Smart solution for rescue tunnels
Two new rescue tunnels are set to improve safety in one of Germany's oldest road tunnels. The tunnels will reduce the length of the escape routes from the 622 m long Lämmerbuckel Tunnel while bringing its safety provision into line with contemporary standards.
Data & Facts
Rescue tunnels in Lämmerbuckel Tunnel, Wiesensteig (GER)
Division IU Tunnelling,
Ed. Züblin AG
Engineering and support
MEVA Schalungs-Systeme GmbH, Haiterbach, Germany
Innovative design needed for Lämmerbuckel Tunnel modernisation
"Given the importance of Germany's A8 motorway as an east-west corridor in the national network and its high traffic volumes, proper tunnel safety can save lives in emergencies," explained Wolfgang Reimer, President of Stuttgart Regional Council, at the ground-breaking ceremony for the tunnels. On the modestly sized, though still highly demanding construction project, MEVA assisted contractor Ed. Züblin AG with the detailed planning, providing both creative standard solutions and specially designed formwork.
In terms of construction, the only significant difference between the two rescue tunnels is their length. This allowed use of the same formwork for both. The first step was to construct the end walls connecting the rescue tunnels to the existing road tunnel. To form the junction with the arch of the new mined tunnel section, specially designed formwork was required for the top part of this connecting wall. The single-sided formwork, comprising Mammut 350 wall formwork and special components, was held in place by the STB 300 support frame, which is suitable for pour heights up to 3.30 m. Detailing of the special formwork also provided for incorporation of the required internal waterstops.
Rucksack packed and ready to goThe first section of the rescue tunnel directly adjoining the end wall contains a niche for the electrical installations, where the standard tunnel profile widens out. The solution adopted by the contractor to meet the exact dimensional requirements involved the use of so-called "rucksack" formwork, precision-fabricated by MEVA's engineers. To ensure precise mounting of the special semi-circular unit on the formwork carriage and in the tunnel niche, the rucksack formwork was first positioned in the reinforcement. The formwork carriage was brought into place and accurately aligned below it. The pre-fitted connectors were then tightened in order to firmly secure the special assembly to the carriage. Rubber sections attached to the formwork provided the necessary waterproof barrier between rucksack formwork and carriage.
At their ends, the mined sections of each rescue tunnel join onto a further cut-and-cover section. To form the junction between the two different profiles, MEVA’s formwork engineers designed special timber units. These served as a means of securing the waterstops in the transitional section and as formwork for the junction between the round and rectangular tunnel profiles. Here, the special timber forms were applied as a facing to the Mammut 350 wall formwork and were later reused as stop-end formwork in the cut-and-cover tunnel section. Mammut 350 was then used for all remaining operations. With a fresh concrete load capacity of 100 kN/m², the product is ideal for civil engineering applications while also offering a wide range of panel sizes from 1.25 m x 0.25 m to 3.50 m x 2.50 m.
Project wings its way to completion
The tunnel inverts were formed using horizontally placed wall formwork units. With no vertical extensions needed to build the 3 m high walls thanks to the large Mammut 350 panel sizes, the rest of the works proceeded apace. The formwork was positioned and supported by EuMax props fixed diagonally to the excavated pit slope. Their flexible extension length and large range for fine adjustment allowed trouble-free setting. Accordingly, the walls for the outer sections of the two tunnels were completed in three and four cycles respectively. Mobile MEP slab tables with MevaFlex were then used to cast the ceiling slabs. The two rescue tunnels terminate in diagonal wing walls with canopy. These primarily serve to retain the ground and create a level entrance to the tunnels.
Clearly targeted formwork design
Site manager Alfred Elst was very satisfied with the completed works and had a special word of praise for the carefully targeted, practice-oriented formwork design. “The rucksack formwork developed by MEVA was a perfect fit and the 3D drawings were also very useful,” he explains. “They show the details very clearly and simplify formwork assembly.”