STUVA research wins Tunnel Day Innovation Award

With their development, STUVA and its research partners have succeeded in exploiting the cost advantages of monocoque tunnel construction even at higher water pressures.
Until now, segment tunnels with monocoque construction have mostly been designed pressure-tight, whereby sealing is carried out by means of sealing frame profiles. From a water pressure of around 5 bar, however, a much more complex and expensive double-shell construction with an additional drainage layer between the inner and outer shells had to be used so far. With the newly developed pumpable annular gap material, this is no longer necessary as it has a sufficiently high permeability to be used as drainage.
The core idea of the development is the defined foaming of cement suspension by means of a foam generator to achieve an open-pored and water-permeable structure with sufficient strength to guarantee the segment bedding. In the test halls of STUVA, a suspension formulation and the exact dosage of the admixtures were therefore determined and tested in extensive test series on a specially designed test rig for annular gap mortars. Strict specifications for processability, pumpability, stability as well as water permeability and compressive strength of the material were applied. In addition, investigations on the sintering behaviour were carried out to ensure the durability of the material.
The innovative annular gap material has several substantial advantages:

• Further resource conservation through less aggregate grain size and cement
• Improved environmental protection through smaller excavation cross-section (less excavated material, less landfill space)
• Increased safety, because there is no danger from flying packers (no bubbling of pearl gravel)
• Shorter construction time by dispensing with additional inner lining (manufacture in one operation)
• Extension of the application range of segment tunnels in solid rock due to lower fissure water pressures (simpler sealing)

The general suitability of the ring gap material developed was proven not only in the series of laboratory tests, but also in construction site tests. In the meantime, the results have been applied for a patent. 

• 28.07.2016 New test stand for annular gap mortar