Scaling in railway infrastructural drainage devices: site study

In France, about 450 km of high-speed lines (HSL) are potentially subject to drain scaling problem. A HSL site affected by calcite scaling was continuously monitored for 20 months to follow the phenomenon and also to estimate the monthly calcite precipitation rate. Drain water samples were also monthly analyzed and show high calcium and sulphate concentrations. The high sulphate concentration (~6 mM) highlights the dissolution of gypsum in the drain environment. Based on the material analysis (X-ray diffraction), gypsum is present in the subballast and capping layer. Since the drain system is a multi-environments system, and based on multi-phase reactions, the study is divided into two parts: a physical one (transport of water in the system) and a chemical one (transport of the reactants in the system). The physical processes have an essential impact on the chemical precipitation processes. In the present paper, on the basis of the collected data, the physical behaviour of the experimental site (water circulation) will be presented in the first step and used in the further chemical process study. The monthly calcite precipitation rate and quantities are given as well.