A lot of crystallizations exist on the inner wall of tunnel drainage pipes in Chongqing. Tunnel support structure often bears larger load than usual because the tunnel drainage pipes are blocked easily by the crystals and the groundwater level would rise. In order to investigate what the crystals are, site investigations and laboratory tests of crystals and groundwater were completed. Some valuable results have been obtained. Firstly, the crystallizations are usually discovered in drainage pipe exits of tunnels which are under construction in Chongqing. Furthermore, the results of XRD have confirmed that the crystals are calcite. And calcite morphology could be found in most SEM images. But there are other morphologies in these images other than calcite because calcite is often influenced by some factors, such as important ions in groundwater, pH of groundwater, kinetics effect, and so on. Finally, some steps and solutions to solve blocking of tunnel drainage pipes caused by crystallization are suggested. One of the best solutions is that some special materials which could prevent crystals from being attached to pipes are coated on the inner surface of drainage pipes. The results could contribute to understand the crystallization phenomenon profoundly and help solve the similar situations of tunnel drainage pipe blocking.

Tunnels located in cold regions are vulnerable to frost damage resulting from the special atmosphere, which directly threatens the safety of the tunnel structure and operation. Frost problems of tunnels in cold regions have not been fundamentally resolved. This paper reviews design theory and the frost mitigation techniques currently used in the design, construction and maintenance of cold region tunnels. The depths of freezing and thawing and frost heaving force are the key indexes of design theory. Insulation is the main design technology used to prevent frost heaving and thawing, and the active heating technology has also been applied in practice. In construction, reducing the heat of hydration and blasting by specific winter construction techniques can prevent tunnel freeze–thaw damages. In operation, the restoration of drainage systems, the reinforcement of structures and the reinstallation of freezing-prevention systems are effective measures to treat frost problems. Finally, some constructive suggestions and opinions are put forward to improve the service performance of tunnels.

If the tunnel drainage pipes are blocked, the supporting structures will be in danger because they would receive more force than before. In order to investigate the blocking problem, some laboratory tests and in situ experiments were carried out. Microtests showed that the main component of crystal is calcium carbonate. Calcium ions, carbonate ions, and bicarbonate ions of groundwater should be related to the crystal. The polyvinyl chloride pipe, hydrophobic antistatic self‐cleaning coated pipe, silicone rubber coated pipe, pipe under electromagnetic field, polytetrafluoroethylene coated pipe, and polyethylene coated pipe were used in laboratory and field experiments. The laboratory results showed that the electromagnetic field may be the best method to prevent crystallization because the crystallizing weight was less than 0.1 g in 30 days. The field tests showed that there was less crystals on the inner surface of hydrophobic antistatic self‐cleaning coated pipe than that of the polyvinyl chloride pipe and the polytetrafluoroethylene coated pipe. The crystallization prevention effects of the other experimental pipes need more studies to examine.

Grouting technology is an important method that has been widely adopted for the crack repair of tunnel lining, but the diffusion law of grouting slurry is still uncertain in tunnel lining cracks. For the sake of exploring the grouting diffusion law of tunnel lining cracks, this paper investigated the grouting diffusion shape and the relation between the diffusion radius and time with different crack widths in tunnel lining which by means of laboratory experiments and statistical analysis. Meanwhile, the diffusion equation of grouting in lining cracks has been established on basis of the grouting diffusion shape and experimental data. Furthermore, it is analyzed the correlation between the experimental values and the calculated values. The results revealed that the diffusion shape can be divided into a circular zone, excessive zone, and elliptical zone in the tunnel lining cracks, and the calculated values of the equation of grouting diffusion are highly correlated with the experimental values. Additionally, it is shown that the diffusion equation can accurately describe the relationship between diffusion radius and time of grouting in tunnel lining cracks. The study results would provide a theoretical basis for the prediction of diffusion radius on grouting repair for tunnel lining cracks.