one-pass segmental lining in a corrosive environment

Proceedings of the World Tunnel Congress 2014 – Tunnels for a better Life. Foz do Iguaçu, Brazil.

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1 INTRODUCTION

In order to achieve durable concretestructures with high expectations on usability,especially for application in sewerage systemsas the construction of conveyance interceptorsand connected ducts, the use of corrosionresistant materials for covering the internalsurface area is increasingly important. Thispaper discusses differences betweenconventional plastic one-pass lining materialsand Combisegments®, their practicabilityduring segment manufacturing and tunneling,completed by experiences of case experiencesusing conventional liners.

Mechanized tunneling with segmental liningand increased demands on structural surfaceprotection can be implemented either in one ortwo passes. In contrast to two-pass systems,one-pass segmental lining directly combinesstatic requirements of the tunnel structure aswell as final protection and improvement ofconcrete surfaces by using reinforced precastsegments with embedded plastic liners.

Significant differences exist betweendifferent available mechanical anchored liningmaterials in terms of used thermoplastic resin,integrated anchoring type, its shape andalignment. In addition, varieties between thedenotation of one-pass segmental lining, relatedexpectations and practical tunneling issues exist.Thus, this paper examine whether centralprospects, such as a simplified segmentmanufacturing and tunnel construction withoutadditional requirements to achieve concreteprotection, can be fulfilled comprehensive byusing conventional lining solutions.

In contrast, Combisegments® combinesstandard reinforced segments with a framedliner made of Telene®-pDCPD(polydiclopentadiene), incorporating severalcustom-made elements. Manufacturing can takeplace without additional expenditure and issimplified due to an already integrated gasketframe.

One-pass Segmental Lining in a Corrosive Environment

J. RiechersHerrenknecht Formwork Technology GmbH, Schwanau, Germany.

G. RecherTelene SAS, Bondues, France.

S. AllainTelene SAS, Bondues, France.

ABSTRACT: Tunnels constructed for the purpose of discharging waste water as well as forpreventing wet-weather overflows by intermediate storage are particularly exposed to internalcorrosion due to sulfuric acid attacks. The awareness of the internal corrosive environment has beenincreased by rising expectations regarding life span, which in turn led to higher requirements onprotective lining materials for application in concrete tunnels. This paper will focus one-passsegmental lining which enables the integration of a corrosion resistant liner during the castingprocess of reinforced segments. Based on a brief discussion on different mechanical anchored liningmaterials, this paper summarizes their usability in concrete moulds and handling on the job-sitebased on case experiences. The findings will be compared with a new one-pass segmental liningsolution which differs considerably from other systems.


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2 CONVENTIONAL SEGMENTAL LININGIN ONE PASS

Mechanized tunneling with segmental liningcan be implemented either in one or two passes.Two-pass systems divide the tunnel constructionin two independent phases. Subsequent to theinitial tunnel construction with conventionalprecast segments a corrosion resistant layer isinstalled by using cast in situ methods (cast inplace concrete lining), different lining materialsor pipes. This support and protection system canbe as well executed by means of temporaryreinforced shotcrete and using formworks forcreating the final concrete lining.

In contrast, one-pass segmental liningdirectly combines functions as static bracingand final lining by using reinforced precastsegments with directly embedded thermoplasticliners on its interior surface and, on demand, aswell on its outer surface. Existing conventionalconcrete embedded liners are also known asmembranes and corrosion protection liners(CPL) (Chapman et al., 2005; Kaneshiro et al.,2011).

More than 60 years ago, after Kaneshiro etal. (2011), first tunnels have been constructedwith precast segments in accordance with theinitial thought of a one-pass system.Accordingly, the concrete structure itself hasbeen used as a permanent surface exposed todischarged fluids and emitted gases.

Based on considerably recognized corrosionproblems, especially in sewers, the importanceof concrete protection, and thus durablesewerage infrastructures, continues to increase.Especially, sewers constructed in warmerclimates indicate a higher risk potential forcorrosion, resulting in an accelerated growth ofmycobacterials (Chapman et al., 2005).

In addition, worldwide increasing levels ofenvironmental awareness and growingrequirements/- costs for wastewater treatment,lead to another focus - exfiltration andinfiltration (seepage). The absence of exfil-tration of wastewater secures both adjacent soiland groundwater tables. On the other hand,water tightness and avoidance of seepageentering the sewage, whereby the amount ofwastewater to be treated is not increased, lead tocost savings for treatment plant operators.

On closer examination of the denotation ofone-pass segmental lining with CPL inaccordance with practical tunneling issues,however, it becomes apparent that central

expectations, e.g. accelerated/ - simplifiedsegment manufacturing and tunnel constructionas well as the prevention of sulphide corrosion,cannot be fulfilled comprehensive by usingconventional thermoplastic lining solutions.

To be precise, usual lining sheets embeddedin concrete structure of segments indicate eitherone or two overlaps (radial and/ orcircumferential) or are adapted to specificsegment dimensions with resulting open jointsafter ring assembly (Riechers, 2013). Thus,subsequent effort arise for sealing of radial andcircumferential joints either by using differentwelding methods with/ without welding strips orplacing e.g. caulking grooves (Figure 1).

Figure 1. Examples of weldings: butt welding [left], heatfusion using welding strip and liner overlap [right]

(Riechers, 2013).

In summary, commonly used definition one-pass/ one-step lining refers merely to the ringassembly during tunneling by means of a TBMerector. Required work for sealing/ welding ofall seams and openings for tunneling accessoriesindicate a second step, usually hidden atintroduction of conventional one-pass CPLs.

Potential long-term risks are present due toinfiltration or exfiltration with environmentalimpacts as a result of incorrect welding. In thiscontext, Kaneshiro et al. (2011) pointed out thatvarious types of liners embedded in precastsegments indicate drawbacks from a cost andconstruction point of view due to completioneffort after ring assembly with significant addedcost for installation and testing.

Furthermore, hydrogen sulphide (H2S), adecomposition product of organic sewagecontents and resulting gases can penetratethrough unsealed areas, followed by settlementsand sulphuric corrosion (Carroll et al. 2010).


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2.1 Lining materialsConventional lining materials are usually

manufactured from various plastics likepolyvinylchloride (PVC), polyethylene (PE) orhigh density polyethylene (HDPE). Dependingon the manufacturer, different anchoringsystems as knobs, rips or bridged crossed areintegrated in order to achieve concrete bond.Such systems, after Carroll et al. (2010), havebeen introduced to applications in concretestructures since 1940s. Production-wise, linerropes are rolled or cut into pieces of certaindimensions depending on customerrequirements. The later task is usually carriedout on-site just before placing into the concretemould, preventing dimensional deviations dueto different coefficients of expansion.

Although significant differences exist indetails, all conventional liners as well asCombisegments®, introduced in section 3, offerlogistic advantages compared to precast pipesused for internal tunnel protection. Especially,for tunnels with diameters larger than3.6 m (12 ft), transportation difficulties (passunder bridges, narrow curves, etc.) lead toincreased costs.

Mechanical properties as adhesive tensilestrength or hydraulic backpressure resistance ofliners embedded in precast segments depends,apart from the concrete mixture, both on anchorshape, size, orientation and on sufficienthandling in concrete moulds during segmentmanufacturing. Furthermore, elasticity andmaterial thickness of the initial liners affect thebehaviour of the system, e.g. either prevent oreven favor damages by liner bubbling (Riechers,2013).

3 COMBISEGMENTS®

Herrenknecht AG and HerrenknechtFormwork Technology GmbH, an independentsubsidiary of Herrenknecht AG, supported byTelene SAS, a French subsidiary of ZeonCorporation, developed Combisegments®.

The designation Combisegments® describesa structural composition consisting of acommon ferroconcrete segment incorporating aframed corrosion resistant lining element.Combisegments® is applicable for segmentallining applications with tunnel diameters largerthan approximately 2 m (6 ft).

However, limitation is attributable todemands on working space using a TBM, i.e.segment erection.

A Combisegments® lining element consistsof a Telene®-pDCPD framed liner,approximately ~ 4 mm (5/32 ”) in thickness,including several functional elements: An EPDM gasket which is mechanically

integrated into the surrounding liner frame. A long-lasting anchoring structure on the

back side of the liner to ensure connectionwith the later casted concrete.

If requested, typical accessories as socketsfor segment handling by erector pins ordowels for subsequent mounting.

All these elements are integrated togetherduring the one step reaction injection mouldingprocess used to manufacture theCombisegments® lining element. The EPDMgasket frame is mechanically integrated into thesurrounding liner frame and thus positioned in aforce locking manner at tunnel’s interior. This isa considerable difference from conventionalconcrete segments framed with EPDM sealingswhich are connected to concrete surface eitherby means of adhesive or anchored with smallwings in the concrete surface layer. In addition,a long-lasting anchoring structure is integratedon the back of the liner to achieve concrete bond(cf. section 3.1).

Although the concept of Combisegments® isrelatively new, use of pDCPD as a concretelining material for tunnel applications is welldeveloped in Japan since 1995 and applied at 12known sewer and water tunnel projects (JapanInstitute of Wastewater EngineeringTechnology). Figure 2 shows an irrigationtunnel with dimensions of 3.5 m (11.5 ft) ID xapprox. 2,042 m (6,700 ft), constructed from2012-2013 in Nagoya, Japan.

pDCPD is known for its durability andchemical resistance in many harshenvironments, making it a material of choice inthe field of chlorine production, as well as insulphuric acid media electrolysis process.Resistance against critical corrosive media suchas sulfuric acid, hydrogen peroxide or sodiumhydroxide at high concentration and temperaturehas been extensively evaluated (Telene®pDCPD chemical resistance). Furthermorechemical resistance of pDCPD liner has beenevaluated by IKT according to DIBt principlesin comparison to PE-HD (IKT, 2013).


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Figure 2. Irrigation Tunnel with pDCPD liners embeddedin segments. Nagoya, Japan, March 2013.

Combisegments® enables sealing of radialand circumferential joint zones through thetunneling process itself and positioning of thekey stone at each ring. By the way, TBMerectors can handle Combisegments® by meansof a mechanical pin connection, but as well witha vacuum lifter. As a result of simultaneousgasket compression of neighbouringCombisegments® a force locking unit isformed. The obtained tightness of joint areasand absence of leakage paths ensures as welllong-term protection of concrete structuresagainst sulfuric corrosion by aggressive wastewater and emitted gases (Figure 3).

Figure 3. Combisegments® lining element: compressedgasket after placement of the key segment.

The lining system, however, requires both adurable and robust liner and a concreteanchoring system. Together, the lining solution

must be able to withstand hydraulic heads as aresult of infiltrating groundwater by concretepermeability, possible arising concrete cracks orbetween segment contact surfaces.

3.1 Concrete bond and backpressure resistanceA long-lasting concrete bond is particular

important, independent of the respective initiallining material. In addition the liner itself mustbe durable and requires a certain thickness andstiffness in order to prevent bubbling effects e.g.as a result of hydraulic loads. Liner andanchoring structure must form a harmonizedcomposite element by pouring concrete and thuscreating the final Combisegments® in themould.

T-shaped PVC liners, for example, werechosen for the Panama Wastewater Interceptorin Panama City, after Wilshusen et al. (2012),and the Upper Northwest Interceptor inSacramento, after Kaneshiro et al. (2011) had athickness of 1.65 mm (0.065 in) respectively1.75 mm (0.069 in) at the latter one. Thereduced material thickness in itself indicateslow liner stiffness, which lead to potential risksof damages during segment fabrication,tunneling and sewer operation. Unlike t-shapedanchors, the PVC liner, after Kaneshiro et al.(2011) is not able to withstand significantpressure without causing balloon effects.Combisegments® lining elements, however,indicates comparatively high inherent stiffness.

In order to achieve concrete bond and long-term hydraulic back pressure resistance,Combisegments® lining elements are equippedwith a honeycombed (HC) anchoring layermade of PP polymer covered on one side by anEthylene copolymer-film. The HC system isintegrated by chemical welding of thecopolymer film to pDCPD during themanufacturing process of making theCombisegments® lining element (Recher et al.,2013).

The HC layer presents a considerable numberof small undercuts on the open end of the cellslocked into the concrete structure, which in turnenables sufficient pull-off resistance by forminga large anchoring surface area. Basically, thehigher the adhesion between concrete and thesurface structure of the designed anchoringstructure the stronger the bond between linersheet and concrete. Consequently, in order toachieve best possible values a suitableanchoring shape must be selected to achieve the


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largest possible contact surface to the concretemixture. Figure 4 shows a top view of thehoneycomb before integration in theCombisegments® lining element.

Figure 4. Picture of a HC 8 honeycomb top view [left]and core drilling of a Combisegemts® sample [right].

Referred to implemented pull-off tests inaccordance with DiBT test standards an averagepull-off strength of 1.1 N/mm2 (1.1 MPa), equalto a hydrostatic head of approx. 110 m (360 ft),was determined (Riechers, 2013). On request,by variation of cell thickness and diameter, thehoneycomb anchoring structure can beoptimized to obtain the maximum bondingstrength between the liner and the variousconcrete types.

3.1.1 Theoretical calculationAn attempt was made to approach by simple

calculation the predicted pull-off force that onecan expect from a specific type of honeycombanchoring system and anticipate potentialcontribution of geometry variation. Atheoretical model was developed to approachthe desired bonding strength between the linerand the concrete.

As with other concepts for plastic liner,concrete/ liner connection is obtained throughundercuts protruding from the plastic linerssurface that are embedded into the castedconcrete. After concrete hardening the undercutsare anchored into the solid concrete casting.

Two interfaces have to be considered: One islocated between the concrete and the anchors;this interface is only linked to the geometry ofthe anchor as concrete is not adhering on mostof the thermoplastic. The second interface isbetween the flat liner surface and the anchors.The strength of this interface is linked to the

geometry of the connection, its quality and thestress at yield value of the plastic polymerconstituting it. In the case of the honeycombanchoring layer of a Combisegments® liningelement, this second interface is achieve via achemical welding of the honeycomb to theTelene®-pDCPD liner during the lining elementfabrication. The weakest interface will be thearea where delaminating will take place.

3.1.2 Interface between anchors and concreteIn the case of the Combisegments®

honeycomb anchoring layer the evaluation isdone by first measuring the projected undercutsurface assuming that the pull-off direction isperpendicular to the liner surface. The ratio ofthis undercut surface to the liner surface willgive a first indication of the potential connectionstrength with the concrete. Figure 5 andFigure 6 show magnified view of thehoneycomb top view and wall section.

Figure 5. Anchoring width dimension of HC 8honeycomb.

Anchoring surface per honeycomb cell isthen obtained by multiplying the wall length ofa cell by the anchoring minus cell wall thicknesswidth divided by 2.

Figure 6. Section of a honeycomb cell showing the T-shape created on the top of the cell


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Table 1 below summarise the dimensions of2 honeycombs used in Combisegments® liningelements.

Table 1.Dimensions of honeycombs used inCombisegments®

Type Cell

Cell wallthickness

Anchoringwidth

HC 8 8 0.5 ~1.5HC 16 16 0.5 ~1.5All dimensions are in mm.

The total anchoring surface per surface unitis then calculated as shown in Table 2:

Table 2.Undercut anchoring surface of HC 8 and HC16per m² of liner.

Type Cellareamm²

Cell perimeter

mm

Number ofcell/ m²

Undercutsurfacemm²/m²

HC 8 42 24 24 056 288 675HC 16 166 48 6 014 144 338

3.1.3 Interface between liner surface andanchoring system

In a similar way the surface contact betweenthe honeycomb wall and the liner – in otherwords the welded area - is evaluated in Table 3.

Table 3.Surface contact between HC anchoring layer andliner surface per m² of liner

Type Cell perimeter

mm

Number ofcells/ m²

Contactsurfacemm²/m²

HC 8 24 24 056 144 338HC 16 48 6 014 72 169

3.1.4 Evaluation of the theoretical pull-offforce

Once the interface surfaces have beencalculated it is relatively simple to calculate thecorresponding pull-off force. The maximumpull-off force taken by the interface is the resultof the undercut anchoring surface times theconcrete strength in first case, and the result ofthe connecting surface times the anchoringmaterial strength in the second one.

A class C45/55 concrete (45 N/mm2

compressive strength after aging) was con-sidered for the calculation.

The tensile strength of the concrete was takenat 15% of the compressive strength or6.75 N/mm² (University of Memphis). Thetested ethylene copolymer-film covering thehoneycomb has strength of 8 N/mm². Theresulting pull-of forces are presented in Table 4.

Table 4.Evaluation of pull-out force for HC8 and HC16honeycomb anchoring layer

Type Undercutsurfacemm²/m²

Contactsurfacemm²/m²

Concreteto HC

strengthN/mm²

HC toliner

strengthN/mm²

HC 8 317 543 144 338 2.14 1.15HC 16 158 771 72 169 1.07 0.58

The resulting values should be taken asevaluations only as multiple factors have notbeen considered in this approach. Nevertheless,implemented pull-off by tests by IKT on 1:1scale Combisegments® sample indicatedcomparable values on tensile strength, seesection 3.1. It is particular important to useconcrete moulds with sufficient distribution ofvibration energy in order to achieve an evenlyhoneycomb cell filling with concrete.

3.2 Hydraulic backpressure resistanceInvestigations on hydraulic backpressure

resistance can be either implemented onrectangular concrete specimens with embeddedliners or in one-to-one scale on precast segmentswith natural bending. Based on the testimportance and transferability of results to realtunnel conditions, Herrenknecht Formworkdecided to consider latter option for test atGerman Institute for Underground Infrastructure(IKT). A practical-orientated long-term test hasbeen conducted on three trapezoid precastCombisegments® with a thickness of 135 mm(5.3 in) and length of 750 mm (29.5 in) inaccordance with German DIBt test standards forselection of suitable sewer linings. By the way,segments with identical dimensions have beenused in 2011 for construction of the InterceptorSewer Río Nalón, a segmental lined tunnel withan internal diameter of 2.0 m (6.5 ft).

Prior to the test execution, at each segmentsix water channels are drilled using a cone bit(Ø 3/4”) up to the casted in reverse side of theliner.

Drillings are evenly distributed around theembedded socket in the center of Combi-segments® samples. After installation of hoses


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for hydraulic pressure application, waterchannels are sealed using adhesive on theconcrete transition zone (Figure 7).

Figure 7. Hydraulic backpressure resistance: connectedsegment [left], detail on water hose arrangement [right],

(IKT, 2013).

Under surveillance of a pressure regulator, awater pressure of 1.5 bar (0.15 MPa) over aperiod of 1,000 h (≈ 42 days) has been appliedwithout cracks and delamination of theCombisegments® lining element from theconcrete body. Subsequent to this first long-term test, the hydraulic pressure has beenincreased in five steps of 30 minutes each up to6 bar (0.6 MPa). The pressure increase has beenstopped by reaching the pressure limit of usedtesting facilities. All tests could be successfullycompleted without any sign of failure on eachtested Combisegments® sample, which is inturn due to an efficient HC cell backfilling withconcrete.

3.3 Ability for repairDuring segment production and subsequent

handling and installation of Combisegments®surface damage can occur on lined side ofCombisegments® despite the high impactresistance of the Telene®-pDCPD liningmaterial. Those damages can be limited tosurface scratches in the lining material or goingdeeper into the anchoring system to eventuallythe concrete itself. Thus, it is important to knowrepair possibilities, recommended material andas well the way of implementation.

In the case of surface damages conventionalepoxy based repairing materials are used, eithermixed and applied with a spatula or using a bi-component mixing cartridge (Figure 8).

Figure 8. Repair of Combisegments® liner surface(Recher et al., 2013).

In the case of the damage reaching thehoneycomb or the underneath concrete thedamage area is enlarged using e.g. a pneumaticgrinder to a square or rectangular area, on adepth of at least 20 mm (0.8 in). A patch ofCombisegments® liner is cut to fit in theenlarged damage area leaving 2 to 5 mm (0.08-0.2 in) along the edge and put in place usingrepair mortar like SikaTop®-121 or SikaTop®-122HB generously applied on both sides(Figure 9).

Figure 9. Repair of Combisegments® lining element:Patch [left], patch covered with repair mortar[middle],

enlarged damage ready to receive patch [right],(Recher et al., 2013).

After leveling the patch to the liner surfaceand cleaning the excess of repair mortarescaping from the edge, the repair mortar isallowed to dry before repairing the edge gapusing an epoxy base repairing material, afterRecher et al., (2013).


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3.4 Project experienceBased on a long history of corrosion

protective liners in the wastewater market, linersdirectly embedded in precast segments arecomparatively new but becoming moreimportant due to economic advantages.

Recognized projects as the Upper NorthwestInterceptor(UNWI) (ID 3.6 m (12 ft)) inSacramento or the Panama Interceptorexcavated in Panama City (ID 3 m (10 ft)), forinstance, have been constructed using theconventional one-pass segmental liningapproach with embedded PVC liners(Wilshusen et al., 2012; Hargreaves et al.,2011). Although both projects were successfullyfinished significant differences in construction/lining quality became noticeable and togetherboth reference projects highlight key differencesbetween conventional CPLs and Combi-segments®.

3.4.1 Segment manufacturingCompared to ordinary segment manu-

facturing, first of all, the conventional linersheet must be laid on the bottom of the concretemould after thorough cleaning of the surface.Generally, the liner and protruding overlapsmust be fixed precisely on the bottom, i.e. bymechanical adjustable mould shutters.Furthermore, liner openings for integration ofe.g. grout holes and erector sockets for segmenthandling must be produced by cuttings inadvance. Placing of additional segmentequipment as the reinforcement cage, sockets,plastic connectors or dowels takes placeafterwards followed by pouring concrete.

At both projects, after concrete curing anddemoulding, required gasket frames weremanually installed in the sealing groove of theconcrete surface using adhesive (Wilshusen etal., 2012; Hargreaves et al., 2011). This resultsin a significant additional expenditure.

Due to distorted lining sheets during castings,after few months up to 6.8 % of casted segmentswere damaged and this led to increased cost forsegment repair and decreased production rates atthe Panama Interceptor Project (Wilshusen etal., 2012). He furthermore stated that still in thelast four month of production 0.7 % ofmanufactured segments were damaged, despiteincreased effort for e.g. controlling the concreteslump, increased sidewall calibrations and

replacement of perimeter rubber bevels atmoulds.

Figure 10. Typical appearance of hollow spaces underPVC lining (Herrenknecht, 2011).

In contrast to thin and pliable PVC sheetswith reduced rigidity, Combisegments® liningelements are itself stable and offer advantages interms of quality and costs. This is attributable tothe fact that:a) the gasket is already integrated into the

lining element, i.e. gluing of gasket frameson cured segments or complicated fixationof concrete embedded gaskets withinconcrete moulds is no longer required;

b) Combisegments® lining elements must besimply placed centered on the mouldbottom, mechanical fixed by means of acustomized groove system in the shutters ofCombisegments®-moulds.

Figure 11. Handling demonstration withCombisegments®-mould (ID 2,000 mm).


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3.4.2 Tunneling and completionThe main drawback of conventional

segmental liners is the presence of unavoidableradial and circumferencial joints and theresulting completion effort by welding andsparks testing (cf. also Chapman, 2002).Welding can be carried out during or aftertunneling, either by means of robotic equipmentfor large tunnel diameters, respectivelysubsequent to main excavation job, or by usingmanual tools at small ones. Generally, theshortage of available working space at the TBMand backup increases with decreasing internaltunnel diameter. The lower the space betweenTBM and tunnel interior surface, the higher isthe risk of harmful effect on liner surface due todebris and remnants in between.

It is not possible to state in general that allrequired joint weldings can be executed duringtunneling from the TBM within the remainingtransition zone or in a working located betweensegment erector and operator cabin. Although aTBM is designed for this purpose, unsealedareas, e.g. below and alongside of rails andfastenings for supply lines, cannot be protected/sealed before dismantling TBM installations. Inaddition, if the working area is not keptthoroughly clean, the weldings are hinderedanyway or the lining can be damaged by theadvance movement itself. Project reports ofUNWI and Panama Interceptor refer inconformity that additional respectivelyremaining joint weldings up to ¼ of the tunnelperimeter (e.g. invert area) at the PanamaProject could only be realized after cleaning anddismantling of tunneling installations(Hargreaves et al., 2011;Wilshusen et al., 2012).

For the entire UNWI project over 122 km(400,000 ft), after Hargreaves et al. (2013), ofT-lock joints were welded and spark tested.Human errors during welding and testing cannotbe excluded totally, and thus long-term risk bycorrosion influence along all seams may exist.

The Panama Interceptor Project has provedas very complicated in terms of handling ofprecast segments and cleanness duringtunneling. In this context, several damages toliners and visible delamination effects wereattributable to e.g. muck fragments, fallen fromthe conveyor belt in the path of rubber wheelsand fault liner overlaps in the opposite directionof advance drive (Wilshusen, 2012;Herrenknecht, 2011).

Internal construction reports of HerrenknechtAG support statements that PVC T-Lock sheetswere extremely soft and pliable, which in turnhas led to remaining problems even withoutoverlaps due mud removals pushed underneaththe liner during tunneling. In addition, laborersdid not follow instruction to keep job-site cleanas much as possible in order to prevent furtherdamages to the liner. By way of an example,Figure 12 shows results of careless dischargeditems by the welders and mud. Unfortunately,such occurrences always led to damages tosome rings until the damage got visible afterTBM advance movement.

Figure 12. Unclean area under the segment feeder: mud, acan and remnants of truncated PVC liners

(Herrenknecht, 2011).

In addition, executed weldings had often ledto deformation and bulging of welded overlaps,which is attributable to thermal material stressesin this area (Herrenknecht, 2011). Keydifferences between conventional CPLs andCombisegments® are summarized by means ofthe following visual comparison.

Figure 13. Summarizing comparison of usability.


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4 CONCLUSION

By industrializing sealing operation andaccessories placement Combisegments®concept overcomes some of the majordisadvantaged of conventional corrosionprotective liners embedded in segments andoffers full benefit of a true one-pass segmentallining. Not only replacing the welding orcaulking operations inherent to conventionallining by fully gasket integrated in the framedliner, Combisegments® also reduce the time toservice of the tunnel project. Consequently, timeconsuming post-sealing operation is done duringthe manufacturing of the Combisegments®liner, taking place in parallel with segmentmould manufacturing and TBM engineeringprocess. Lining and segment quality can becontrolled in an easy access open environment.The final installation by TMB erector is lesscomplicated and susceptible to liner damages.

Combisegments® offers long-term corrosionprotection, specially adapted to projectrequirements and dimensions of segments.Combisegments® lining elements can bedelivered worldwide, after undergoing internalquality checks, just-in-time in accordance to thesegment manufacturing schedule.

REFERENCES

Hargreaves, A. ; Chandler, T. ; Kazi, P. ; Ward-McNally, I. and Dean, A. 2011. Construction of theUNWI 1&2 Tunnel-Sacramento, California. In:Proceedings of the Rapid Excavation and TunnelingConference 2011. Englewood, Colorado, USA:Society for Mining, Metallurgy, and Exploration, Inc.(SME). p.1003-1019.

Carroll, J.B. and Ivory, H.M. 2010. Corrosion ProtectedSystems for Tunnels and Underground Structures. In:Proceedings of the North American TunnelingConference 2010. Portland, Oregon, USA: Digitalconference paper. p.241.

Chapman, D.R. and Frank, G. 2005. DesignConsiderations for Corrosion Protection in LargeDiameter Sewer Tunnel Construction. In: Proceedingsof the North American Society for TrenchlessTechnology - No-DIG 2005. Orlando, Florida, USA:Digital conference paper. Paper A-3-02.

Chapman, D.R. 2002. Selection and Design of CorrosionProtection Liner for Precast Concrete Segment TunnelLiner. In: Proceedings of the North AmericanTunneling Conference 2002. Seattle, Washington,USA: A.A. Balkema Publishers. p.171-182.

Kaneshiro, J.Y. ; Yankovich, D.R. and Kuhr, K. 2011.Gravity Sewer Tunnel Liner Corrosion Protection. In:Proceedings of the Rapid Excavation and TunnelingConference 2011. Englewood, Colorado, USA:Society for Mining, Metallurgy, and Exploration, Inc.(SME). p.589-612.

Wilshusen, T.P. ; Guardia, R.J. and Gil, J. 2012.Panama’s First Wastewater Tunnel. In: Proceedings ofthe North American Tunneling Conference 2012.Englewood, Colorado, USA: Society for Mining,Metallurgy, and Exploration, Inc. (SME). p.124-131.

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Recher, G. and Allain, S. 2013. Details onCombisegments® lining elements and investigation onreparation. Internal report. Telene SAS. Bondues,France.

Riechers, J. 2013. Sewer Corrosion Protection – One-passSegmental Lining Approach. In: Proceedings of the 1st

Arabian Tunnelling Conference 2013. Dubai, UnitedArab Emirates: Digital conference paper.

Telene® pDCPD chemical resistance – Non reinforcedgrades. www.telene.com. Telene SAS, 2014. Bondues,France.

The University of Memphis – Department of CivilEngineering in: CIVL 1101 – Properties of Concrete.Online course.

Herrenknecht AG, 2011. Panama Interceptor Project.Internal job-site report of tunneling process.Schwanau, Germany.

Japan Institute of Wastewater Engineering Technology,2002. Inner Surface lining Method for WastewaterShield Tunnels, Technical document.

one-pass segmental lining in a corrosive environment

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