Rehabilitation of a Tunnel From 1904 To Handle
Modern Heavy Goods Traffic
The Holzminde is a small river that flows through the center of the town of Holzminden in southern Lower Saxony, Germany. The town’s proximity to the “red water”, as the Holzminde is popularly referred to, has shaped its development over the centuries – and in 1904, one section of the river was diverted into a tunnel structure. This made it possible to create enough space for new traffic routes in the town center. The result was the construction of what is now the state highway L550.
Maintaining the Load-Bearing Capacity
More than a century later, the historic tunnel is once again the focus of an important infrastructure project: over the years, time had left its mark. The unreinforced tunnel structure which directs the Holzminde below the L550 for roughly 160 m was no longer able to comply with modern structural requirements for heavy load traffic. In order to restore the load-bearing capacity and reopen this section of the highway for heavy load traffic, extensive remedial actions were resolved on. For this purpose, the Lower Saxony Federal State Authority for Road Engineering and Traffic Development commissioned Spesa Spezialbau und Sanierung GmbH with reinforcement and rehabilitation of the tunnel.
New Reinforced Inner Lining
During the course of the work, a new reinforced inner lining made of in-situ concrete and sprayed concrete was constructed in the tunnel to provide the necessary stability for the future. This also considerably enhances the structure’s lifespan. Work had started in April 2025, completion was planned for March 2026. First the excavation and concrete demolition work was carried out to remove old and loose material. This was followed by the construction of excavation pits for the foundations. In early 2026, reinforcement works and formwork construction were underway, as well as concrete work for foundations and abutments using in-situ concrete. Work is concluded with the execution of the tunnel crown using the sprayed concrete method. With roughly 350 m³ of excavated soil and demolished concrete, 650 m³ of in-situ concrete, 1000 t of sprayed concrete and 120 t of reinforcement cages, this is a technically demanding project that requires precision and experience.
Confinded Spaces Required Precise Planning
The work was carried out in particularly confined spaces, which required precise planning of site logistics. From material delivery to removal of demolition materials and recoil during the sprayes concrete application, all processes had to be coordinated perfectly. And there are also particular requirements to fulfill: In the immediate work area, the channel of the Holzminde had to be covered in order to work safely, which in turn meant that the site had to be cleared immediately în the event of heavy rain. Another challenge was posed by the formwork sections, which had very large dimensions of 8 m, remarked Spesa Project Manager Lars Prokosch.
In November 2025, the project entered a key phase: The excavation pits were nearly completed, while the reinforcement, formwork and concrete work was simultaneously underway on the foundations and abutments. “Working on such an old structure is always something special. We are connecting the town’s historical past with modern construction methods – and helping to ensure that the infrastructure in Holzminden operates reliably in the future,” concludes Lars Prokosch. In spring 2026, the L550 will be fully reopened for heavy load traffic, and the Holzminde tunnel will be prepared to withstand many decades to come.
