Electro-chemo-mechanical manipulations of clays regarding the clogging during EPB-tunnel driving

Abstract During mechanical headings with tunnel boring machines (TBM) in clay-rich soils, the exavated material often sticks to the cutting tools, cutting wheel or conveying system. This may cause great difficulties in the excavation, transport, reuse or dumping of the excavated materials, as well in the general construction progress. The causes for this are mainly adhesion processes that occur at the interfaces and at surfaces of the clay minerals and tools. In the course of this research, methods for quantification, as well as appropriate countermeasures to deal wit the problem o the stickiness of the geomaterials and subsequent clogging were investigated. To this end, the geoscientific knowledge of interfacial processes and manipulation techniques on a micro- and nanoscale has been linked to the engineering sciences knowledge of macroscale processes. Several geotechnical laboratory tests, clay mineralogical investigations and electrical charakterization of the fine-grained materials have been performed. The resuslts show that the chemo-mechanical properties of the clays are dependent not only on the pore fluid chemistry but also on the mineralogical compositions. The variation of the geotechnical characteristics is useful to modify the internal cohesion of the material and act indirectly to modify the adhesive forces of the clays. C-potential measurements were performed based on three different models in order to find a correlation with the mechanical/adhesive properties of the clays. Electrical experiments also show that the application of an electrical field reduces the stickiness of the clays to a metal surface but causes some unwanted effects. However, the resuslts of this research might help to improve the prediction of problems that can be expected with reactive geomaterials on the basis of preliminary investigations for tunnel projects.