In the last years the number of tunnelling projects in Europe increased considerably. Today the most common and efficient technique is mechanical heading with tunnel boring machines (TBM). In many cases, in the course of large projects, unexpected problems could be encountered due adhesion between clays and tool surfaces, such as blocking of excavation tools and clogging of screw or belt conveyors. One of the most important factors to successfully reduce the clay adhesion is the use of special polymers and foams. But why does the clay stick exceedingly to the metal parts? Unfortunately there is a lack of knowledge regarding the chemo-mechanical behaviour of the excavated material. Aim of the project is to provide knowledge and methods to identify possible adhesion problems in the preliminary phase of a tunnelling project and to provide a selection of suitable methods to cope with this problem with a minimum of negative side effects. This will have an overall positive effect on the efficiency, sustainability and profitability of projects.

Clay attached to the cutting wheel of a TBM.

Aims

Since there is scarce information about the chemical-mechanical coupling of the clay, several tests will be carried out on fine-grained material to better understand the mechanical behaviour of the clays. Subsequently, the findings will be used to observe the effective change in adhesion forces. Some new experimental set-ups are tested, considering as well tensions as torsion and shear stress to provide information about adhesion as well as cohesion of the material.

1: The clay particle was mixed with water and it keeps its compact structure. 2: The same clay was mixed with ethanol. Due to the low dielectricity of the non-polar fluid, flocculation is caused

Methods

As the engineering behaviour of clays depedens many parameters (e.g. mineralogy, porosity, sheare strength, consolidation, viscosity, water content), several tests will investigate the influence of different pore fluids (e.g. ethanol, acids and bases) on the change of the mechanical parameter (e.g. cohesion, shear resistance). As the modification of the mineral surfaces can be achieved also physically, (electrokinetics), several tests will be performed to understand the response of the different types of clays on different electric charge. The interdisciplinary aspect of the project will ensure research on all scales. The geoscientific knowledge of interfacial processes on a micro- and nanoscale will be linked to the engineering sciences knowledge of macroscopic pro-cesses, such as adhesion phenomena during mechanical tunnel driving.