Methods

The project provides an important contribution to improve the efficiency in tunnel construction projects. First the interactions at the interfaces between tool and clayey rock / clay suspension have to be understood. A change in the structure through an active modification of the mineral surfaces allows a temporary or permanent influence on the geotechnical properties of the clay.

Tests to determine the adhesion of clays The mechanical properties of clay and clay suspensions are primarily determined by surface geochemistry and charge distribution at the interfaces, which in turn affect the arrangement of the clay minerals (structure). Due to the existance of physico-chemical effects, the pore fluid generally has a significant influence on the engineering behaviour of clays and thus the charge distribution can be externally manipulated. This has a corresponding effect on the structure and thus also the geotechnical properties of clay such as adhesion behaviour, porosity, sheare strength, consolidation, viscosity or water absorption capacity. Alternatively physical modification can also used, e.g. by applying electric voltage fields (electrokinetics) between the tool and clay suspension which can affect the adhesive behaviour of the tool. Through the application of an electric charge to the steel parts, water can be transported through the clay to the interface between the clay and the steel. This creates a film of water at the clay-steel interface and therefore reduces the adherence. Subsequently, these results may be used to adapt the active manipulation of the clay minerals to the relevant site conditions and industrial requirements. The interdisciplinary aspect of the project will allow research on all scales. The geoscientific knowledge of interfacial processes on a micro and nanoscopic scale will be linked to the engineering sciences knowledge of macroscopic processes, such as adhesion during mechanical tunnel driving. On this project seven institutions (three university departments and four industrial companies) will cooperate to achieve the results.

The department of Engineering Geology and Hydrogeology will be work on:

• realisation of different chemical manipulation methods (changing pH-value, variation of the dielectricity of the fluids, etc.),
• realisation of electrokinetic manipulation concerning practical tunnel construction experiences,
• understanding the chemo-mechanical properties of the clays.

The Clay and Interface Mineralogy department will:

• perform XRF (X-ray fluorescence analysis) for determination of the principal elements,
• perform research for characterizing the mineral surface (Measurement of Zetapotential, measurement of the exchange-isotherm, BET tests),
• manipulatation of the surface charge through cation substitution, e.g. by adding Na, Ca or Mg ions to the process water to alter the structure and coagulation behaviour.

The Geotechnical Engineering department will:

• process and evaluate project data,
• perform soil and rock mechanical laboratory and in-situ tests,
• develope bench-scale testing device to determine the adhesion,
• develope a classification scheme for the adhesion potential.

Herrenknecht’s tasks will be:

• provision of project data,
• collection and provision of material sample,
• cooperation in the derivation of criteria for a classification scheme,
• Design, construction and performance of pilot plant tests,
• derivation of criteria for manipulation methods under the specific requirements on the machine technology.

Züblin will provide:

• a web-based database for the processing of project related data,
• collection and provision of material samples,
• derivation of criteria for manipulation methods under the specific requirements on practical construction operations.

Condant’s work includes:

• provision of product and test data,
• provision of conditioning agents and additives,
• provision of the appropriate technology for the application to the laboratory tests,
• possibly modification and optimisation of the substances used,
• possibly cooperation in the development of new testing techniques.