Scale deposits in tunnel drainage systems – A study on fabrics and formation mechanisms

摘要: Abstract Rapid deposition of chemical sediments, particularly calcium carbonate, is a widespread phenomenon in tunnel constructions, which can significantly disturb water draining. The removal the scale deposits drainage setting labor and cost intensive. Prediction or prevention these unwanted are challenging require detailed knowledge on their site-specific source, formation mechanisms environmental dependencies. This case study combines mineralogical, (micro)structural, isotopic, microbiological, hydrochemical approach to understand an Austrian motorway tunnel. Chemical isotopic results revealed that all investigated solutions originate from distinct local aquifer. High pH (11), indicative high alkaline element concentrations (Na 26 mg/l; K 67 mg/l), originated concrete leaching, strong supersaturation respect calcite (SI > 1) representative for scaling type 1. characterized by calcite, aragonite, rarely documented dypingite (Mg5(CO3)4(OH)2*5H2O), yields highly porous material showing minor indications microbial presence. In contrast, 2 strongly microbially influenced, yielding dense layered mineral deposits, typically consisting calcite. corresponding aqueous solution elevated Mg concentration (38 mg/l) molar Mg/Ca ratio (0.8). Scale containing aragonite precipitates next mostly growing pore spaces fabric, accounted as 3. Therein, always top needles, prior CaCO3 precipitation. composition shows highest (1.1). 4 compact deposit entirely Its exhibits 0.6. From obtained data sets conceptual model was developed describing operative (micro)environmental conditions responsible diversity deposits.