Engineers are using ultrasonic and radar technology to develop custom restoration plans for the viaducts of the historic Waldbahn railway in southern Germany. The intent is to preserve the structures' appearance and reduce repair costs.

The Waldbahn railway, near Welzheim, is recognized as one of the most beautiful rail lines in the country and is listed as a national monument. However, some of its bridges, including the 100-year-old Laufenmühle viaduct, are showing major cracks in the reinforced concrete of their pillars and arches.

Construction of the Laufenmühle viaduct 100 years ago is considered to have been a masterpiece of civil engineering. Image credit: KITAndreas Gerdes, scientific director of the Karlsruhe Institute of Technology Innovation Hub, says that construction of the Laufenmühle viaduct was a "technical masterpiece of civil engineering.” However, current building regulations suggested that 30- to 50-cm-thick supporting concrete arches would need to be installed underneath the viaduct to buttress it. Doing so would have changed the appearance of the bridge.

Gerdes says that engineers used "modern scientific methods to improve the database and adapt the repair concept to the viaduct without damaging its basic structure.”

Using ultrasonic and building radar measurements, "every centimeter" of the viaduct was examined and documented to a depth of 50-70cm. Damaged points were identified and assessed and, using the picture that these measurements provided, engineers carried out computations to provide the basis for a customized repair concept.

For the Laufenmühle viaduct, this means that cement suspensions will be injected specifically into the damaged areas of the arched bridge in such a way as to preserve the viaduct's original appearance. Additionally, restoration costs will be reduced considerably—from €3.5 million ($3.71 million) to €2.2 million ($2.33 million).

Restoration of the viaduct is planned to be completed by summer 2017.