Dolomite is a soluble salt rock, and in dolomite locations, tunnel drainage systems are frequently clogged by crystallisation, resulting in tunnel leaks. This research starts with a field survey to investigate the environmental conditions that influence crystal formation and sample collection. Afterward, the crystals underwent examination using EDS, scanning electron microscopy (SEM) and XRD, which enabled the analysis of crystals' elemental composition, matter composition and microstructure. Finally, a measure for crystal removal using ultrasound is proposed. The feasibility of ultrasonic crystal removal was verified by the indoor model experiment. The results show that the crystals contain mainly metallic elements such as Ca, Mg and Al. The main component of the crystals is CaCO3. The crystals also contain small amounts of Mg (OH)2, Al (OH)2 and CaAl2(SO4)3(OH)2‐26H2O. As the ultrasonic frequency increases, the de‐crystallisation effect becomes more pronounced. At ultrasonic frequencies greater than 50 kHz, the growth in crystal break‐up efficiency tends to level off. Therefore, the ultrasonic frequency based on this parameter will be used to remove the crystals.

Tunnel seepage is one of the most common pathological disasters in tunnel engineering. Drainage pipes (ditch) caused by crystallization blockage emerge in an endless stream, especially in tunnels built in soluble rock areas such as dolomite and limestone, which it is one of the causes of water leakage, so it is of theoretical and practical significance to explore the factors and mechanisms of crystallization in the drainage system of dolomite tunnels. To study the crystallization blockage law of mixed solution in the drainage system of dolomite tunnels, based on the on-site geological survey, water quality inspection, and indoor model test, the crystallization blockage law of mixed solution in the drainage system was explored, and the classification of crystallization blockage was proposed based on the test. The test shows that: First, the crystallization blockage of the water outlet of the vertical drainage pipe (longitudinal pipe) and the horizontal drainage pipe (horizontal pipe) is more serious, while the crystallization blockage of the annular drainage pipe (ring pipe) is less. Second, the Cl–K+-Na+ ion coupling concentration will affect the crystallization, and the pipe crystallization is also positively correlated with the CO32--SO42--Ca2+-Mg2+-Al3+ ion coupling concentration. The higher the concentration, the more crystallization, and the crystal growth law The performance is fast and then slow. Third, the evaluation of the blockage degree of the vertical tube, the horizontal tube, and the ring tube shows that the amount of crystallization per linear meter of the horizontal tube is more, and the degree of crystal blockage is higher, while the degree of crystallization of the vertical tube is between the horizontal tube and the ring tube. Fourth, after preliminary construction of the classification model and classification theory of crystallization blockage in drainage pipes, indexes such as classification coefficient l, blockage height H, and surrounding rock pressure σ are calculated. Based on the quantitative indexes, the classification of crystallization blockage degree is proposed. The crystal blockage of the tunnel drainage pipe is divided into four grades: complete blockage, severe blockage, moderate blockage, and mild blockage.