On the Time-Development of Sulphate Hydration in Anhydritic Swelling Rocks

Anhydritic claystones are among the most problematic rocks in tunnelling. Their swelling has caused serious damage and high repair costs in a number of tunnels, especially in Switzerland and southwest Germany. The swelling is usually attributed to the transformation of anhydrite into gypsum. It is a markedly time-dependent process which might take several decades to complete in nature. The present paper focusses on simultaneous anhydrite dissolution and gypsum precipitation in a closed system, i.e. disregarding the transport processes that may also be important for the evolution of the swelling process. The paper begins with a presentation of the governing equations and continues with parametric studies in order to investigate the role of the initial volumetric fractions of the constituents and the specific surface areas of the minerals involved. A simplified model for the hydration of anhydrite is also proposed, which identifies the governing process and the duration of the swelling process. Finally, parametric studies are performed in order to investigate the effect of the anhydrite surface being sealed by the formation of gypsum. The latter slows down the swelling process considerabl

On the crystallisation pressure of gypsum

We estimate the crystallisation pressure of gypsum quantitatively, with reference to the geological context of the Gypsum Keuper formation. The formation contains sulphatic claystones which have the property of swelling in the presence of water and have caused substantial structural damage to the linings of several tunnels in Switzerland and Germany. The swelling of these rocks is attributed to the transformation of anhydrite into gypsum, which occurs via the dissolution of anhydrite in pore water and the precipitation of gypsum from the solution. This simultaneous dissolution-precipitation process happens because the solubility of gypsum is lower than that of anhydrite under the conditions prevailing after tunnelling, and it does not cease until all of the anhydrite has been transformed. The elementary mechanism behind the development of the macroscopically observed swelling pressure is the growth of gypsum crystals inside the rock matrix: If a crystal is in contact with a supersaturated solution, but its growth is prevented by the surrounding matrix, it then exerts a so-called crystallisation pressure upon the pore walls. In the present paper, the crystallisation pressure is calculated by means of a thermodynamic model that takes coherent account of all relevant parameters, including the chemical composition of the pore water and pore size. Variations in these parameters lead to a very wide range of crystallisation pressures (from zero to several tens of megapascals). By using the results of mercury intrusion porosimetry and chemical analyses of samples from three Swiss tunnels, however, we show that the range of predicted values can be reduced significantly with the help of standard, project-specific investigations

Information systems evaluation: Navigating through the problem domain

Information systems (IS) make it possible to improve organizational efficiency and effectiveness, which can provide competitive advantage. There is, however, a great deal of difficulty reported in the normative literature when it comes to the evaluation of investments in IS, with companies often finding themselves unable to assess the full implications of their IS infrastructure. Although many of the savings resulting from IS are considered suitable for inclusion within traditional accountancy frameworks, it is the intangible and non-financial benefits, together with indirect project costs that complicate the justification process. In exploring this phenomenon, the paper reviews the normative literature in the area of IS evaluation, and then proposes a set of conjectures. These were tested within a case study to analyze the investment justification process of a manufacturing IS investment. The idiosyncrasies of the case study and problems experienced during its attempts to evaluate, implement, and realize the holistic implications of the IS investment are presented and critically analyzed. The paper concludes by identifying lessons learnt and thus, proposes a number of empirical findings for consideration by decisionmakers during the investment evaluation process

Interpreting the evaluation of information systems investments Conceptual and operational explorations

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Rethinking the approaches to information systems investment evaluation

Numerous information system evaluation methodologies have been proposed in the literature. However, most of them suffer from a number of inherited disabilities originating in the nature of their fundamental principles as well as the nature of information systems evaluation. Uses evidence from the evaluation literature and two case studies to address the multiple dimensions for evaluation practices. We focus on the context, content and process of information systems evaluation as a source of organisational change. We found a noticeable gap between the recent theoretical work on IS evaluation and the practices within the case study organisations. This was not due to any lack of knowledge but was attributed to contextual variables such as the organisational culture and the power of important stakeholder groups

The Solubilities and Thermodynamic Equilibrium of Anhydrite and Gypsum

Anhydritic claystones consist of a clay matrix with finely distributed anhydrite. Their swelling has led to severe damage and high repair costs in several tunnels. Gypsum growth combined with water uptake by the clay minerals is the main cause of the swelling process. Identifying the conditions under which gypsum rather than anhydrite represents the stable phase is crucial for understanding rock swelling. As existing studies on the anhydrite-gypsum-water equilibrium appear to be contradictory and do not provide all of the information required, we revisit this classic problem here by formulating and studying a thermodynamic model. In contrast to earlier research, our model is not limited to the anhydrite-gypsum equilibrium, but allows for the determination of the equilibrium concentrations of the individual anhydrite dissolution and gypsum precipitation reactions that underlie the sulphate transformation. The results of the paper are, therefore, also valuable for the formulation of comprehensive sulphate-water interaction models that consider diffusive and advective ion transport simultaneously with the chemical dissolution and precipitation reactions. Furthermore, in addition to the influencing factors that have been considered by previous studies (i.e., fluid and solid pressures, concentration of foreign ions, temperature), we consistently incorporate the effect of the surface energy of the sulphate crystals into the thermodynamic equations and discuss the effect of the clay minerals on the equilibrium conditions. The surface energy effects, which are important particularly in the case of claystones with extremely small pores, increase the solubility of gypsum, thus shifting the thermodynamic equilibrium in favour of anhydrite. Clay minerals also favour anhydrite because they lower the activity of the water. The predictions from the model are compared with experimental results and with predictions from other models in the literature. Finally, a comprehensive equilibrium diagram is presented in terms of pore water pressure, solid pressure, temperature, water activity and pore size

Information systems evaluation as an organizational institution - experience from a case study

Information systems evaluation has strong social and organizational dimensions while existing research focuses primarily on the formal and positivistic characteristics. We investigate the organizational roles of the key stakeholders within the particular evaluation context (orientation). We focus on four evaluation orientations: control, sense-making, learning and exploratory. Experience from a case study is used to analyse these concepts and relations. The case organization attempted to move from a state of an ad-hoc evaluation practice to a more business-driven one. New tools, processes, roles and responsibilities were developed during the attempt. We examine the behavioural and organizational integration aspects of evaluation during that journey