The new ICE high-speed line between Wendlingen and Ulm, just on 60 km in total length, is currently under construction in the south-east of the Stuttgart metropolitan region as part of the expansion of the pan-European high-speed rail network. A good half of this line, 30.4 km in all, will run underground, in ten tunnel structures. The 8.8 km long Boßler Tunnel located on the Albaufstieg ascent, for example, and also the directly connecting, almost 4.9 km long Steinbühl Tunnel, have already been under construction here for a number of years.
A further major project – the around 8.3 km long Albvorland Tunnel, near Kirchheim unter Teck – has now been started, and is the final tunnel-construction project, closing the remaining gap between Stuttgart and the Swabian Alb. The alignment of this tunnel, also to be headed using mechanised shield tunnelling, will pass under a high-pressure gas pipeline, a NATO fuel pipeline and, for a distance of around 1.3 km, also the Stuttgart-to-Munich Autobahn 8. Maximum safety is also needed for this project, with overburdend varying from a maximum of 65 m to a minimum of only just on 9.50 m and head of water of up to 45 m.
Maximum Safety for Segment Sealing
This enhanced safety awareness was also reflected in the technical schedule of works for the segment seal in the context of the project tendering stage. The project client, Deutsche Bahn Netz AG, had applied in advance a safety allowance to the design water pressure for planning of 4.0 bar and raised this figure to 5.0 bar, resulting in a test pressure of 10 bar in accordance with the Ril 853/ZTV-Ing. specifications and contractual conditions for the qualification certificate to be furnished for the segment seals. This was to be demonstrated taking account of the initial design joint gap and an additional gap expansion of 6 mm and strictly in accordance with the provisions of the TL/TP DP (Technical Conditions of Supply and Technical Inspection Regulations for Sealing Profiles) code of practice, i.e., with misalignment („offset“) heights of 0 to 20 mm. The contractor entrusted with construction of the tunnel, Implenia Construction GmbH, in fact enforced still further safety margins for the specifications stipulated by DB Netz AG for the tightness test certificate by demanding from the manufacturer of the elastomer sealing gaskets additional tests for a simulated „worst case“ involving an 8 mm joint expansion and a 20 mm misalignment.
Development of a new Sealing Profile Geometry for the Albvorland Tunnel
DB Netz AG specified a minimum contact width of 38 mm for the sealing-profile geometry to be used, which closely approximated to a „classical“ sealing strip for a groove-base width of 44 mm as previously used in various rail-tunnel projects.
It had to be assumed, on the basis of test results obtained in conjunction with previously completed rail-tunnel projects using various 44 mm sealing strips, that a critical boundary zone would be involved even alone with the test parameters specified by DB Netz AG, i.e., a joint expansion of only 6 mm.
This induced CTS Cordes Tubes & Seals GmbH & Co. KG to enter into the development of a new suitable sealing profile geometry specifically for the test requirements applying for the Albvorland Tunnel (Fig. 1). Cordes, based in the Münsterland region of Westphalia, has developed and manufactured elastomeric sealing systems for concrete pipes and manholes for more than fifty years and has also been known for around fifteen years as a producer of special sealing systems for use in pipe jacking and for launch-shaft structures. CTS Cordes Tubes & Seals, a member of the Cordes group, has also developed and manufactured sealing systems for waterproofing of segmental lined bores since 2016. Special starting seals produced by CTS Cordes with an individual weight of around 750 kg in each case, which assure smooth transition of the tunnel-boring machines out of the launch shaft, are also in use on the „Albvorland Tunnel“ project.
In addition to a significant improvement in sealing performance across all misalignment heights, attention also had, at the same time, to be devoted in the development of a new profile for the segment seal to the requirement expressed by the client for „moderate“ restoring forces. In this context, Implenia Construction GmbH had already given advance thought to this during the evolution of the segment design, and provided a special groove design to accommodate the segment seal. A resulting limitation of the minimum possible groove-base spacing to 26 mm to reduce the degree of compression of the sealing profile and a raised lip close to the sealing groove – necessary to assure sealing performance– was considered advantageous by CTS Cordes. The development of the new profile geometry and all laboratory tests performed in conjunction with this were thus explicitly tailored to this design parameter and the sealing groove and segment joint design (Fig. 2).
After intensive Research & Development work and product tests performed mainly at the MPA in Hannover, which were conducted across a period of several months, a totally new profile geometry was achieved.
The advantages of this newly developed geometric concept can be found, essentially, in the form of a considerably greater sealing effect, which exhibits no significant, geometrically induced fluctuations whatsoever across all joint-misalignment dimensions. It was thus possible to demonstrate fulfilment of the minimum tightness requirements for „joint expansion = 6 mm“ in accordance with the project specification across all misalignment heights and with significant additional reserves.
The resultant overall concept for groove design and profile optimisation permitted the above-described improvement in sealing action with no significant increase in the maximum restoring forces with the smallest joint gap. It was possible to achieve a test pressure of 10 bar even in the „worst case“ tests performed additionally with a joint expansion of 8 mm (i.e., a groove-base spacing of 34 mm) and a misalignment of 20 mm.
The extensive tightness tests performed at the MPA in Hannover were then augmented by additional product tests. The test proofs for force/stroke behaviour on the sealing profile and also for long-term relaxation behaviour in a simulated installation test, both also required in accordance with the TL/TP DP, were thus also conducted at the MPA in Hannover (Fig. 3).
CTS Cordes also performed a simulation test for verification of the plot of restoring forces in the critical T-joint (Fig. 4). This proof was furnished using the gasket corner design with reduced injection-moulded lengths for reduction of restoring forces specially implemented by CTS Cordes.
The concept forming the basis for this geometrical structure has now also been applied to smaller profile dimensions, such as the CTS 36/18 and CTS 33/16 gaskets for the classical groove-base widths of 36 mm and 33 mm. CTS Cordes perceives in this new profile generation a technological advance, particularly in the case of projects with particularly high tightness requirements.
The exceptionally great scope of certified performance tests conducted for various functional properties of the tubbing seal, a major portion of which were performed at the independent materials-testing institute for the construction industry in Hannover, entirely in accordance with the requirements of the Ril 853/ZTV-Ing. specifications and contractual conditions, provided an initial basis for approval of the new CTS 44/20 „AVT“ sealing profile concept for the Albvorland Tunnel. In addition, a specific testing schedule for in-production quality and periodic tests in gasket production at CTS Cordes was also drafted in close cooperation with the client.
Production of nearly 55 000 Gaskets by the End of 2018
Under these preconditions, the client, Deutsche Bahn Netz AG, granted approval for the new „CTS 44/20 Albvorland Tunnel“ sealing profile, and deliveries thus began in June 2017 (Fig. 5).
Series production has been ongoing at Implenia Construction GmbH‘s tubbing plant at Kirchheim unter Teck since as long ago as July 2017, in order to assure the availability in good time of an adequate stock of prefabricated segments at the TBM start-of-operations date in October 2017 (Fig. 6). CTS Cordes Tubes & Seals GmbH & Co. KG aims to make its contribution to the completion of this demanding tunnel project by supplying a total of 54 740 precisely fitting gaskets on schedule by (forecast) December 2018.
Andreas Diener, CTS Cordes tubes & seals GmbH & Co. KG,Senden, Deutschland/Germany