the tunnel a minimum 90-year life span.

An overhead conveyor belt is used to transport the chewed uprock from the cutting head to the surface. Dump trucks haul thematerial, which will later be used to make bricks, to a nearbylocation that was cleared as a temporary storage site.

The underground operations are supported by staff working onthe surface. To supply concrete to the tunnel, a concrete plantwas built on the surface just above the tunnel’s entrance. There’salso a small water treatment plant that’s used to clean waterpumped out of the tunnel before it’s dumped into the nearbyhydroelectric canal.

Inside the tunnel away from the tunnel entrance, the air



temperature is roughly 10 C. Gschnitzer said the rock itselfregulates the temperature, which increases another 10 C whenBig Becky is running.

The mechanical energy exerted by the machine is enough towarm the tunnel. “It heats itself,” Gschnitzer said.

The average pay for each worker is $150,000 - $200,000 per

annum.

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