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Cracks and Cavities due to Subsidence

Reconstruction of historic moat in Eutin, Germany

Today, reconstruction measures on municipal drainage systems are among the priority tasks of many local authorities. Frequently these drainage systems are historic structures.
In Eutin, in the Holsteinische Schweiz nature park, the municipality is currently carrying out extensive construction work on the local drainage system. Besides the construction of numerous new canals, the existing canal system is being strengthened.
A particular challenge here is the stonewalled moat, which not only connects the small and the large Lake Eutin but is also responsible for draining the major part of Eutin's historic old quarter, and which is severely affected by many years of subsidence.
The moat is a partly artificial and partly natural canal separating the urban area from the surrounding marshlands, which is why the town of Eutin never needed walls in order to protect its citizens from enemies. In the course of its historic development the moat was gradually overbuilt so that it literally vanished from the surface and is today located underground. Entire streets and buildings were constructed only a few decimeters above the vaults of the moat. Due to increasing development the strain on the foundation soil also increased, causing the interstitial and surface water to gradually escape from the grain structure of the foundation soil. This led to subsidence and decades of consolidation of the foundation soil. The subsidence resulted in the rearrangement of the stonewalled vault, giving rise to cavities in the structure and to leaks. Leaks and cavities were detected both in the base area and around the sidewalls. All this continually reduced the overall stability of the moat.
At the beginning of the reconstruction work, parts of the stonewalled canal were extensively reinforced and braced in order to ensure its long-term stability. The existing cavities were then initially filled with a cement suspension.
The question as to which material would be the best choice for the sealing injection under these conditions was answered taking into consideration the actual damage and the specific material properties.
The company in charge of the work opted for WEBAC® 1440. This PU injection resin is characterized in particular by its reactivity with moisture. Moisture in the structure results in the formation of many completely closed air pores in the fully reacted injection material. This allows for an optimum combination of flexibility and tightness.
The joints in the masonry and the surfaces between the filled cavities and vaults were thus sealed with WEBAC® 1440 and additionally stabilized after the cement suspension had set. The injection measures could be successfully implemented despite complicated and cramped conditions.