Crystallization blockage in highway tunnel drainage system based on molecular dynamics

Crystal blockage in highway tunnel drainage systems often leads to a higher groundwater level behind the lining, leading to tunnel lining cracking and leakage. The drainage system mainly consists of circumferential, longitudinal, and transverse drainage pipes, as well as construction joint drainage waterstops. Most studies have carried out macro-experimental analysis on the crystal blockage of drainage systems, but few have been done at the micro-level. In this paper, the micro-laws between typical tunnel drainage materials and CaCO3 crystals at different groundwater temperatures were analyzed by the molecular dynamics analysis software. The results show that (1) CO32− and Ca2+ have the highest diffusion coefficients when the groundwater temperatures are 338 and 358 K, respectively. Under such conditions, it would be hard for them to form crystals. It is relatively easy for them to crystallize at 288 K. (2) When the groundwater temperature is higher than 318 K, the distance between CO32− and Ca2+ to crystallize is near 2.34 ± 0.05 Å. When the temperature is higher than 318 K, the distance is around 1.98 ± 0.05 Å. (3) Natural rubber facilitates the adsorption of CaCO3 aqueous solution at temperatures between 298 and 338 K. Polyethylene enhances adsorption at temperatures less than 298 K or higher than 338 K. (4) When the groundwater temperatures are 278 and 348 K, the adsorption occurred more easily at the interface between the CaCO3 aqueous solution and the calcite crystal. After CaCO3 is crystallized, it is more tightly bonded and is less likely to fall off from the polypropylene.