Rheological Properties of Liquid and Particle Stabilised Liquid Foam
Aycan Özlem Özarmut and Holger Steeb
aydin@lkm.rub.de, holger.steeb@rub.de
Institute of Mechanics, Ruhr-University Bochum, 44801 Bochum, Germany
In Earth-Pressure-Balance (EPB) tunnelling, the surface settlements may be prevented by using excavated
ground as face support medium, controlling ground movements and ground water flow into the excavation
chamber. The excavated ground (soil) does not exhibit suitable conditions to be used as support medium.
A suitable condition for the excavated soil can be achieved by mixing conditioning agents that are mainly
foams. To ensure a homogeneous pressure transfer onto the tunnel face, the conditioned soil, i.e. the soilfoam mixture, requires a certain effective viscosity. This is also important for an effective transport through
the excavation chamber. Understanding the rheological properties of the (added) foam and the foam-soil
(foam-particle) mixture, and its influence on the soil is not possible without advanced experimental
investigations. Therefore, various rheological experiments such as flow curve tests, oscillation tests, and
further experiment to determine the effective yield stress are performed. In detail, (homogeneous)
rheological experiments are performed by using plate-plate and cone-plate geometries with modified, i.e.
rough surfaces in order to prevent slip effects. Since the microstructure of the foam accounts for the
effective rheological properties of the complex fluid, the size, shape and distribution of the foam and
particle-laden foam is characterized in detail by imaging techniques. In order to perform the above
mentioned experiments, polymer-stabilised shaving foam seems to be a good choice in laboratory tests
due to its time stability and easy accessibility. On the other hand, glass beads (of different diameter and
volume fractions, i.e. specific surface areas) are used to understand the effective material behavior of
foam-particle mixtures. The experimental results are compared with rheological yield-stress models of
Herschel Bulkley type.
Keywords: EPB tunneling, soil conditioning, foam, rheological experiments, Herschel Bulkley model
Oral presentation (20 minutes)