design and construction of foundations for the saint lawrence river bridge, autoroute 30 montréal...

7/22/2019 Design and Construction of Foundations for the Saint Lawrence River Bridge, Autoroute 30 Montral Quebec

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Design and Construction of Foundations for theSaint Lawrence River Bridge, A30 Montral

Andrew Cushing, Robert Talby, Ivan Hee, and Andy DoddsArup Canada,Inc. Toronto, Ontario, CanadaDavid Garcia CuetoNouvelle Autoroute 30 CJV, Montral, Qubec, Canada

ABSTRACTThe final portion of the Autoroute 30 to the south and west of Montral opened to the public in December 2012. A majorcomponent of this landmark project included the construction of a 1.8km long bridge over the Saint Lawrence Riverbetween Les Cdres and St. Timothe. This paper provides a summary of key aspects of the bridges foundation designand construction. These include the geological investigations prior to and during construction, addressing lateral seismicand ice impact loading in the foundation design, temporary works construction (including temporary access bunds andfoundation cofferdams), overburden soil and rock excavation, rock surface inspection in the wet and dry, micropileinstallation and testing, and concreting in cold-weather.

RSUMLe dernier tronon de l'autoroute 30 au sud et l'ouest de Montral a t ouvert au public en Dcembre 2012. Unecomposante importante de ce projet capital comprenait la construction d'un pont dune longueur de 1,8 km sur le fleuveSaint-Laurent entre Les Cdres et Saint-Timothe. Ce document prsente un rsum des principaux aspects de laconception et de la construction des fondations du pont. Une attention particulire est accorde aux tudes gologiquesavant et pendant la construction, les effets des charges dimpact, sismiques et en provenant de la glace sur laconception des fondations, la construction temporaire des travaux (y compris les jets de roc d'accs temporaires et lesbatardeaux), le mort-terrain et l'excavation du roc, l'inspection de surface de la roche, l'installation, en conditionssubmerges et sches, des micropieux et d'essais, et les dtails de btonnage par temps froid.

1 INTRODUCTION

The Nouvelle Autoroute 30 (A30) Public PrivatePartnership (PPP) construction project is located southand west of the island of Montral, between Vaudreuil-Dorion and Chteauguay in Qubec, Canada. The designand construction was carried out over a four year period

on a design-build basis by the Nouvelle Autoroute 30Construction Joint Venture (NA30 CJV), comprised ofDragados Canada, Acciona Infrastructures Canada,

Aecon, and Verrault. Lead design services were providedby Arup.

This paper is focused on the design and constructionof the foundations for the A30 bridge over the SaintLawrence River between the townships of Les Cdresand St. Timothe, as shown in Figure 1.

2 BRIDGE CONFIGURATION

The bridge has a total length of 1.8 km and includes twoseparated decks, each supporting a two lane highway asshown in Figure 2. Each deck is supported by 2

abutments and 41 piers with a typical span length of 45m,which includes a single abutment on each bank of theriver, resulting in a total of 82 individual foundation units.The decks are supported on single columns which are inturn supported by isolated pad footings bearing directlyonto rock. Each footing is anchored to the rock withdrilled and grouted micropiles (between 8 and 28micropiles at each footing, depending upon water depthand column height) to resist sliding and overturning due toice loading and in the event of an earthquake.

3 GEOTECHNICAL SITE INVESTIGATION ANDTESTING

At the start of the tender design (mid-2007), only sixhistorical borings were available at the Saint LawrenceRiver Bridge site. These borings were used to develop a

tender design submitted in March 2008. Shortly after thepreferred bidder was announced in June 2008, NA30 CJVimplemented a project-wide site investigation for detaileddesign starting in August 2008 which ran through to theend of the year. During this 2008 site investigation(performed by InspecSol of Montral), a total of 42boreholes were advanced at the Saint Lawrence RiverBridge site, with a minimum of one boring for each pair offoundation units. The location of each borehole wascentered at the eastern and western piers in analternating fashion. Disturbed split spoon sampling wasobtained in the overburden soils, while NQ-caliber doublecore barrel drilling was used to obtain rock core samples.Rock testing included unconfined compression (UCS) withstrain measurements and Brazilian tension (splitting)

testing.A series of additional boreholes were advanced in the

summer of 2009 to investigate a zone of disturbed rockcentered near Piers 15 and 16 (closer to the northernshoreline) that was identified in the 2008 investigation.

Once construction started at the bridge site in the fallof 2009, destructive holes were advanced at locationswith no available corehole to investigate the potentialpresence of vertical joints below rock formation level.

Another series of coreholes were advanced at footing unitlocations not yet excavated which were not cored in 2008.


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Figure 1. Autoroute 30 PPP Route Alignment With Location of the Saint Lawrence River Bridge

Figure 2. Saint Lawrence River Bridge Superstructure and Substructure Configuration


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4 GEOLOGIC AND SUBSURFACE CONDITIONS

4.1 Typical Conditions

The bedrock at the Saint Lawrence River bridge site istypically characterized as strong to very strong light grey

quartzitic sandstone with beds of medium to dark greyslightly dolomitic sandstone. The bedrock geology at thenorthern portion of the bridge is typical of the CambrianPostdam Group (Cairnside Formation), while at thesouthern portion it is typical of the Lower OrdovicianBeekmantown Group (Theresa Formation).

The quartzitic sandstone rock is typically fresh or onlyslightly weathered with moderately close to widely spaceddiscontinuities. The dolomitic sandstone is typicallyslightly weathered with moderately close to closediscontinuities, and the presence of small vugs werenoted in some cases. The rock is horizontally bedded,and thin black shale beds were encountered between 3mand 6m below the rock line in selected borings.

A summary of the stratigraphy encountered at the

Saint Lawrence River Bridge site is provided in Table 1. Ageneralized cross-section of the bridge is provided inFigure 3, showing the position of the deck, the piers andabutments, depth to rock, overburden thickness, andminimum / maximum water levels.

4.2 Localized Disturbed Zone

A number of boreholes confirmed the existence of a zoneof disturbed rock around Piers 15 and 16 (closer to thenorthern shoreline), with an estimated width ofapproximately 60m. Two types of disturbance weredescribed within the rock core: (i) contemporaneous'slumping', indicating fault movement soon afterdeposition, and (ii) a later, more brittle fracturing and

faulting. Much of the brecciated texture appeared to becontemporaneous slump breccia. The total core recovery(TCR) and rock quality designation (RQD) were affectedby the later brittle faulting rather than the presence of the'slump breccia'.

The disturbed zone was interpreted as an ancient faultzone at the interface of the older Cambrian PotsdamGroup (Cairnside Formation) with the younger OrdovcianBeckmantown Group (Theresa Formation). The faultcorresponds with a N120 fault identified on the TectonicMap of Canada (1969), and is believed to have developedin the Proterozoic (greater than 570 million years ago).The last major movement of similarly oriented faults isinferred to be in the Cretaceous period, approximately 125million years ago (Rocher, et al., 2003). The identifiedfault is therefore not considered to be active, and risk offault rupture is considered to be very low.

4.3 Rock Quality Designation (RQD)

The RQD of the bedrock cores varied between 0 and100%, with approximately 80% of the recorded RQDvalues in excess of 70%. All but four of the zero RQDvalues were recorded within the upper 1m of rock, which

is typically slightly more weathered. Relatively lower RQDvalues are apparent in the disturbed zone.

4.4 Intact Rock Strength (UCS)

Unconfined compressive strength (UCS) testing wasperformed on 51 samples of intact bedrock obtained

during the historical and 2008 ground investigations. Asummary of this data is provided in Table 2. Analysis ofUCS data obtained in the disturbed rock zone aroundPiers 15 and 16 is also shown in Table 2 in recognition ofrelatively lower intact strength results. An intact UCSdesign value of 150MPa was considered appropriate forthe Cambrian and Ordovician Groups outside of thedisturbed zone. In the disturbed zone, an intact UCSdesign value of 82MPa was adopted.

4.5 Hoek-Brown Mohr-Coulomb Strength Parameters

An effective cohesion intercept (c) of 10MPa and effectiveinternal friction angle () of 41 was assessed for thebedrock based on Hoek-Brown and Mohr-Coulomb

strength relations (Wyllie and Mah, 2004). Reducedstrength parameters corresponding to a c value of 5MPaand value of 36 were assessed for the rock in thedisturbed zone.

4.6 Intact Rock and Rock Mass Stiffness

Intact rock stiffness was measured with strain gaugesduring UCS testing. Little difference was apparentbetween the Cambrian and Ordovician Groups, withaverage modulus-to-strength ratio values of 284 and 306,respectively.

Rock mass stiffness is somewhat less than that ofintact rock due to the presence of discontinuities. Rockmass stiffness is difficult to measure without large-scale

in-situ tests. However, rock mass stiffness may beestimated in several ways, for example:

Emass = (2 RMR) 100 (GPa) [1]

where RMR is the Rock Mass Rating after Bieniawski(1974). RMR is calculated on the basis of the massproperties of the rock, such as joint spacing andgroundwater conditions. A typical RMR of 75 wasestimated for the rock mass at this site, giving Emass =50GPa. In the upper 1m or so, where rock is moreweathered and fractured, an RMR of 60 was deemedmore appropriate, giving Emass = 20GPa.

Another empirical relationship has been proposed by

Hoek and Brown (Wyllie and Mah, 2004) based on asystem similar to Bieniawski. This indicates an Emass of35GPa would be appropriate for typical rock massconditions based on an unconfined compressive strengthof 150MPa for intact rock. An Emass of between 20GPaand 50GPa was therefore considered appropriate fordesign. A reduced Emass of approximately 7GPa for rockwithin the disturbed zone was assessed based on theestimated Hoek-Brown parameters.


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Table 1. Summary of Stratigraphy at Saint Lawrence River Bridge, Autoroute 30

Stratum (Locations)Highest Top

El. (m)Lowest Base

El. (m)Maximum

Thickness (m)Fill (Abutments and Land Piers) 29.5 28.6 0.8

Champlain Deposits (Abutments and Land Piers) 34.1 30.6 2.2Alluvial Deposits Clay (Water Piers) 30.0 24.3 2.1Alluvial Deposits Sand and Gravel (Water Piers) 27.3 22.0 2.4Glacial Till Deposits (Abutments and Land Piers) 32.8 19.2 4.6Cambrian and Ordovican Sandstone Bedrock (All Locations) 29.8 19.2 -

(1) Base not proven. Highest top and lowest base refers to maximum and minimum top of rock elevations.

Figure 3. Saint Lawrence River Bridge Generalized Structure and Geologic Cross Section

Table 2. Summary of UCS Data for Bedrock Geology

Cambrian OrdovicianDisturbed

ZoneUCS (MPa)

Minimum 142 64 64Maximum 265 300 96Mean 196 184 82(No. of Tests) (14) (37) (4)

5 FOUNDATION DESIGN

5.1 Basis of Design

Design of the Saint Lawrence River Bridge foundationswas undertaken in accordance with the Canadian

Highway Bridge Design Code (CSA, 2006). This codeadopts a limit state design approach in which thefactored resistance (either structural or geotechnical) mustequal or exceed each and every factored loadcombination. At the ultimate limit state (ULS), thefactored geotechnical resistance is obtained by multiplyingthe ultimate geotechnical resistance, calculated usingunfactored rock parameters, by a resistance factor.

The resistance factors specified in the code which areapplicable to the Saint Lawrence River Bridge foundationdesign are presented in Table 3. They are a function of

foundation type, loading mode (compression or tension),and how the ultimate geotechnical resistance isdetermined (i.e., from a static analysis estimate ormeasured directly by a static load test).

As both pre-production and production load testing ofmicropiles was performed on site, a resistance factor of0.6 was used to evaluate the factored ULS tensileresistance of these foundation elements.

Table 3. Resistance Factors for Foundations (CSA, 2006)Resistance Factor

Static AnalysisEstimate

Static LoadTest

Deep Foundations(Tension)

0.3 0.4

Shallow Footings

(Sliding)0.8

Shallow Footings(Bearing)

0.5

5.2 Design Parameters

Bearing Capacity

Based on the typical rock core descriptors assessed fordesign, a factored geotechnical resistance at the ultimate


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limit state (ULS) for bearing resistance equal to 12.5 MPawas recommended for the undisturbed rock designcategory. A factored geotechnical resistance at ULS forbearing resistance equal to 6.5MPa was recommendedfor the disturbed rock design category. The lower designvalue for the disturbed rock design category addressedthe potential for greater settlement under serviceability

limit state (SLS) loading conditions and reducedresistance to shear leading to possible bearing relatedfailure under ULS loading conditions. Footingperformance for the SLS was considered to be moresignificant for both design categories.

Base Shear Resistance

An interface friction between the footing and bedrock basewas used to define base shear resistance, where the baseshear resistance is equal to the normal force acting on thebase multiplied by the interface friction coefficient. Thefollowing factored ULS interface friction coefficients wererecommended for design: 0.4 for footings constructed underwater (ultimate

interface coefficient = 0.5); 0.6 for footings constructed in the dry (ultimate interfacecoefficient = 0.75).

The possibility of some soil and/or sediment remainingon bearing surfaces constructed underwater wasaccounted for by adopting ultimate interface friction valueappropriate to a clayey-gravel base material.

Micropile Tension Resistance

The design geotechnical capacity of each micropilecorresponded to a maximum factored tension load of1.8MN. Hence, the factored geotechnical resistance mustequal or exceed this value.

Pre-production load testing results proved an ultimate

grout-to-rock shear stress of 1662kPa, with a factoredbond stress of approximately 665kPa. The typicalmicropile bond length of 6m provided a factoredgeotechnical tensile resistance of 1.9MN.

6 FOUNDATION COMPONENTS

6.1 Blinding Layer

An unreinforced layer of concrete (or blinding layer) wascast against cleaned and competent bedrock toaccommodate variations in rock elevation and to provide alevel surface at a defined elevation so that the subsequenttremie plug reinforcement could be placed accurately.The minimum specified thickness was 150mm, while themaximum permissible all-around unconfined thicknesswas limited to 850mm at the center of the footing.Localized unconfined thicknesses of up to 1150mm werepermitted, provided that this higher value covered nomore than one-third of the overall pier footing bearingarea. Any depth of blinding concrete which was confinedlaterally by competent bedrock was not included in thecomputation of its overall thickness, as such concretesimply replaced over-excavated rock.

While initially envisioned to be placed exclusively asan independent underwater (tremie) pour, the blindinglayer was placed on site (as an independent pour)exclusively in the dry. In instances where the reinforcedconcrete plug was placed underwater using tremiemethods, the plug rebar cage was successfullysuspended from the top of the cofferdam, with the plug

and blinding layer concrete being placed in a singleintegral pour, effectively increasing the concrete cover onthe bottom of the plug.

6.2 Reinforced Concrete Plug

For the piers located in deeper water, a 6m squarereinforced concrete plug was installed directly above theunderlying rock (or blinding layer). Its main purpose wasto serve as a pedestal to transfer loading from the 4.5msquare pier footing above to the underlying competentbedrock below. The decision to incorporate a concreteplug in the foundation design was driven by limitations onthe pier column height for a given column diameter, aswell as the need to provide hydraulic cut-off and partial

counterweight to resist buoyancy to permit cofferdamdewatering for subsequent pier footing construction in thedry. The plug rebar cages were fabricated with somedegree of flexibility so the plug height could be adjusted toaccommodate fluctuations in the encountered rock levelrelative to the anticipated level. In instances where lowerthan anticipated rock levels were encountered, all effortswere made to first lengthen the column as much aspossible and then thicken the plug if required, as thisapproach minimized the resulting volume of additionalconcrete.

6.3 Reinforced Concrete Pier Footing

Reinforced concrete pier footings, with a 4.5m square

footprint, were constructed to transfer the load from thesingle supporting column above through the plug below tothe lower rock. The micropiles extended through the plugand into the pier footing, with the tension of the micropilesbeing transferred to the concrete in compression andshear with the use of galvanized steel plates, as shown inFigure 6.

6.4 Micropiles

More than 1400 micropiles were installed, eachcomprising of a 65mm diameter (Grade 1035MPa)threaded and galvanized steel bar with double corrosionprotection (i.e. minimum 5mm grout encapsulation withina corrugated HDPE sheath) inserted into a 150mmdiameter hole. A grout tube was installed full-length alongthe encapsulated rebar to ensure full grout contact alongthe entire bond length in the underlying rock, which wastypically 6m, but increased locally to either 7m or 9.5m ata total of 8 footing units (4 piers) as a consequence of azone of disturbed rock at these locations.

The micropiles extend through the lower plug and intothe concrete pier footing above. Micropiles situated in thecorners had reaction plates embedded within both theplug and the footing (Figure 6) to provide hydraulic uplift


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resistance to the plug in the temporary constructioncondition. The micropiles act as passive tensionelements.

Pre-production uplift testing was performed onsacrificial micropiles to validate the values of unit sideresistance for the micropile design. In addition, twomicropiles at each footing were randomly selected for

proof testing during production installation.7 TEMPORARY WORKS FOR FOUNDATION

CONSTRUCTION

7.1 Temporary access bunds

Temporary works for the A30 Saint Lawrence RiverBridge started in the fall of 2009 when access bundscomprised of crushed rock and gravel were installed fromthe northern and southern banks of the river. With theexception of nine bridge piers situated within the deepestwater, access to all other piers over shallower water wasprovided by these bunds.

As the river level was controlled by hydroelectric dams

both upstream and downstream of the A30 alignment, themaximum anticipated water level was known with morecertainty. The draft of the bunds and all temporarycofferdams was designed accordingly.

7.2 Temporary cofferdams

The construction of all underwater bridge pier foundationsrequired a temporary cofferdam of some type.Construction of the bridge pier foundations directlyaccessible from the temporary access bunds in shallowerwater closer to the shorelines started with excavation ofriverbed sediments (including boulders and cobbles) andfractured and weathered rock using a long-arm excavator.

A temporary cofferdam with an approximate square

footprint was then placed at each of the eastern andwestern foundation pad locations. These squarecofferdams were comprised either of driven sheet pilinginstalled around a steel template or pre-fabricated steelwalls with a tapered cutting shoe at the base (Figure 5).In each case, the positioning of the cofferdam was aidedby a driven steel spud in each of the four corners of thecofferdam. Grouting was sometimes used to seal theinterface between the bottom of the cofferdam andunderlying rock to control the water inflow rate duringdewatering. Additional riverbed debris and fractured rockwas then removed from the interior of the cofferdam.

For the nine piers not directly accessible from thebunds, cofferdams comprised of driven sheet piling wereinstalled using construction equipment on barges, witheach such cofferdam encompassing both the eastern andwestern foundation pads simultaneously within a largerrectangular footprint. To facilitate driving the sheet pilesthrough boulders and cobbles, a heavy chisel wasdropped through a steel pipe situated within the sheet pilerecess to break up such obstructions. For environmentalreasons, all excavation was performed exclusively fromwithin these nine cofferdams.

8 FOUNDATION CONSTRUCTION SEQUENCE

The construction sequence for the Saint Lawrence RiverBridge foundations where the plug rebar placement andconcreting was performed underwater is shownschematically in Figure 4. A step-by step narrative of theconstruction sequence is provided as follows:

(a) cofferdam installation, with toe of cofferdam at ornear the rock surface (excavation was typically performedprior to cofferdam placement, especially in shallowerwater); (b) excavation of soil and rock from within thecofferdam in deeper water, and installation of internalbracing; (c) placement of bottom plug rebar cage,micropile sleeves, and tremie concreting of the bottomplug; (d) cofferdam dewatering; (e) micropile drilling,placement and grouting from a working platform on top ofthe cofferdam, and footing construction (in the dry).

In instances where the plug rebar placement andconcreting were performed in the dry (i.e., for land piersand shallow water piers), all overburden excavation wasperformed prior to placement of the cofferdam. Thecofferdam was then dewatered during rock formation

inspection, followed by supplemental rock excavation (ifrequired), blinding concrete placement, plug rebarplacement and concreting, and micropile drilling andgrouting.

9 ROCK FOUNDATION INSPECTIONPROCEDURES AND REQUIREMENTS

A third party (InspecSol of Montral) was responsible forinspecting the condition and cleanliness of the exposedrock surface immediately prior to the placement of theplug rebar cage and concrete. Initially, these inspectionswere performed exclusively in the dry and were comprisedof visual inspection of the rock surface, evaluation of the

rock mass relative to photos and logs of the extractedrock core (where available), and intrusive probing of eithera pre-existing cored borehole or a destructive holeadvanced in the dry from the exposed rock surface. Theintrusive probing was intended to quantify the thickness,depth, and infill properties of perceived vertical jointslocated beneath the exposed rock surface. For footingsconstructed in deeper water, inspections were primarilyvisual, performed underwater with the aid of aprofessional diver via CCTV video connection. A coredborehole was available for comparison to the visualinspection at each such location.

The general requirements for the rock on which thefootings were to be founded included a minimum RQD of75%, a minimum TCR of 85%, and a maximum surfacesediment thickness of 5mm. Within the disturbed zone ofsedimentary breccia located at piers 15 and 16, theminimum values or RQD and TCR were locally reduced to50% and 75%, respectively. As values of RQD and TCRwere only available at 1.5m depth intervals along the rockcore, the evaluation criteria were supplemented by thefollowing limits on the cumulative permissible thickness ofinfilled vertical joints below proposed formation level: The top 500mm underlying the formation level must be

free of any weak layers (vertical joints);


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The total thickness of infilled joints must not exceed100mm between 500 and 1000mm depths;

The total thickness of infilled joints must not exceed200mm between 500 and 2000mm depths.

These limitations were based on the structural engineersrequirement to control vertical settlement of the far cornerof a pier foundation to less than 15mm (under a factored

ULS bearing pressure of approximately 12.5MPa basedon the most onerous eccentric loading condition). Whenthese specific requirements were not met in the field, thecondition was evaluated for settlement using footing-specific bearing pressures, assuming a 1-on-1 load shedthrough the rock layers, and a conservative estimate of

joint infill stiffness.

10 COLD WEATHER CONCRETING REQUIREMENTS

The construction of the foundations of the Saint LawrenceRiver Bridge was conducted year-round. Hence, specialmeasures were taken during the winter months in theconcreting of these substructures. Winter concretingrequirements for bridges in Quebec are set forth in the

CCDG (2009), as summarized below.

10.1 CCDG Concrete Temperature PlacementRestrictions

According to the CCDG, all concrete shall maintain aminimum temperature of 10C for a minimum period of 7consecutive days following concrete placement or until theconcrete has achieved a minimum of 70% of its required28-day compressive strength, whichever is longer. Afterthe protection period, the temperature of the concrete canbe lowered during the first 24 hours at a rate no fasterthan 10C/hour. The concrete shall not be put in contactwith the external air if the difference between the concretetemperature and air temperature is greater than 20C.

Underwater (tremie) concreting is prohibited at watertemperatures below 5C, and concreting in the open air isprohibited if the temperature of the external air is below0C. Type 1 protection must be provided if the externalair temperature drops below 5C within 48 hours followingconcrete placement.

10.2 CCDG Concrete Protection Types

The CCDG describes three types (levels) of concreteprotection during cold weather placement. During theconcreting of the St. Lawrence River Bridge foundations,two different types of protection were employed, asdescribed below:Type 1 protection: Completely covering all concretesurfaces with layers of impermeable insulating material

(sheets of foam with closed cells having an RSI thermalresistance of 0.40) with a minimum overlap of 75 mm.Type 2 protection: Construction of an impermeable andstrong enclosure around the concrete structure withheating appliances to generate and circulate a stream ofhot air inside the enclosure to maintain the concrete at therequired temperature.

11 SUMMARY AND CONCLUSION

This paper has presented key aspects of the design andconstruction of the foundations for the Autoroute 30 SaintLawrence River Bridge near Montral, Qubec. Thefoundations consist of 6m square pads bearing on strongto very strong light grey quartzitic sandstone. In an effort

to limit the plan area and weight of these foundations toresist sliding and overturning derived from ice impact andearthquake forces, over 1400 micropiles were installed toact as passive tension elements.

Extensive temporary works were required to constructthe bridge foundations, including temporary access bundsconstructed from the northern and southern riverbanksalong with temporary cofferdams. Bridge foundationswere constructed and inspected both in the dry andunderwater. Foundation inspections in the dry consistedof visual inspection supplemented by physical probing of acored or destructive hole to investigate the presence ofunderlying vertical joints, while underwater inspectionswere performed visually via CCTV with the aid of a diver.

As foundation construction was performed year-round,

winter concreting procedures were employed, whichconsisted either of providing insulation to contain the heatof hydration of the concrete, or construction of enclosureswith active heating.

REFERENCES

Bieniawski, Z.T. 1974. Geomechanics classification ofrock masses and its application in tunneling. Proc. 3rdInt. Cong. Rock Mechanics, Denver 2 (2), pp. 27-32.

Canadian Standards Association (CSA). 2006. CanadianHighway Bridge Design Code (andCommentary) CAN/CSA-S6-06.

Canadian Geological Survey. 1969. Tectonic Map ofCanada.

CCDG. 2009. Cahier des Charges et Devis Gnraux Infrastructures Routires Construction et Rparation,Ministre des Transports du Qubec.

Hoek, E. and Brown, E.T. 1997. Practical Estimates ofRock Mass Strength. International Journal of RockMechanics and Mining Science 34(8): pp. 1165-1186.

Rocher, M., Tremblay, A., Lavoies, D., AND Campeau, A.2003. Brittle fault evolution of the Montreal area (StLawrence Lowlands, Canada): rift-related structuralinheritance and tectonism approached by palaeostressanalysis. Geol. Mag. 140 (2), pp. 157172.

Wyllie, D.C. and Mah, C.W. 2004. Rock SlopeEngineering: Civil and Mining, Fourth Edition, SponPres, London and New York.


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(a) (b) (c)

(d) (e) (f)Figure 4. Underwater Foundation Construction Sequence: (a) cofferdam installation; (b) soil and rock excavation, internalcofferdam bracing; (c) placement of bottom plug rebar cage, micropile sleeves, and tremie concreting of bottom plug; (d)short-term (or longer-term) cofferdam dewatering; (e) micropile drilling, placement and grouting from a working platformon top of the cofferdam, either in the wet or dry; (f) footing construction (in the dry)

Figure 5. Temporary Cofferdam Assembly Figure 6. Footing and Column Reinforcement Placement

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