PORR ProjectsWorld of PORR 169/2016

Stefan Plankensteiner, Thomas Steinwender

IntroductionThe B180 Reschen Straße is a country road in Tyrol that runsfrom the end of the motorway feeder road in Fließ through theUpper Inn Valley to the border with Italy shortly beforeReschen Pass, which also gives it its name. Built in 46 afterChrist, the Roman Road named Via Claudia Augusta was thefirst navigable road crossing Reschen Pass. All through theMiddle Ages and all the way up to early modern times, itranked among the most important historic alpine crossings.Between 1850 and 1856, a new road, starting at Kajetansbridge in Pfunds was built in extremely steep rocky terrain.The road ascends some 400 metres to Nauders viaHochfinstermünz and the Finstermünz Pass. Located inHochfinstermünz, Nauders Castle is an outer fort erected in1840 and today houses a military museum. Reschen Straßeranks among the most important north-south connections inthe Alps. Therefore, some 2,600m of protective structureswere built along this high-alpine route section in the past 30years to protect the population, tourism and through-trafficfrom natural hazards. Avalanches and rockfall are commonoccurrences in the area of Hochfinstermünz. This is why theProvince of Tyrol, in its role as client, has decided to build amore than 275m long avalanche and rockfall gallery in thislast undeveloped and rockfall-endangered section of theB180. Thus, drivers using this road which is frequented by upto 4,500 vehicles per day can get to Nauders or further on tothe Southern Vinschgau region (South Tyrol) in even moresafety.

Existing structure – natural tunnel at milestone 60Image: PORR AG

Hochfinstermünz – Nauders Castle / at the beginning of the contract sectionImage: PORR AG

OrderIn May 2014, the Office of the Tyrolean Government’s Trafficand Road Section, Bridge and Tunnel Construction,commissioned TEERAG-ASDAG’s Tyrol branch (now: PORRBau GmbH, Tiefbau), with the construction of the 320-mgallery incl. expansion of the natural tunnel. The contract’sitem was the new construction of the structure known asNiklasgalerie on the B 180 Reschen Straße from km 30.22 tokm 30.66 in the municipal area of Nauders. Apart from theconstruction of the avalanche and rockfall gallery and theassociated road construction work, an approx. 45-m-longnatural tunnel was to be expanded, the Stillerbach bridge atthe contract section’s beginning was to be widened and toreceive a new superstructure and several retaining walls wereto be installed. Furthermore, a catch basin and seepagechannels were to be built, the Stillerbach bridge’s existingfoundations were to be underpinned and the dam on the leftshore of the Labaunerbach brook was to be extendeddownstream in an arched shape to the estuary of theStillerbach brook. To secure the gallery’s foundations on thevalley side, the slope on the left shore as well as theStillerbach brook’s bed were to be equipped with riprap andthe like.

ProjectFrom portal to portal, Niklasgalerie is some 320m long andwas built in 18 sections with standard lengths of 15m each.The gallery was built with a flat ceiling. The superstructure’sthickness varies and amounts to at least 90cm. An existingnatural tunnel some 45m in length in the road axis divides thegallery into a northern part 226.5m in length and a southernpart 48.5m in length. The structure’s rear wall was executedas a reinforced concrete angled wall and monolithicallyconnected to the gallery’s ceiling. The gallery’s supports onthe valley side were founded on strip foundations, as werethe walls on the mountain side. The foundations on the valley

B180 Reschen Straße – New construction ofNiklasgalerieAvalanche gallery in high alpine terrain

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PORR ProjectsWorld of PORR 169/2016

side were equipped with a cover and the accruing loads weretransferred into the ground by means of micro piles.

Located at the beginning of the contract section, theStillerbach bridge’s superstructure through the gallerystructure was executed as a truss structure some 30m inlength on the upstream side. Connecting to the natural tunnelon both sides are gallery blocks angular in terms of theirground plan. At 0.9m x 0.55m, the supports’ dimensions areequal along the entire length of the gallery. The supports’height thereby varies depending on terrain and foundationtype. The supports of blocks 1 and 2 rest on an edge girdernext to the Stillerbach bridge’s superstructure. The supportsof blocks 3 to 5 rest on a retaining wall to be built in this area.All other blocks’ gallery supports are founded on regularfoundations which means block foundations with micro piles.Niklasgalerie serves to compensate rockfall loads and wastherefore built with a massive covering (1.20m – 3.8m). Thesuperstructure features dual-layer bituminous sealing whichwas equipped with sealing protection.

Preparatory work began in July 2014. A 400-m dual-trackconstruction site bypass with a temporary bridge crossing theStillerbach brook and a corrugated passage at theLabaunerbach brook had to be built to allow this constructionscheme to be implemented. In the course of this procedure,three historic tanks from WWII as well as several cannonswhich had been on exhibit in the area of the future bypassroad had to be loaded onto flatbed lorries and transported toPontlatz Barracks in Landeck in spectacular fashion.

Loading of historic tanksImage: PORR AG

Main construction work (gallery and road construction)including opening to traffic was complete in 2015. Remainingtasks were to be completed and recultivation work was to beimplemented by June 2016.

Removal, excavation and rock stabilisation workIn terms of technology and construction logistics, theconstruction scheme presented a tough challenge for thepeople in the employ of TEERAG-ASDAG and PORR'sFoundation Engineering Department. In a first step, the rockfaces on both sides of the valley needed to be cleared andpermanent rockfall protection fences

in portal areas and temporary rock fall protection fences in theremaining area of the contract section had to be installed toguarantee the workers’ safety. Furthermore, comprehensiverock removal and slope stabilisation measures (shotcrete soilnail wall) needed to be carried out in the run-up to allow forthe project’s implementation.

Natural tunnel expansionThe existing, some 45-m-long natural tunnel needed to beexpanded to achieve the new gauge. Both blasting drivingand mechanical methods were used to expand the tunnel,always guaranteeing a minimum of strata degradation. Tosecure the “rock column” on the valley side, it was supportedby means of untensioned anchors. Cracking support for thetunnel was provided by a 15-cm-thick shotcrete shell with areinforcement layer on the mountain side and steel gratingarches as well as system anchoring using SN anchors. Thiswork was likewise completed in November 2014.

Natural tunnel – expanded and securedImage: PORR AG

Stillerbach bridgeBuilt in the time of the Austrian-Hungarian Empire, theStillerbach bridge consisted of a 5-web tee-beam. In thecourse of route regulation in 1954, this old superstructure wasreconstructed and widened by means of superstructureelements triangular in shape. Measured obliquely, the spanamounts to some 21 metres. The two edge girders are 1.75mtall. The new bridge superstructure was executed as anangled reinforced concrete slab with edge girders along thebridge’s free edges and reinforced girders in the bearingaxes. The crossing angle with the brook axis is 45°. Thebridge’s vertical span is 7.6m. Due to the bridge’s gradient,the span of the edge girders is 22.2m and the length of theedge girders 25.7m each. To support the wider bridgesuperstructure, the existing abutment walls upstream neededto be extended by some 6.10m (right) and 7.2m (left). Theuppermost parts of the existing abutment walls were removeddown to a depth of some 2.2m below the road surface tomake room for the new abutment structures. The abutmentswere founded on approx. 20-m-long micro piles with adiameter of 63.5mm and a yield stress of 1,742kN. Due to thereinforcement girders in the bearing axes located underneaththe superstructure slab and the edge girders along the freeedges, the extremely slanting superstructure slab

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PORR ProjectsWorld of PORR 169/2016

(thickness: 0.45m) was enclosed at all four edges. The slabborders the edge girders which are 1.28m tall in total. Thereinforcement girders in the bearing axes reach some 1m intothe superstructure’s bottom edge. A slanted superstructurelength of 26.2m in total and the superstructure’s width of12.9m results in a bridge deck area of some 338m². Thesuperstructure was covered and the open land road surfacewas executed in full thickness. An additional girder entirelydisconnected from the bridge superstructure was installed forthe gallery supports located upstream. A truss needed to bebuilt to accommodate the enormous vertical loads of thegallery roof. The additional girder next to the bridge formedthe truss construction’s lower wing. The gallery roof’ssuperstructure slab serves as the truss’s upper wing. Fourcolumns as well as the diagonal struts placed between thefirst and second as well as between the third and fourthcolumn yield a massive truss construction. On the bridge, thegallery structure could only be built by supporting it using thebridge superstructure which was itself still supported.

Concrete construction for the gallery’s structural frameAfter the scheduled winter break 2014/2015, mainconstruction began in March 2015. The gallery structure wasexecuted as a structural frame construction with supports onthe valley side. In the first construction stage, the northerngallery section (blocks 1 – 15) with a length of 226.5m wasconstructed adjacent to the overbuilt Stillerbach bridge. Whilethe foundations on the mountain side were installed (width:4.5m), the team began building the foundations for the valleyside supports (width: 3m). The foundations on the mountainand valley sides were executed as strip foundations. Thefoundations on the valley side were built using S 555/700GEWI micro piles with a diameter of 63.5mm and ribbedthreads as well as dual corrosion protection. In the rock, thebond length was 8m, in the loose material some 20m. Thiswas followed by the installation of the 80-cm-thick, slightlyhaunched wall slab more than 5m in height on the mountainside. On the valley side, the supports with a cross section of55 x 90cm were built simultaneously. In June 2015, the teamon site began assembling the gallery form work carriage.Following the form work carriage’s assembly, the first of 18superstructure blocks with a regular length of 15m wasconcreted in early July.

Construction of blocks 1 and 2 / Stillerbach bridge superstructureImage: PORR AG

Gallery construction, northern section 2015Image: PORR AG

Gallery formwork carriageImage: PORR AG

3D view of block 10Image: PORR AG

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PORR ProjectsWorld of PORR 169/2016

Aerial shot: gallery construction 2015Image: PORR AG

Furthermore, building the transition blocks 15 and 16connecting to the natural tunnel in an arched shapepresented the team with a tough technical challenge.Comprehensive adjustment work regarding formwork neededto be implemented in this context. With the southern gallerysection (blocks 16 – 18) at a length of 48.5m, mainconstruction work was completed in November 2015.

A natural tunnel divides the two gallery sections.Image: PORR AG

Gallery construction, southern section 2015Image: PORR AG

While the gallery structure was constructed, the plasterrecesses on the mountain side and the drainage lines for thedrainage of water coming down the slope were installed. Thegallery’s sealing was also drawn in. A 47-m retaining wall onthe mountain side was installed after the gallery structure inthe direction of Nauders had been completed.

Completion of natural tunnelThe 45-m-long natural tunnel was lined at the same time asthe gallery’s construction advanced in November 2015. Aftera sealing carrier and a drainage mat had been applied, thetunnel was equipped with a plastic sealing sheet (umbrellasealing). Due to the tunnel’s moderate length, the inner liningwas executed as a 20-cm-thick dual-layer shotcrete innerlining. A protective layer was applied to the plastic sealingdue to the reinforcement. The inner lining’s reinforcementmats were attached to grid arches and anchors executed aswaterproof penetrations of the plastic sealing.

Inner lining – shotcrete shell natural tunnelImage: PORR AG

Back filling / road constructionFollowing the completion of concrete and sealing work, backfilling the gallery started in October 2015. For this purpose, atemporary ramp allowing access to the gallery roof had to bebuilt close to the natural tunnel. The dual layer sealing wassupported by means of a drainage mat after which a 50-cm-thick protective layer with a maximum grain size of 80mm wasapplied to the superstructure slab. Due to the immediatelyadjacent rock in most areas, back filling was performed usingfilter gravel in certain places. In areas that allowedcompacting, back filling was installed and compacted layer bylayer. After the completion of drainage and road constructionwork in December 2015, the new gallery could be opened totraffic for the first time just in time before the winter season of2015/2016.

After the winter break, remaining tasks were completed in thespring of 2016. These included, among others, the completionof the edge girder at the gallery roof, the installation of thegabions which, with their alpine appearance, harmoniouslyblend in with the landscape and allow for amplecompensation of rockfall loads through an up to 3.8-m-thickbackfill on the gallery roof. The temporary access road wassubsequently removed, hydraulic engineering work on theStillerbach brook completed and the entire contract sectionrecultivated. Finally and without restrictions, the constructionscheme was opened to traffic in June 2016.

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PORR ProjectsWorld of PORR 169/2016

Incorporation of Stillerbach bridge into NiklasgalerieImage: PORR AG

Nauders gallery portalImage: PORR AG

Hochfinstermünz gallery portalImage: PORR AG

Road – driving space in gallery structureImage: PORR AG

Connection of gallery structure with natural tunnelImage: PORR AG

Final remarkThanks to excellent collaborations between all projectparticipants – from the client to local building supervision andauthorities – work proceeded to the great satisfaction of allthose involved and the section could be completed andopened to traffic in June 2016. The biggest challengesTEERAG-ASDAG AG and all those involved in the project hadto face were keeping traffic moving in the construction sitearea on the one hand, unsteady weather conditions insummer and winter, local framework conditions (spatialrestrictions) and the construction site’s topographicallydifficult location in Alpine terrain on the other. With thisproject, PORR, in cooperation with several corporatecompanies, once again proved its experience and expertise inthe areas of infra-structure and road construction, just as ithad done in the course of the other large Tyrolean galleryprojects it had processed in recent years.

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PORR ProjectsWorld of PORR 169/2016

Project data

Client The Office of the Tyrolean Government,Bridge and Tunnel Construction

Contractor TEERAG-ASDAG AG / Tyrol branch(today: PORR Bau GmbH, Tiefbau)

Contract volume EUR 6.9m

Start ofconstruction

July 2014

Final completion June 2016

Project length 440m

Road surface 4,300m²

Excavatedmaterial, earthmoved

17,000m³

Frost layer 3,000m²

Ready-mix 2,000t

Tunnel/gallerystructures

320m

Concrete volume 9,300m³

Reinforcing steel 1,400t

Shotcretesurface

720m²

IBO anchors 750m

Micro piles 7,300m

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