High Density Foams for Soil Conditioning in EPB-Tunnelling
To assure a homogenous face support pressure for EPB tunnel drives in closed mode, the soil needs to have a low permeability, suitable workability and plasticity. In this situation, the excavated soil acts as the support medium and helps to ensure a stable tunnel face and prohibits uncontrolled infiltration of water into the excavation chamber and the screw conveyor. Strongly varying coarse grained zones and cohesionless soils with low fine content doesn´t match to these requirements. Accordingly, such soils need to be treated with conditioning agents. Injection of foams in combination with polymers and slurries are used to add high amounts of fines with a low amount of fluid into the excavation chamber - all with respect to environment. The injected fines act as fillers and replace the missing fine content of the excavated soil. In this study, a newly developed soil conditioning technology, combining the impediment-free foam tube HDT-Montan Device CT and High Density Foams (HDF) was investigated. First laboratory tests focused on workability of the new technology in comparison to the conventional approach (separate injection of foam and slurry) to investigate workability of the conditioning technology and boundaries of HDFs.