Automated cost optimization of the inner lining of the second Lötschberg base tunnel tube

To be able to realize the integrated synchronized timetables in long-distance traffic and to increase the capacity in freight traffic between Brig and Bern, the two-lane extension of the Lötschberg Base Tunnel (LBT) is necessary. This demands, among other things, the installation of an inner lining over a length of 14 km in the second LBT tube, which is currently secured with shotcrete. As the second tube was excavated with a varying over-profile, a skillful choice in the sequence of formwork carriage geometries can lead to an optimization of the concrete volume to be installed, the feasibility of the build and the construction sequences, taking into account the excavation profile available.

In the spirit of a "proof of concept", the use of mathematical optimization algorithms for the automated determination of a cost-optimal sequence of formwork carriage geometries was analyzed in the section from km 31'500 to km 32'000. A reduced point cloud of a laser scan and geometric specifications of the formwork carriage geometry formed the basis of said algorithms. In addition, it was specified that the formwork carriage may only be adapted by the arrangement of a horizontal inlay in the apex.

Illustration: Planned installation of the inner lining

In order to later be able to use the cost optimization for the entire 14 km, special attention was paid to the best possible scalability in combination with an extensive modularization and automation. In comparison to the traditional manual optimization, the automated optimization approach developed in-house and adopted here resulted in a saving of approx. 1000 m³ concrete doe the 500 m tunnel and thus demonstrated significant advantages for costs, deadlines and resources.

Illustration: Visualization of a run of a 'particle swarm optimizer'

Services: Special civil engineering, geotechnical engineering, mathematical optimization, tunneling

Geotechnical engineering and foundation

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Jörg Meier
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References on the subject

SBB, Railway line CEVA, Geneva
Competence Center for Industry 4.0
Roche Building 10, Basel
Road tunnel in the vicinity of a recent slope slide
ASTRA N1, Zurich northern bypass, cut-and-cover Tunnel Katzensee, retaining walls, foundations, excavation pits