Tuesday, September 07, 2021

Der Tunnel - Verbindungsbahn der S-Bahn Stuttgart

It's rare that railroad projects are documented in vast detail from the perspectives of civil engineering, economics, and social impact in a single book. "Der Tunnel" is one of the exceptions. It describes design and construction of the central element of the S-Bahn Stuttgart: The city tunnel between Hauptbahnhof (main station) and Schwabstrasse, and it's underground continuation to Vaihingen via Universität. In over 35 detail-loaded chapters the authors work through early plans and financing of the project, discuss in detail the various construction sites within the city core, including engineering challenges of constructing a tunnel in the middle of a bustling city with difficult geology. They keep the high level of detail as they discuss the concerns and engineering challenges building the Hasenbergtunnel towards Vahingen.

Along the way they touch on such diverse topics as re-routing of sewers, tram lines, and car traffic; digging next to, or under, historic building; construction impact litigation; project financing; operational aspects resulting from tight headways of S-Bahn trains; supply and material logistics; geology of Stuttgart's underground; triangulating underground with high accuracy and verifying construction to plan; etc. etc. etc.

Hamburg method vs. Berlin method of open tunnel construction - spot the difference!

In addition to the general civil engineering aspects of the project, what I found most interesting are the many descriptions of when things were built differently than originally planned, or when things went wrong unexpectedly and what to do about it. Above is an example of how a different tunnel construction method was chosen in Rotebühlstrasse near Feuersee to get a narrower construction site and gain just under two meters extra space between the construction site and buildings lining the street to facilitate surface traffic and building access.

The book has answers for civil engineering questions I asked myself when riding the train. E.g. the lower half of the Hasenbergtunnel is constructed as two single-track tunnels that merge to a single two-track tunnel in the upper half towards Universität. You can hear the difference as the tunnel transitions when riding the train between Schwabstrasse and Universität. The reason is due to geology. The lower half of the tunnel lies in keuper gypsum ("Gipskeuper") which can develop a lot of pressure on the tunnel bores due to swelling of the gypsum in combination with water. Constructing two smaller circular bores made it simpler and more cost-effective to provide for the necessary fortification of the tunnel against rock pressure in this stratum. In the upper part of the tunnel, the gypsum over time has been washed out from the keuper rock and thus it can't develop the same amount of rock pressure on the tunnel bore. Building a larger diameter two-track tunnel was more economical in this section.

While I was studying at Universität Stuttgart, I used the infrastructure described in this book daily, so I -- along with many others that lived and live in the Stuttgart area -- have developed a special relationship with the S-Bahn. We use it daily and take it for granted. This book is an interesting look behind the scenes of what goes into such major infrastructure projects, and also provides historical perspective on changes in planning and construction methods during the early 1970's and early 80's, a period of transition towards a computerized world. 

"Der Tunnel" (ISBN: 3-925565-01-9) is written in German, was published in 1985, and can occasionally be found secondhand on abebooks, booklooker, or other sources for antiquarian books.

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