ABSTRACT In the last years the number of tunnelling projects in Europe increased considerably. Today the most common technique is mechanical heading with tunnel boring machines (TBM). In the course of tunnelling projects, often unexpected problems are encountered due to adhesion between clays and tool surfaces. Unfortunately, there is a lack of knowledge regarding the chemo-mechanical behaviour of the excavated material. As it is well known, the engineering behaviour of fine-grained soils depends mainly on the clay mineralogy of the soil. In first experiments Atterberg limits and vane shear tests have been performed with pore fluids showing different dielectric constants which were added to standard clays. These experiments were performed to investigate and quantify the impact of the dielectric constant of the fluids on the geotechnical properties of the different clay groups. All tests show that the mechanical behaviour is strongly affected by the dielectric constant of the pore fluids. Additionally, electro-osmotic experiments have been performed to investigate the effect of electric charge on the adhesion behaviour of the clay samples in order to reduce the adherence for a certain clay type. The adhesion behaviour of different clays has been also tested in newly developed cone pull-out tests.
SUMMARY Low-temperature oxidation (LTO) of magnetite is an alteration process which occurs under normal atmospheric conditions, causing maghemitization. The use of magnetic properties as palaeoclimate proxies requires improved understanding of how humidity and temperature affect such processes. We exposed natural magnetite, with grain size ranging from <1 to ∼30 μm, to different humidity conditions at room temperature and 70 °C for 1 yr. Changes in room temperature setups were very minor, but in all 70 °C setups alteration was detected by magnetic and mineralogical properties. Lowering of the Verwey transition temperature (Tv) turned out to be the most sensitive indicator of LTO, and also lattice constants correlate well with the shift of Tv. Thermomagnetic curves and XRD-results indicate that LTO affects the entire volume of the particles rather than only surface layers. The sample exposed to high relative humidity (rH) >90 per cent at 70 °C showed the strongest degree of LTO with an increase of the oxidation degree by ∼3 per cent according to Tv, and it was the only setup where partial alteration to hematite was indicated by Mössbauer analysis. The sample with extremely dry conditions (rH of ∼5 per cent) at 70 °C, and the sample that was exposed to cycles of high and low humidity in 2-weeks alternation at 70 °C, both revealed a smaller degree of LTO. The smallest change of the high temperature setups was observed for the sample with intermediate rH of ∼13 per cent. The results suggest a non-linear sensitivity of magnetite alteration to humidity conditions, high humidity strongly favours alteration, but alteration is strongly reduced when extreme humidity alternates with dry conditions, suggesting an importance of seasonality in natural weathering.
We present a novel approach for storing CO2 not only by hydrodynamic trapping within a reservoir but for converting it into the geochemically more stable form of calcite. The combination of CO2 storage and geothermal energy production is generally feasible because candidate sites are available, anhydrite is transformable into calcite and alkalinity can be provided by fly ashes or even in-situ. However, under the current circumstances the technology is not economical because the storable amount at depth is significantly less than one million tons over the life time of a geothermal heating plant.
