Investigation of calcite precipitation in the drainage system of railway tunnels
Résumé
Calcite precipitation causes clogging of barbicans and water gutters in drainage systems of railway tunnels, posing serious problems to railway tracks and subsequently to train circulation. In this paper, a number of tunnels, mostly in France, with calcite precipitation problems are identified. A first analysis of the problematic tunnels in France based on a geological map evidences the key role of the surroundings materials in the calcification phenomenon – it occurs in sedimentary rocks. For further analysis, an empirical index is defined allowing the tunnel calcification level (C-L) to be quantified and the main influencing factors to be analyzed. Results show that calcite precipitation depends not only on the hydraulic conductivity and CaCO3 content of surrounding rocks, but also on the nature of lining materials and the geometry of tunnels. As far as the potential mitigation solutions are concerned, removable geotextiles are proposed to be placed on the surface of gutters and replaced regularly. This new method is believed to be of high efficiency and low cost. It can be easily verified in the field conditions.