Abstract
Crystallisation blockage in the tunnel drainage system will reduce the drainage capacity, thereby increasing the risk of lining leakage and cracks, and even endangering the safety of the tunnel structure. To avoid the serious impact of this disease, this study aims to reveal its formation mechanism and explore the effects and suitability of coating on preventing crystallisation. Therefore, we investigated and quantified the crystallisation blockage within the drainage system of the Nanla tunnel. On this basis, an indoor model test was built to study the anti-crystallisation effect and mechanism of coating. The results indicated that the crystallisation blockage primarily consisted of calcium carbonate mixed with small amounts of sediment and cement hydrates. It is mainly because of the corrosion effect of groundwater on shotcrete. Regarding the inner coating of the drainage ditch, it demonstrated a certain anti-crystallisation effect, with the hydrophobic coating exhibiting the best performance. Moreover, the microscopic results showed that the coating can achieve anti-crystallisation by lubricating the substrate surface and forming an unstable calcium carbonate form.
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