1 INTRODUCTION 1.1 Importance of fixing technology in tunnel construction Tunnel structures belong to the most challenging civil engineering structures, thus require an increased degree of safety regarding planning, construction and operation in order to ensure greatest possible safety for people and environment, while at the same time cost budgets and time schedules must be met. Dense urban settings provide unique challenges for a number of reasons to tunnel construction. Building underground tunnels is not new. However, the way they are built today is very different to traditional mining techniques. Nowadays tunnel construction is totally mechanized, applying highly efficient and powerful technology and super performance construction materials. The excavation environment in a TBM bored tunnel is comparable to an industrial factory with high levels of safety and comfort for workers. Today it is possible to build tunnels much faster than some years ago. The operating life of tunnels is typically 100 years (Table 1). Tunnel projects categorized as strategically important engineering structure might be even planned for a service life of up to 200 years, as in case of the Brenner Base Tunnel running over 55km from Innsbruck/ Austria to Fortezza/ Italy.

Modern fastening systems in tunnel construction T.C. Czychy HALFEN GmbH, Germany A.S. Schulz HALFEN GmbH, Germany S.L. Lammert HALFEN International GmbH, Germany

ABSTRACT: State-of-the-art tunnels require extensive technical and operational equipment for safe and efficient operation. Depending on the type of tunnel, this may include electrification components, signal and lighting systems, communication equipment, ventilation and installation systems. The safe and sustainable installation of all equipment required is of vital importance. The paper gives some insights into the application of innovative cast-in channel fastening systems in representative tunnel projects. The positive impact on the planning process, construction efficiency or global cost as well as practical aspects such as installation and maintenance are explained in case studies of various global projects. Positive experiences in tunnels with precast concrete elements andin-situ structures have revealed the applicability of the cast-in channel system in different tunnel construction types. In particular the application in TBM built tunnels significantly contributes to higher site productivity associated with reduced labour, shortened construction time and lower cost. As labour costs, construction time, and safety issues have become more critical, cast-in channels are preferred alternatives to traditional methods such as post installed anchors. Adjustable and less dependent on the skill of the installer, they allow simple compensation for construction tolerances and fast, predictable installation programmes. In addition, recently increasing international concern regarding the use of chemical anchor bolts promotes the use of cast-in channels.

Underground Singapore 2016

Table 1. Indicative design working life (Eurocode 1990: 2002; Beton-Kalender 2014, Wilhelm Ernst & Sohn Verlag, Berlin, Germany)

–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Design working Ind ica t ive des ign Consequence Examples l i fe category working l i fe (years) Class 4 50 CC2 Bui ld ing st ructures and

Other common st ructures, s t ructura l tunne l equipment

–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 5 100 CC3 Tunnel , monumenta l , bui ld ings, br idges, dams –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 6 >100 to 200* CC4 St ra teg ica l l y impor tant in frast ructure key-

pro tect ive bui ld ings –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– * Life service Brenner Base Tunnel (BBT), Austria / Italy Due to the long operating life of tunnels it is important to define regular inspection- and maintenance intervals for the structure (Table 2). Table 2. Inspection- and maintenance intervals, Selection of building components in tunnels

(Beton-Kalender 2014, Wilhelm Ernst & Sohn Verlag, Berlin, Germany) –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Bui ld ing st ructure Inspect ion interva l l s Maintenance in terva ls Components ( years) ( years) –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Technologica l fac i l i t ies 1 1 Light ing 1 3 to 5 Sa fety systems da i l y 3 to 5 Tunnel vent i la t ion 1 5 to 10 Tunnel doors 1 5 to 10 –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– The high requirements in regards to the service life of the structure must be taken into consideration at best already in the preliminary planning and design phase. A multidisciplinary design approach, including geotechnical considerations, structural requirements, key tunnel elements such as ventilation, lighting, fire life safety, mechanical, electrical and control systems, material technology and lifecycle cost analysis, is required to realize a cost-efficient operation for the planned service life. The safe operation of tunnels greatly depends on the durable fixation of all required technical and operational equipment. The paramount superior objective to ensure safety of the installed equipment over the duration of the entire scheduled service life is not realizable without paying utmost attention to the correct design, selection and installation of suitable state-of-the-art fixing systems. For a safe and cost-efficient tunnel operation, the fixing technology used for the installation of the tunnel equipment is as important as the tunnel construction itself! While the initial costs of fixing technology are rather low compared to the overall tunnel cost, fixing failure could turn out at the end of the day highly costly and tragically for more than just the innocent victims! 1.2 Cases of fixing failure The following examples show possible consequences of fixing failure in tunnel construction.

1.2.1 “Big Dig tunnel collapse” in Boston/ 2006/ US: A massive suspended concrete panel fell from the tunnel ceiling and crushed a passing car, killing a 38-year-old woman and injuring her husband (Figure 1a). The proximate cause was the use of an epoxy anchor adhesive with poor creep resistance (Figure 1b), not capable of sustaining long-term loads. A total of about 26 tons of concrete and associated suspension hardware fell onto the vehicle and the roadway.

Figure 1(a) and 1(b). Photos from NTSB's report on Big Dig tunnel collapse 1.2.2 Sasogo tunnel accident/ 2012/ JP: On December 3rd, 2012, at the east-bound Sasogo Tunnel on the Chuo Expressway, precast concrete panels installed of ventilation ducts fell from ceiling. The total length of panel collapse was 130m. Fallen panels crashed 3 vehicles traveling in the tunnel (Figures 2). All together 9 persons were found dead and 2 injured. In the final investigation report chemical anchors were pointed out as an important root cause of this accident. During the following investigation it was found that only about 33% of the installed anchors could be verified with the required safety factor of over 3!

Figure 2(a) and 2(b). Sasago tunnel accident, collapse of the ceiling (Source: http://japandailypress.com/) 1.2.3 Swimming pool roof collapse Uster/ 1985/ CH: On 9th of May 1985 a serious accident happened in the internal swimming pool of Swiss city Uster. A suspended concrete-ceiling, weighing 200tons, collapsed and killed 12 people, 19 were injured. The ceiling was fixed with hangers made of stainless steel grade A2 (AISI 304). This type of stainless steel is very sensitive to chloride induced stress corrosion cracking – a fact unknown at that time. Today only approved anchors made of high resistant stainless steel (1.4529 or 1.4547) are officially allowed for these applications as they are considered to be safe in extremely corrosive environments for example in direct sea water contact, indoor swimming pools (chloride atmosphere) or road tunnels (traffic pollution – sulphur (IV) oxide).

2 FASTENING SYSTEMS 2.1 Overview There are two general types of anchor systems – cast-in place systems on the one hand and post-installed systems (drilled-in systems) on the other hand. While cast-in place systems are typically secured in the formwork prior to concrete casting, post-installed anchors are being installed subsequently in hardened concrete. An overview of the different types of both major anchor systems is given in the following illustration (Figure 3). Cast-in channels, also called anchor channels, are categorized as cast-in place anchor system.

Figure 3. Fastening methods in concrete Cast-in fixings such as anchor channels and headed fasteners as well as post-installed anchors are currently regulated in the European Technical Specification CEN/TS 1992 “Design of fastenings for use in concrete”. In future this specification will become part of the European Standard EC2/ EN1992. Before dealing with the selection and design criteria, the types of loads that anchors must withstand and load transfer mechanisms from the anchor into the concrete, are presented. Loads are mainly static or dynamic. Static loads can be tension, shear, or combinations of both. Dynamic loads can be seismic, wind, fatigue, or shock-like (e.g. impact forces). The different types of anchors available have properties that render them applicable or inapplicable for use under certain types of loads. The main anchorage mechanisms to transfer tension forces into the anchoring substrate are typically categorized as mechanical interlock, friction and bonding (Figure 4).

Figure 4. Fastener load-transfer mechanisms

Mechanical interlock is based on the interlock between fastener head and base material. Cast-in channels, headed anchors, undercut anchors or even certain types of threaded sleeves apply this mechanism. Friction is the transfer of load through friction between the expansion sleeve of the anchor and the borehole wall in the concrete. For chemical anchors employing the adhesive bonding principle, the resin adheres the fastener to the anchor base. The majority of nowadays available fixing systems resist tension loads via one of the above described principles or combine them. Before selecting a specific fastener it is an absolute requirement to understand its working principle. 2.2 Design considerations Various effects have to be taken into account during the selection of suitable fastening systems. Careful consideration is required in order to meet all technical and legal requirements. At the same time the selection must make good economic sense. Project delays and expensive overruns due to time-consuming rectification work by the contractor must be avoided as much as possible! In the following three important technical aspects on the choice of anchors will be described: Corrosion, anchoring base and installation. 2.2.1 Corrosion protection: A significant proportion of fixings is inappropriately specified from the corrosion point of view and cannot sustain for the intended service life. As a consequence costly rectification work is often required leading to troublesome interruptions in tunnel operation. Before any choice of fixing is made, corrosion possibly affecting an anchor must be carefully considered. Depending on the tunnel environmental condition the respective corrosivity category and risk can be determined (Table 3). Table 3. Atmospheric-corrosivity categories and examples of typical environments (EN ISO 12944-2, 5.1.2)

The determination of the corrosion category and risk of the specific tunnel environment in combination with the requirement for a defined service life and warranty requirements allows the engineer to select a suitable anchor surface finish or material. Since fasteners are typically classified as “non-replaceable” and “non-maintainable”, they must have a service life that corresponds to that of the particular system into which they are incorporated. In fixing engineering more and more stainless steel grades with excellent long-term corrosion resistance, even in challenging environments, are used. Although they seem to be more expensive, the extra costs are compensated relatively quickly by their longer service life and lower maintenance costs. 2.2.2 Anchoring base - concrete: The base material, usually concrete, and its quality is a decisive factor in the selection of the fastener. The influence of concrete crack width and compression strength of the typically reinforced concrete structures must be adequately considered in the anchorage design. Concrete crack width: Due to the low tensile strength of concrete, cracking due to external loading or thermal constraint is rather normal. If an anchor is positioned in a concrete tension zone, the concrete must be assumed by default as cracked. In accordance with international standards such as Eurocodes or British Standard, the acceptable crack width in reinforced concrete is limited to wk = 0.3mm under quasi-permanent load. Wider crack widths of up to wk = 1.5mm could occur if structures are subject to exceptional loading, e.g. earthquake, plane crash or explosions. Concrete cracking can play a decisive role in anchor design and performance. Cracks that occur near or even through the anchor location affect negatively the transfer of stresses into the surrounding concrete. The suitability of an anchor for the use in cracked concrete depends mainly on the type of load transfer mechanism (mechanical interlock, friction, bond). For the designer responsible it is important to select suitable fasteners, which are independently approved for use in cracked concrete! Certain bonded anchors are not suited for application in cracked concrete as the cracks eventually destroy the bond. On the contrary, headed anchors such as cast-in channels, based on the mechanical interlock principle, are generally suitable for the use in cracked concrete. The type of fastener to be used should be chosen with due consideration of the possibility of concrete cracking. Since cracks have a significant negative influence on the fastener performance, the engineering assumption that the anchor is situated in cracked concrete is reasonably conservative, especially when seismic behaviour is concerned. Compression strength: If the tunnel is being constructed using high concrete strength above 60N/mm², the suitability of the anchors must be carefully verified. It must be also considered that the actual concrete strength is often far higher than the nominal design strength. Concrete compression strength at around 80 to 100N/mm² can be found regularly. In particular torque-controlled and displacement-controlled expansion anchors are typically only approved for the use in concrete up to C50/60, hence they are not suitable if compressive strength is as high as mentioned above! Torque controlled anchors are not capable of creating the needed deformation in the concrete which is required for the bolt head to expand. Thus, the load would be held only by friction between the bolt and the smooth drilled hole. The resulting load capacity is typically unacceptably low. Displacement-controlled anchors cannot be successfully installed in such high strength concrete. For fixation into high strength concrete, anchors based on the mechanical interlock principle (cast-in channels, undercut anchors) are most suitable, as this type of fastener is not impaired by high concrete compressive strength or relies on the smoothness of the drilled hole.

2.2.3 Installation Whatever fastener system has been selected, the actual performance and usability of the individual anchor depends not only on the proper specification and accurate design but equally on the careful installation! For cast-in place systems it is crucial to install the fastener at the correct position and to secure it properly in position to avoid any shifting during concrete casting and vibrating. Once the concrete has hardened, the correct installation of a cast-in place anchors can be checked easily by visual means. Installation of post-installed anchors is much more complex and greatly depends on the skills of the installer and the installation equipment used. In the following section some installation relevant aspects are discussed. Drilling method: The drilling method has influence on the bond strength of anchor bolts based on adhesive bonding principle or displacement-control! In high-strength concrete drill holes are often diamond drilled, resulting in a smooth surface of the bore hole and low friction between anchor and concrete. Drill hole cleaning: In particular the performance of chemical anchors strongly depends on proper drill hole cleaning. Drill dust remainders in the hole reduce significantly the bond, resulting in an unknown load capacity! It is highly regrettable that in reality drill holes found on construction sites are very frequently not cleaned in a correct manner as can be seen in an exemplary statistics from a survey in Germany below (Figure 5). In other countries the situation is probably not better, more likely considerably worse.

Figure 5.Borehole cleaning on German construction sites, Survey 2007 (Eligehausen, 2014, Seminar in Melbourne: “Fastening to Concrete”) In order to accomplish the goal of correctly installed and properly functioning anchors, installation instructions should be detailed and clear, the installer should be well trained and must stringently follow the installation instructions of the manufacturer. The British Standard BS 8539 “Code of practice for the selection and installation of post-installed anchors in concrete and masonry” provides recommendations for the safe selection and installation of anchors. The intention is to provide practical guidance for designers, engineers, manufacturers, suppliers, contractors, installers and testers of anchors. BS 8539 is also linked to the relevant European regulations, especially with respect to the selection of products with the correct ETA’s for the application.

3 CAST-IN CHANNELS 3.1 Introduction A cast-in channel consist of a cold- or hot-rolled C-shaped steel profile and at least two anchors, non-detachably fixed on the profile back (Figure 6a). Cast-in channels belong to the cast-in place fastener systems and are installed prior to concrete casting. They are fixed onto the formwork. After curing of the concrete and striking the formwork, the foam filling inside channel is removed and the channel is ready for the installation of fixtures. T-headed bolts with accompanying nuts and washers are supplied for fixing any structural elements.

Figure 6(a) and 6(b). Hot-rolled cast-in channel with T-bolt; Full adjustability in channel length direction Due to the design, standard channels can carry loads in direction tension and transverse shear direction (Figure 7a). To carry also loads in the longitudinal direction, a new generation of cast-in channels – type DYNAGRIP - was developed. These hot-rolled channels, equipped with serrated channel lips are equally strong in all directions (Figure 7b). Hot-rolled, serrated cast-in channels have been also successfully tested for the application under fatigue, seismic or impact forces.

Figure 7(a) and 7(b). Load bearing directions of standard (non-serrated) and serrated anchor channels 3.2 Advantages of cast-in channels Cast-in channels allow an adjustable (Figure 6b), safe and efficient installation of fixtures, especially if they are used in prefabricated concrete elements. The installation of channels in the precast factory guarantees highest precision and steady quality. Precast concrete members can be delivered to the construction site, an integrated fastening system included. This is saving construction and installation time significantly compared to conventional post-drilled anchor systems. Drilling operation on site can be completely eliminated and with that all the risks involved with drilling operation, such as damages to reinforcement or concrete and installation time required.

The fixing position can be easily adjusted along the channel slot, thereby compensating unavoidable construction tolerances. Channels provide also flexibility in changing the fixing position or replacing the fixtures during the life cycle of structures. Since the time consuming and fault-prone drilling and welding operations can be completely eliminated, the use of cast-in channels stands for a significant increase of site productivity with reduced labour and increased safety. 4. CASE STUDIES Cast-in channels have been successfully employed as preferred fastening systems in numerous tunnel projects of different construction type across the globe. The positive impact on the planning process, cost and planning security, the increased construction efficiency as well as the significant improvement on quality and safety aspects are being explained by the following case studies. Because the application of cast-in channels in on-site concrete construction tunnel projects is well established since decades, in the following case studies special emphasis is put on bored tunnels with precast concrete segmental lining, a construction technique often selected in dense urban areas in order to minimize associated environmental impacts or local traffic disturbance. 4.1 High speed railway tunnels (HSR tunnels)/ Germany 4.1.1 The Finnetunnel The Finnetunnel (Table 4) is an essential part of the new German railway line between Erfurt and Halle/ Leipzig on the Verona – Munich – Berlin axis and will allow speed of trains up to 300km/h. The tunnel tubes were created by means of tunnel-boring machines and subsequently lined with precast tunnel segments. The production of around 48.000 pcs of Tubbing-Segments started in the early 2008 at a mobile precast-factory on site. The ring design consists of 6 complete sections and a key stone half the size of the other sections, the segments are designed with a left- and right conicity. Each ring section measures 2 m in width and 450mm in thickness. Table 4. Project data - Finnetunnel –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Tunnel length 2 x 6 .970 m (2 para l le l s ingle t rack tubes) Tunnel d iameter 9 ,6 m Construc t ion t ime 04/2008 – 12/2011 Anchor channel type Hot-ro l led HTA52/34, A4 (AISI 316) , curved Ri = 4800 mm Tota l length o f channels 8 .000 m –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– A vital part of the technical equipment for the tunnel is the overhead line system. To meet the demands of high-speed traffic, the continuous main rails were transferred with an overhead line of the control type Re330. This type, specifically designed for high-speed traffic, consists of modules made up as much as possible of standardized elements and components to ensure high efficiency and cost-effectiveness when it comes to maintenance and repairs of systems. For mounting the Re330 overhead lines cast-in channels, embedded in the precast concrete tunnel segments, have been used (Figures 8). More than 4.000 m of anchor channel-pairs were precisely installed in the precast factory, exactly following as the detailed construction documentations specified. To ensure that practically no maintenance is needed during the entire service life, the channels were specified in stainless steel grade A4 (AISI 316), following the standard technical specification by German Rail DB. The channels are short-circuit proofed since they have been connected via special connectors onto the reinforcement installed in the segments and are incorporated into the tunnel earthing system. Decisive factors for German Rail DB as operator to specify the cast-in channels as default fixing system, are the high degree of adjustability during the installation and life cycle, the prevention of defects caused by drilling dust, reduction of interfaces between different contract work sections and consequently reduction of warranty interfaces, the robustness and durability.

Figures 8(a) and 8(b). Precast segment with installed pair of cast-in channels; after overhead system installation 4.1.2 The Boßler Tunnel The Boßler Tunnel is currently under construction in the section 2.2 “Albaufstieg” on the new high speed railway line Wendlingen – Ulm by German DB as part of the upgrading of the central European West-East rail corridor. Bored with TBM, the lining of the tunnel consists of heavy-duty precast concrete segments. For mounting the overhead line system hot-rolled cast-in channels are being used. For the fixation of the channels onto the steel formwork an innovative fixing system, employing special steel fixing cones and plastic fixing screws with break-off point, has been successfully used for the first time (Figure 9a). For lifting and setting of the tunnel segments vacuum erectors are used (Figure 9b). To ensure the seal-tightness between erector and concrete, special tape is placed over the cast-in channels before lifting, a technology developed in cooperation between the erector supplier, precast factory and HALFEN.

Figures 9(a)and 9(b). HALFEN fixing cone system; lifting the precast segment with the vacuum erector

4.2 Subway tunnels – Shenzhen Metro line 9/ China Shenzhen line 9 was the first Chinese metro line that employed a state-of-the-art cast-in channel system as fastening system for all technical and operational equipment such as overhead conductor rail, M&E equipment or escape route cat walks. Hot-rolled, serrated cast-in channels, applicable for 3-D loading and resistant to seismic impact, were installed in all tunnel segments to provide almost continuously fixing lines across the tunnel cross section (Figure 10).

Figure 10. Segmental lining layout with hot-rolled, serrated cast-in channels, type DYNAGRIP HZA 29/20 4.3 Utility Tunnel – BEWAG Berlin / Germany As from 1995, a 3m-diameter HV-cable tunnel was built in order to link the western part of Berlin´s power supply to the 380 KV network (Table 5). The tunnel consists of a 8.5 TBM drilled tunnel section and a 2,9km precast pipe section. In both sections the 6 heavy 380 KV-VPE plastic cables, each with a diameter of 15cm, are set on supports, which are mounted on HALFEN cast-in channels (Figure 11a). Additionally the channels were used for supporting the suspension rail system, used by staff to inspect the tunnel (Figure 11b) and tunnel lighting. Table 5. Project data - BEWAG Utility tunnel –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Tunnel length 11.400 m Tunnel d iameter 3 .0 m Construc t ion t ime 1995 – 1999 Anchor channel type Hot-ro l led HTA52/34, HDG, curved Ri = 1500 mm –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– The technical specification of the construction of the tunnel did not allow for post-drilling into the concrete segments in order to eliminate any risk of serious damages to the concrete or the reinforcement installed. Further important considerations for the selection of the most suitable fastening systems were cost-efficiency, high construction speed and short tunnel fit-out phase, fire resistance, robustness and durability as well as flexibility for potential future layout modifications or replacements. After a thorough analysis of the technical feasibility and economy it was eventually decided to apply the HALFEN cast-in channel system.

Figure 11(a) and 11(b). Cable support consoles fixed onto embedded HALFEN rails; maintenance vehicle

5. CONLCUSION Concrete fasteners are used in tunnel construction and play a vital role to enable reliable operation. The safety and reliability of anchorages largely depend on three aspects: selection of suitable anchors, proper design and correct installation. In general planners and operators can choose between post-drilled anchors or cast-in place systems. In particular cast-in channels have been established over the last years as preferred alternatives to traditionally used drilled anchor solutions. In comparison to post-installed anchors they are much less sensitive to the challenging boundary conditions on site. As fixtures can be enormously fast and adjustably mounted onto the cast-in channels during the initial tunnel fit-out phase and likewise throughout the entire operational phase, this forward-thinking fastening concept offers the highest degree of construction efficiency, allowing trouble-free modifications and refurbishments in future. When used in precast tunnel segments, cast-in channels increase significantly quality and safety, as the channels will be already installed and inspected in a controlled environment of a precast factory. This results in high precision and steady quality. Precast tunnel segments with integrated cast-in channel fastening systems allow the immediate use on site without any further drilling works or expensive quality checking effort. A substantial reduction of construction and installation time in connection with an increase of site productivity with reduced manpower on site can be achieved. Last but not least the installation of fixing anchors in the precast factory reduces interfaces between different contract work section and consequently the reduction of warranty interfaces. 6. REFERENCES BCA, Building Construction Authority. 2014. BS 8539 – Standard on the use of post-installed anchors for structures requiring plan approval. Circular CFA, Construction Fixings Association. 1995. CFA Guidance note: Fixings and Corrosion CFA, Construction Fixings Association. 1995. CFA Guidance note: Resin Bonded Anchors CFA, Construction Fixings Association. 2014. How to install anchors in accordance with BS 8539:2012. A guide for contractors & installers Eligehausen, R. Malee, R. & Silva, J.F.2006. Anchorage in Concrete Construction. Ernst & Sohn Verlag, Berlin Eligehausen, R. 2015, Safety concept of anchorage according to EN 1992-4. Seminar “Anchor Bolts for Nuclear Power Plants – Applications, Design and Assessment”. Stockholm EOTA, European Organisation for Technical Approvals. 2013. European Technical Approval ETA-09/0339 for HALFEN anchor channel HTA DIBt Deutsches Institut für Bautechnik 2015. Approval Z-21.4.-1691 Approval for Halfen anchor channel HZA 29/20, HZA 38/23, HZA 53/34 and HZA 64/44 Güres, S. 2005. Loadbearing Behaviour of Anchor Channel Fastenings under Non-Static Loads. Doctor Thesis. University of Bochum/ Germany Kraus, J. 2003. Loadbearing Behaviour of Anchor Channels under Centric Tensile Loading. Doctor Thesis. University of Stuttgart/ Germany Schmid, K. 2010 Behavior and design of fastening at the edge with anchor reinforcement under shear loads toards the edge. Doctor Thesis. University of Stuttgart/ Germany Seibold, G. 2003. Demands on Plugs and Anchors in Tunnels. Tunnel technical journal Smeets, W. 1993 Anchor Channels for adjustable Fastening on Conrete Constructions. Study Group for Prefabrication – Facade and Transportation Anchorage, Pages 23-41, Wiesbaden