Aims

The aim of this project is to improve the understanding of processes at the mineral surfaces and interfaces between clay suspensions (excavated material) and cutting or conveying tools in mechanical tunnel construction. The interfacial processes are to be adapted by a selective manipulation of the surfaces to modify the mechanical properties of rocks. Chemo-mechanical coupling in clays refers to the change in engineering properties in a medium subjected to chemical changes. Common methods to reduce adhesion in tunnel construction are aimed at dispersing the clay particles. This causes problems in the re-use of the excavated material due to the prevention/reduction of the colloid formation. The colloid formation is an important process, with a major influence on the later structure and stability of the material. The project aims is the reduction of adhesion and/or repulsion between the mineral and the tool surface, whilst retaining the ability of clay particles to coagulate. A well-controlled (temporary) dispersion of the excavated material in the shield and subsequent manipulation for coagulation is also possible. This may favourably affect the long-term geotechnical properties with respect to the reuse of materials.

A: The clay particle was mixed with water and it keeps its compact structure. B: The same clay was mixed with ethanol. Due to the low dielectricity of the non-polar fluid, flocculation is caused Another important point includes a better prediction based on preliminary explorations of rock properties regarding stickiness. The proximate manipulation of clays shall then be adapted to the precise requirements of tunnel construction experiences regarding excavation and conveying processes. The applicability of the conditioning methods therefore needs to consider the geotechnical properties of the excavated material and its environmentally friendly behaviour during the subsequent dumping.