ABSTRACT
The application range of slurry shield machines aims primarily non-cohesive soils. In addition, slurry shields are preferably utilized in tunnelling projects with challenging ground conditions, e.g. coarse and highly permeable soils, extremely heterogeneous geology as well as very high ground water table. These boundaries impose particularly high requirements on the support fluid. Here, bentonite suspensions are applied, which are characterised by the rheological parameters yield point and viscosity. For special applications, further characteristics and quality standards are important, e.g. density and the interaction with the in-situ soil at the tunnel face. In this paper, the fundamental rheological parameters of bentonite suspensions are discussed, including widely used measuring devices such as the Marsh-funnel, ball-harp rheometer and rotational viscometer. The parameters gained from these devices are supplemented by advanced rheometric tests. The measurement profiles provide further information on the flow behaviour. As an example, the flow curve is a valuable tool to constitute the yield point and the fluid flow under very low and high shear rates. This extended analysis allows a detailed discussion within the suspensions design phase. Finally, the suspension requirements are summarized and related to practical experience for the needs of a construction site. These settings are transferred to suitable suspension design supported by the findings of research work and laboratory test.
