ABSTRACT
When driving EPB shields, cohesive clayey and silty soils are suited best to support the tunnel face, provided having a sufficiently deformable consistency. In contrast, cohesionless, coarse-grained or very permeable soils without additional, often complex and expensive conditioning measures cannot be used as support medium. In highly permeable soils with ground water pressure, EPB shields may even reach their limit of applicability.
MC-Bauchemie in cooperation with Ruhr University Bochum have newly developed a highly flexible and cost-efficient system for conditioning very coarse ground. This new conditioning solution combines two existing approaches, 1) conditioning with foam and 2) addition of a High-Density Slurry containing a large amount of fines. This results in a new and flexible method, where a foam is produced from a High-Density Slurry. This High-Density Foam (SolidFoam™) could temporarily be used during the operation of an EPB-TBM, when driving through highly permeable soils or transition zones.
To introduce this new method of conditioning into tunneling practice, a series of laboratory tests regarding the reliable and practical production of SolidFoam™ were performed. The results include conditioning tests with coarse soil and SolidFoam™ to study the effects on the workability of the conditioned muck and on the reduction of its permeability to prevent undesired ground water penetration into the excavation chamber.
