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.

The crystalline blockage of tunnel drainage pipes in a karst area seriously affects the normal operation of drainage system and buries hidden dangers for the normal operation of the tunnel. In order to obtain the influencing factors and laws of tunnel drainage pipe crystallization in a karst area, based on the field investigation of crystallization pipe plugging, the effects of groundwater velocity, drainage pipe diameter, drainage pipe material, and structure on the crystallization law of tunnel drainage pipe in karst area are studied by indoor model test. The results show that: (1) With the increase of drainage pipe diameter (20–32 mm), the crystallinity of drainage pipes first increases and then decreases. (2) With the increase of water velocity in the drainage pipe (22.0–63.5 cm·s⁻¹), the crystallinity of the drainage pipes gradually decreases from 1.20 g to 0.70 g. (3) The crystallinity of existing material drainage pipe is: M3 (poly tetra fluoroethylene) > M2 (pentatricopeptide repeats) > M4 (high density polyethylene) > M1 (polyvinyl chloride); M8 (polyvinyl chloride + coil magnetic field) is used to change the crystallinity of drain pipe wall material. (4) When the groundwater flow rate is 34.5 cm·s⁻¹, M1 (polyvinyl chloride) and M8 (polyvinyl chloride + coil magnetic field) can be selected for the tunnel drainage pipe. The research on the influencing factors of tunnel drainage pipe crystallization plugging fills a gap in the research of tunnel drainage pipe crystallization plugging. The research results can provide a basis for the prevention and treatment technology of tunnel drainage pipe crystallization plugging.

The occurrence state of groundwater in a karst area has a significant impact on the tunnel lining structure. The impact on the groundwater is more significant during construction. This paper used numerical simulation to study the grouting reinforcement range of the Liaoshan Tunnel. This was based on the critical water rich height. Under Grade IV and Grade V surrounding rock, the critical points of grouting reinforcement were 230 m and 240 m deep, respectively. The vertical and horizontal stress and seepage flow of the tunnel arch crown and invert decreased as the circumferential grouting reinforcement range increased. In the case of no grouting reinforcement, 1/4 circumferential grouting reinforcement, 1/2 circumferential grouting reinforcement, and all circumferential grouting reinforcement, the seepage flow was 7 m³/dm, 4 m³/dm, 3 m³/dm, and 0 m³/dm, respectively. With Grade V surrounding rock, when the groundwater level was 260–270 m away from the tunnel arch crown, two schemes could be adopted: 1 m radial grouting reinforcement and 1/2 circumferential grouting reinforcement. The results have guiding significance for developing a construction scheme of a karst water rich tunnel.

Drainage pipe blockage resulting from crystals is one of the causes for cracking and leakage of tunnel lining. Therefore, effective prevention from drainage pipe blockage caused by crystals is crucial to ensure the safety and stability of lining structures during the operation of tunnel drainage system. Based on a large number of indoor model tests and numerical simulation analyses, binding energy between four materials and the calcium carbonate aqueous solution (“solid + liquid” system) and that between the four materials and the two typical growth crystals of calcium carbonate (“solid + solid” system) were studied. The research results indicated that: (1) The four materials all had an adsorption effect on the calcium carbonate aqueous solution system, and the PA6 had the greatest adsorption effect while the PP had the smallest adsorption effect; (2) There was spontaneous adsorption between the PVC or PA6 and the two typical growth crystals of calcium carbonate and no adsorption between the PP or SiC and the two typical growth crystals of calcium carbonate unless external energy was in place; (3) The PP and SiC can be used as the materials for drainage pipe flocking, but it shall be ensured that the fluffy material has a good geometrical property. The prevention technology for crystallization that causes drainage pipe blockage fills the gap in the research of drainage pipe blockage caused by crystals, which can reduce the maintenance cost for the operation of the tunnel drainage system and ensure safe and normal operation of the tunnel.

With the rapid development of traffic infrastructure in China, the problem of crystal plugging of tunnel drainage pipes becomes increasingly salient. In order to build a mechanism that is resilient to the crystal plugging of flocking drainage pipes, the present study used the numerical simulation to analyze the two-dimensional flow field distribution characteristics of flocking drainage pipes under different flocking spacings. Then, the results were compared with the laboratory test results. According to the results, the maximum velocity distribution in the flow field of flocking drainage pipes is closely related to the transverse distance h of the fluff, while the longitudinal distance h of the fluff causes little effect; when the transverse distance h of the fluff is less than 6.25D (D refers to the diameter of the fluff), the velocity between the adjacent transverse fluffs will be increased by more than 10%. Moreover, the velocity of the upstream and downstream fluffs will be decreased by 90% compared with that of the inlet; the crystal distribution can be more obvious in the place with larger velocity while it is less at the lower flow rate. The results can provide theoretical support for building a mechanism to deal with and remove the crystallization of flocking drainage pipes.

Shotcrete has the advantages of short setting time, high early strength, simple process and flexible operation methods. It is mainly used as temporary support in domestic highway tunnels. This study investigates the development of low-rebound shotcrete for tunnel construction by adding silica fume and fly ash into the mixture. Sandstone and limestone were employed to simulate the surrounding rock. The workability and mechanical properties of the shotcrete were evaluated based on slump tests, rebound rates, compressive strength measurements, and bonding strength tests between the surrounding rock and the shotcrete. Furthermore, the research investigated construction techniques, with an emphasis on spraying distance, shrinkage angle, and wind pressure, and optimized these parameters for practical engineering uses. The outcomes demonstrate that the addition of silica fume enhances the mechanical properties of the shotcrete and reduces rebound. It was discovered that optimal spraying distance was between 1.2 m and 1.5 m, with the optimal wind pressure at 0.5 m, and the ideal shrinkage angle at 6°. Research on low rebound shotcrete is of great significance for improving construction quality, construction efficiency and engineering structural performance, and also meets the requirements of sustainable development.