North American Tunneling 2006 – Ozdemir (ed.)© 2006 Taylor & Francis Group, London, ISBN 0 415 40128 3

Shotcrete constructed cut and cover tunnel portal

Leon JacobsFrontier Kemper Constructors, Inc.

Kurt ZeidlerGall Zeidler Consultants, LLC

Anthony MurthaNew Jersey Transit Corporation

ABSTRACT: The reconstruction of the Weehawken Tunnel for the New Jersey Transit Hudson-Bergen LightRail System is about to be completed. The more than $145M contract encompasses the enlargement of runningtunnels, the construction of an access shaft for the new underground station and new portals.A series of innovativeconstruction techniques have been applied to meet the challenging project requirements and aggressive schedule.The contract design called for a permanent portal structure with a trumpet-shaped roof geometry, while the side-walls funnel out towards the tunnel entrance. The structure started in the mined section and lead to the portal. Thecurved sidewalls for the portal structure were converted to vertical concrete walls complying with the contract’sgeometric requirements. For the roof portion, reinforced, high-quality shotcrete was used to form the complexcontour. The membrane tunnel waterproofing was extended to the portal face wall. Construction of the newportal was timely completed while meeting the quality requirements stipulated in the Contract Documents.

1 INTRODUCTION

A Value Engineering Change Proposal (VECP) wasdeveloped and accepted which proposed to substitutethe planned cast-in-place concrete lining at the eastportal mined section, transition section to the cut-and-cover section and the east portal cut-and-coverwith a shotcrete lining. The proposed shotcrete liningprovides an equal product to the contract’s cast-in-place concrete. While providing an equal product,the concrete spray-on process provides for greaterflexibility in its application mainly due to the geomet-rical configuration. In contrast to the contract design,the spray-on process allows for a ‘smooth’ geometricarrangement of the bifurcation between the tunnel andthe trumpet-shaped east portal.

The shotcrete final lining design entailed structuralcomputations, design drawings that depict the lininggeometry, design details and application proceduresalong with a method statements.

Frontier Kemper Constructors, Inc., J.F. Shea, Betonund Monierbau Joint Venture (FKSB) was the con-tractor with Gall Zeidler Consultants, LLC (GZ) astheir design consultants. The Owner was New JerseyTransit and their prime contractor was Washington

Group International. The owner’s project designer wasParsons Brinckeroff, New York.

2 THE CONCEPT

The contract drawings showed a rounded tunnel portalwith a complex geometrical form resulting in three,dimensionally curved sidewalls and roof as well as

Figure 1. Portal structure shotcrete application.

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Figure 2. Waterproofing membrane in mined section.

a trumpet-shaped enlargement for the portal area.For the mined section, the Contract Design specifiedstraight, cast-in-place concrete sidewalls monolithicwith the roof arch.

To optimize flexibility and facilitate tunnel access,the construction method was redesigned in a valueengineering effort. The crews were familiar with theA-frame forms used for the sidewalls in the mined sta-tion sections. Hence, the curved sidewalls for the portalstructure were converted to straight walls comply-ing with the contract’s geometrical dynamic enveloperequirements. For the roof portion, reinforced, high-quality shotcrete was used to form the complex contouroptimized to the existing rock profile. The shotcretereinforcement comprised lattice girders, steel wiremesh for the mined section and rebar reinforcementfor the open cut section. The membrane tunnel water-proofing was extended to the portal face wall to protectthe permanent portal structure against water infiltra-tion. The portal canopy was backfilled with structuralbackfill.

3 VECP PROCESS

The Value Engineering Change Proposal (VECP) pro-cess requires the Contractor to delineate and providethe following specific aspects of their VECP.

• Description of the existing Contract requirementswhich are involved in the proposed change.

• Description of Proposed Changes.• Difference between existing requirements and the

proposed changes, together with advantages anddisadvantages of each.

• Itemization of the Contract requirements whichmust be changed if the VECP is approved.

• Justification for changes in function or characteris-tics of each item and effect of the performance of theend item, as well as on the meeting of requirementscontained in the Mandatory Documents.

• Date or time by which a Change Order adopting theVECP must be issued in order to obtain the max-imum cost reduction including any effects on theProject Schedule.

• Cost estimate for existing Contract requirementscompared to Contractor’s cost estimate of the pro-posed changes.

• Cost of development and implementation by Con-tractor.

4 SHOTCRETE LINING PERFORMANCEREQUIREMENTS

The shotcrete permanent lining generally has to meetthe same criteria in terms of durability, reflectivity andsmoothness as specified in the Contract Design for thecast-in-place concrete lining.

4.1 Reflectivity, maintenance, and ventilation

The shape and evenness of the shotcrete liner in bothradial and longitudinal direction was achieved usinglattice girders and indicator pins (tell tales). For furthercontrol, straight edges were utilized when completingthe finishing shotcrete layer. The surface quality wastypical of state-of-the-art spray-on shotcrete surfacesand current shotcrete lining standard practices.

The shotcrete surface applied in the arch, i.e. gener-ally about 11 feet above the top of rail had little impacton the reflectivity and illumination characteristics ofthe transition sections. Its surface finish will allow forregular maintenance.

Although the surface finish is rougher than a cast-in-place concrete finish (mainly due to the aggregatesize) a negative impact on ventilation performance ofthe tunnel structure was not anticipated, due to the sizerelationship between the tunnel openings and the verysmall increase in the surface roughness. The surfaceand shape qualities of the shotcrete final lining there-fore met project requirements.

4.2 Fire resistance

The Institute for Concrete Technology in Innsbruck,Austria, had recently tested concrete panels with dif-ferent concrete mix designs and under different con-ditions with regard to fire temperature, humidity ofconcrete and loading conditions. Those tests demon-strated that there is no significant difference betweensprayed and poured concrete of the same strength class.Spalling of concrete may reach deep into the concretecross section under severe test conditions. To preventspalling polypropylene (PP) micro fibers were addedto the mix. This observation corresponded with thefindings of other international tests that have beenreported in the literature reviewed in preparation for

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this project. Polypropylenes belonging to the poly-olefin group, which are plastics that are extremelyresistant to chemical and mechanical influences. AsPP only consist of carbon and hydrogen atoms, notoxic substances are created when they are burnedcompletely. Typical PP fibers melt at 150◦C to 160◦C.As a result, the permeability of the concrete with PPfibers is increased in the event of a fire. The addi-tional pore volume created when the PP fibers meltenable moisture vapor produced to be better distributedand escape from the surface. This reduces the risk ofexplosive-like spalling substantially because the con-crete’s permeability is increased in the event of a fire.1

The shotcrete lining design therefore incorporatedthe addition of PP fibers (2.0 lbs/yd3) in the last (inner)four-inch thick layer.

4.3 Shotcrete durability in portal zone

A cement based and epoxy enhanced sealing coat, wasfinally applied in the portal vault section which isexposed to annual temperature fluctuations.

5 STRUCTURAL DESIGN

The basic premise for the structural design was to pro-vide a structurally equal product to that depicted in theContract. A set of loading conditions was developedfrom the computations generated by Parsons Brincker-hoff that formed the basis for the design. The loadingassumption for the lining included the individual loadsas listed below. No independent verification of theseloading assumptions was performed. The structuralcomputations provided in the VECP further detail theload combinations that dictated the case of greatestloading under the assumptions for the liner design.

• Lining dead load,• Rock and rock wedge loads,• Hydrostatic loads,• Grout loads,• Support loads for utilities,• Intermediate construction loads, and• Impact load caused by rock fall.

These load cases and load combinations resulted inlining thicknesses ranging from 12 to 20 inches in thesmallest and widest cross sections respectively. Thestructural reinforcement of the shotcrete liner consistsof two layers of D18 × D18, 6 × 6 welded wire fabricwith additional #3 @ 12′′ longitudinal rebar reinforce-ment in the mined section and 2 layers of #6 @ 6′′longitudinal and #5 @ 6′′ radial, rebar reinforcementin the open cut section.

The shear capacity at the joint between the verticalcast-in-place concrete sidewalls and the shotcrete archwas enhanced by a roughened surface and continuous

shear reinforcement for the outer and inner reinforc-ing layer.

6 QUALITY ASSURANCE

6.1 Shotcrete mix acceptance tests

Apart from the standard compatibility and strength testof the shotcrete mix prior to construction, the shotcretemixes were tested as to their sprayability. A series oftest panels were sprayed using the site equipment toassess the suitability for 100% encapsulation of allreinforcement elements as required for the perma-nent lining. Particular attention was paid to the abilityto fully encapsulating the lattice girder in shotcretewithout voids.

6.2 Pre-construction field trial

Following the successful test series of the shotcretemix, field trials were carried out on standard testpanels 3 feet by 3 feet and 8 inches thick with rein-forcement that simulated field conditions. Vertical andoverhead panels were established. Cores were retrievedand tested in accordance with ASTM. Compressivestrength tests were carried out in accordance with thespecified strength and strength gain requirements. Thetest panels were also saw cut for visual inspection ofcomplete reinforcement encapsulation.

6.3 Nozzlemen qualification

With regard to the shotcrete application, the shotcretenozzlemen experience is a key factor in assuring qual-ity of the shotcrete product. FKSB took the followingmeasures to assure a quality shotcrete application.

Nozzlemen for the project were certified in accor-dance with the guidelines set forth in ACI 506.3R. Twoexaminers, approved by ACI, qualified nozzlemen forinstallation of shotcrete at the project.

Additionally, a procedure was submitted andapproved by the Owner by which a nozzleman maybe qualified by performing field test panels thatdemonstrate his/her ability in performing the work.

In addition to the pre-construction field trials withstandard test panels, a mock-up was constructed thatreplicated the conditions to be encountered in the tun-nel. The entire work cycle from spraying the shotcretethrough the first layer of welded wire fabric againstthe PVC membrane to the application of the finishinglayer with the addition of PP fibers had to be simulatedby this field trial. The test included spraying throughand encapsulating a lattice girder.

Each candidate had to spray a vertical and an over-head panel to demonstrate their skill in shotcreting.Each panel measured at least 30 by 30 inches and8 inches deep and contained reinforcement that simu-lated anticipated field conditions.

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Figure 3. Installation of second layer reinforcement.

Subsequently, the panels were saw cut and observedby the Project Engineer (PB) and two ACI examinerswho provide their observations on quality of the testpanels and recommendations regarding the use of thenozzlemen on the project. Visual inspection examinedreinforcement encapsulation, lack of segregation andproper consolidation.

The examiners consisted of Consultant Mr. GeorgeYoggi and one representative of GZ.

6.4 Testing during construction

Quality control panels were sprayed concurrently withthe shotcrete final lining installation for each 200-cubic yards of material used in the shotcrete lining.Three, core test specimens from three panels wereretrieved and tested in accordance with ASTM C 42.

7 LOCATIONS OF APPLICATION

The VECP was intended to be installed in two areas ofthe structure:

• the “mined tunnel section”• the “open cut section”.

Approximately 130 feet of mined tunnel was equip-ped with lattice girders and a final shotcrete lining.Theopen cut section extends approximately 30 feet outsidethe rock portal. Widening of the tunnel cross sectioncommenced within the mined section. The overall tun-nel height and width was increased in a smooth tran-sition from the running tunnel size to the maximumheight of approximately 23 feet and 55 feet width.

The thickness, reinforcement and height of the ver-tical cast-in-place concrete sidewalls in the mined sec-tion remained as per the Contract Design. In the opencut section, the concave sidewalls, as specified in theContract Design, were replaced by vertical, cast-in-place concrete walls.

The construction of the shotcrete permanent lin-ing within the mined section was completed prior toconstruction of the portal structure in the open cut.

8 PREPARATIONS PRIOR TO SHOTCRETELINING INSTALLATION

8.1 Mined section

Upon completion of the excavation and initial rocksupport installation, a smoothening layer of shotcretewas installed to prepare the substrate for waterproof-ing system installation. As defined in the ContractDesign, the waterproofing system consisted of a geo-textile layer and a PVC waterproof membrane. Thesidewall drainage, footings and cast-in-place concretewalls were constructed as specified in the ContractDesign.

In order to enhance the shear capacity in the inter-face between the cast-in-place concrete wall and theshotcrete lined arch structure, the concrete surface wasroughened by power wash facilities (green cut) andreinforcement spanning the interface was provided.

In accordance with the Contract Design, the water-proofing system was installed against the shotcretesmoothing layer around the tunnel arch. BA-Anchorswere used to secure in place the reinforcement for theshotcrete permanent lining. Grout hoses were installedin the longitudinal tunnel direction to serve as grout-ing ports for the contact grouting after completion ofthe shotcrete lining installation.

8.2 Open cut section

In order to avoid unnecessary excavation and demol-ishing work, the existing stone walls in the portal areawere left in place to the extent they did not infringe onthe clearance required to construct the new structure.Up to the crown elevation of the vertical sidewalls cast,drainage concrete was installed to provide enhancedcapacities for draining any run-off surface water andfissure water from the rock face at the portal. Ductbanks, drain lines and walkways remained as definedin the Contract Design.

Following the footing and drainage concrete instal-lation, the vertical cast-in-place concrete walls wereconstructed. Between the drainage (popcorn) concreteand the vertical concrete wall, the waterproofing sys-tem as described above was installed. Similar interfacedetails between the concrete walls and the shotcretearch were installed as described for the mined section.

8.3 Reinforcement installation

8.3.1 Mined sectionFollowing the erection of the vertical cast-in-placeconcrete sidewalls, the first (outer) layer of the D18 ×D18, 6 × 6 welded wire fabric and rebar reinforcement

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Figure 4. Reinforcement installation in the open cutsection.

was installed. Lattice girders on 5-feet centers wereerected founded on adjustable footplates mounted ontop of the concrete sidewalls. Tie-bolts and steel spi-ders were attached to the BA-Anchors to secure thewire mesh and lattice girders in place during shotcret-ing. Tie wires were mounted at the first layer of meshreinforcement in preparation for fixing the secondmesh layer at a later stage.

8.3.2 Open cut sectionUpon completion of the sidewall construction, theouter layer of the bar reinforcement and the lattice gird-ers were erected on 5-foot centers. Temporary supportto the steel reinforcement was provided by tie-backrock dowels installed in the rock portal face wall andauxiliary rebars installed in longitudinal and radialdirection. To facilitate shotcrete installation, expandedmetal sheets were installed on the extrados side of theportal structure. The expanded metal sheets were cov-ered with a shotcrete smoothening layer at a later stageto prepare for the installation of the waterproofingsystem on the outside of the portal structure.

An expansion joint element was previously installedand anchored in the shotcrete lining for the minedsection to form the interface to the open cut section.

9 SHOTCRETE APPLICATIONPROCEDURES

The application of shotcrete was carried out utiliz-ing robotic spraying equipment operated by trainedpersonnel. Experienced, skilled supervision ensureduniform application that resulted in the shotcrete liningquality in accordance with the project requirements.High quality wet-mix shotcrete was employed.

Shotcrete was applied in a series of stages where thereinforcement members were progressively encased,thus preventing the spraying through multiple lay-ers of reinforcement and avoiding shadowing. Thefirst shotcrete layer was applied against the water-proofing membrane and the outer reinforcing layerof welded wire fabric. The welded wire fabric facil-itated the application of the shotcrete against themembrane and provided a supporting mechanism forthe wet shotcrete. The subsequent shotcrete applica-tion to the full design thickness was carried out insubsequent steps that were executed within a timeframe not exceeding seventy-two (72) hours. Thissequence resulted in an overall continuous shotcreteapplication.

Preparations for and the shotcrete application werecarried out in accordance to a procedure defined dur-ing the VECP design phase. The procedure entailedamong others the following check steps:

• Spray area, check if additional deck-chairs arerequired to avoid sagging of the waterproofingmembrane

• Availability of lifting devices• Availability and working condition of robotic spray-

ing equipment and pumps• Availability and condition of accelerator• Illumination of work area• Adequate protection of concrete sidewalls• Shotcrete order and delivery, time, temperatures• Slump test of each delivery• Retardation of shotcrete, if necessary.

9.1 Shotcrete application in the mined section

9.1.1 Application of first shotcrete layer (plainshotcrete)

The constant shotcrete spray was applied from thebottom of the haunch proceeding to a maximum of5 lattice girder bays and repeated on the opposite side.Following that, shotcrete was placed along the latticegirders in an alternating sequence on both sides of thetunnel until the lattice girder was encased in shotcreteover the entire arch length. Excess shotcrete was thenremoved from the intrados bar of the lattice girders.

If required, additional deck chairs were mountedbehind the exposed mesh reinforcement to strap backany sagging part of the waterproofing membrane.Following that, the bays between the girders were filled

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Figure 5. Installation of second layer reinforcement in theopen cut section.

with shotcrete, starting from haunch up to the top oftunnel in alternating sequences from both sides of thetunnel.

9.1.2 Installation of the second layer ofreinforcement

The second layer of mesh was fixed on to the tie wirespreviously placed and protruding from the shotcretesurface. Thickness indication pins were installed in thefirst shotcrete layer to ensure the required thickness ofthe second shotcrete layer to be installed following thewire mesh installation.

Surveying was used to process data and mark out theneat line. A #3 bar, radially installed on the indicatorpins was used to set out the required shape and profilefor the second shotcrete layer.

9.1.3 Intermediate shotcrete layersThe shotcrete surface forming the substrate for the sub-sequent shotcrete application was cleaned using powerwash facilities. Second shotcrete layer.

Shotcrete was applied along the previously installedprofile indicator bars. Upon completion, the pins andindicator bars were cut and removed. Using powerwash facilities, the substrate for the shotcrete appli-cation in the bays between the previously installedshotcrete stripes was prepared. The panels were thenfilled with shotcrete using the previously installedshotcrete strips for thickness guidance.

9.1.4 Final shotcrete layerTo ensure adequate tunnel profile of the final prod-uct, studs mounted on the lattice girders were used forthickness and shape guidance.

PP fibers were added to the mix for the final layerof shotcrete to enhance the fire resistance and spallingbehavior of the shotcrete. The final layer is approxi-mately 4 inches thick.

9.1.5 Contact groutingAfter the shotcrete reached the design strength of4,000 psi, contact grouting using cementitious groutwas carried out to establish a near voidless contactbetween the shotcrete final lining, the waterproofingsystem and the initial shotcrete tunnel support. Tofacilitate the contact grouting, and ensure the fillingof voids, grout hoses were attached to the waterproof-ing membrane prior to the initial mesh and shotcreteinstallation.

9.2 Shotcrete application in the open cut section

The checking and application procedures implementedprior to and during the installation of the shotcrete inthe open cut were generally similar to those employedfor the mined section.

Upon completion of the first shotcrete layer, thick-ness indicators, cleaning measures and the secondlayer of rebar reinforcement was applied in a proceduresimilar as described for the mined section.

After completion of the final shotcrete layer, a thincement based sealant layer was applied to enhanceconcrete durability under variable climate conditions.

On top of the shotcrete canopy, a smootheningshotcrete layer was installed covering the expandedmetal sheets to prepare for the waterproofing systeminstallation.

Upon completion of the construction of the shot-crete canopy, the portal head wall was constructed andconnected with reinforcement to the shotcrete canopy.

The waterproofing system previously installed inthe sidewall areas was continued over the roof of theshotcrete canopy. A protection layer was installed toprotect the waterproofing system from damage duringsubsequent backfilling of the portal.

10 ATTACHMENTS TO THE SHOTCRETEFINAL LINING

Generally, the attachments to the shotcrete final liningfor utilities were carried out as per the Contract Designas far as minor loads are concerned. Typically, expan-sion anchors were used for this purpose. In cases wherehigher loads had to be supported such as the catenarysystem, attachments and local reinforcing elements(inserts or “spiders”) were provided and installed aspart of the reinforcement of the shotcrete and weresprayed in along with the build-up of the shotcretelining section.

11 SUMMARY

Table 1 summarizes the basic dimensions, lining thick-nesses, reinforcement as applicable to the VECPsections of the Weehawken Tunnels.

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Figure 6. Shotcrete application.

Table 1. Summary of basic dimensions.

SectionLength Width Height Thickness Reinforcement

Mined 2 28′-0′′ 17′-4′′ 12′′ 2 layers WWF57′-10′′ D18 × D18, 6 × 6,

#3 rebars @ 12′′Lattice Girders @ 5′

Mined 1 28′-0′′ 17′-4′′ 12′′ to 2 layers WWF71′-2′′ to to 16′′ D18 × D18, 6 × 6

37′-9′′ 23′-5′′ Lattice Girders @ 5′Open Cut 37′-9′′ 23′-5′′ 20′′ #6 @ 6′′

27′-9′′ to longitudinal55′-4′′ #5 @ 6′′ radial,

2 layers

12 CONCLUSIONS

The use of the cast-in-place concrete sidewalls incombination with high quality shotcrete to form thecomplex transition geometry proved to be successfulat the Weehawken Tunnels Project.

The timely completion in accordance with theContract quality requirements demonstrate that acombination of traditional and modern constructiontechniques can provide state-state-of-the-art solutionsto challenging project requirements.

Figure 7. Completed portal structure.

ACKNOWLEDGEMENTS

The authors wish to thank all parties involved in thedesign development and approval as well as execu-tion process for the positive contributions and support.New Jersey Transit Corporation and their prime con-tractor Washington Group International were instru-mental in the process of preparation and acceptance ofthe Value Engineering. The project designer ParsonsBrinckerhoff, NY was supportive to the alternativeconcept.

The contribution of all individuals involved inthe VE from development to final completion isappreciated.

New Jersey Transit has not endorsed this paper.The contents are for informational and educationalpurposes only.

REFERENCE

1. Brux, G.: Fire Resistant Shotcrete in the Gotthard BaseTunnel. Tunnel 5/2005.

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