Crystallization-induced clogging in tunnel drainage systems: Mechanisms, prevention, treatment, and case studies

Extensive studies have been conducted worldwide on crystallization clogging in tunnel drainage systems, yielding a series of important findings. This paper systematically reviews the research progress on the formation mechanisms, prevention, and treatment technologies of crystallization clogging in tunnel drainage systems. By integrating the innovative achievements of our team in this field with a representative engineering case from the Dongtianshan Tunnel Project in Xinjiang, the current research progress and engineering application prospects of this issue are discussed. Based on the spatial distribution characteristics and temporal evolution patterns of crystallization deposition in tunnel drainage systems, a three-level system framework is established to explain the influencing factors and evolutionary features of crystallization clogging. On this basis, a dual-path prevention concept involving front-end source control and back-end process regulation is summarized. Existing prevention and treatment measures are further reviewed from multiple aspects, including shotcrete composition optimization, drainage system design and construction improvement, pipeline coating, the application of physical fields, and the use of scale inhibitors. Meanwhile, the existing technical bottlenecks and engineering challenges are analyzed from five perspectives, namely crystallization clogging mechanisms, design and construction, materials, detection and monitoring, and treatment methods. The review shows that major challenges remain in the long-term evolution of calcium leaching from shotcrete, microscopic crystal nucleation mechanisms, the durability of preventive materials, intelligent detection and monitoring technologies, and the development of efficient and environmentally friendly treatment methods. These findings provide valuable references for mechanistic studies, technological innovation, and engineering practice related to crystallization clogging in tunnel drainage systems.