Severe blockages of tunnel drainage systems greatly affect the lining structure of the tunnels, thus jeopardizing their stability and safety. In order to study the blockages of tunnel drainage pipes, the flow rate of a calcium carbonate crystal tunnel was measured in the mountainous area of Southwest China. According to the actual flow velocity results, numerical simulation was combined with finite element software (ANSYS Fluent). This analyzed the calcium carbonate crystallization near the interface of the tunnel drainage pipe. The results are as follows: (1) for both the Y-shaped three-way pipe and the T-shaped pipe, the values of maximum water velocity are similar but occur at different locations. At the interface of the transverse drainage pipes, flow velocity is the highest; (2) at the three-way joint segment, the water that flows in the longitudinal drainage blind tube is influenced by the water coming from the annular drainage blind tube. At the interface of the transverse drainage pipe, water flows at a lower speed in the Y-shaped three-way pipe than in the T-shaped pipe—the difference is about 3.75 times; (3) the smoothness of calcium carbonate deposition is correlated with water velocity and the content of calcium carbonate. The calcium carbonate crystal will occupy a larger space at locations with a higher calcium carbonate content and a lower flow velocity; (4) the drainage capacity of tunnel drainage pipes declines most when the volume fraction of calcium carbonate reaches 80%. Compared with the situation when calcium carbonate does not exist, the drainage capacity decreases by 84.78% for T-shaped pipe and by 77.64% for Y-shaped three-way pipe when the volume fraction of calcium carbonate is 80%.

Crystallization-induced blockages in tunnel drainage systems pose significant challenges to their functionality and longevity. To address this issue, this study proposes a novel adaptive drainage pipe designed to prevent crystallization. By constructing an indoor experimental model for anti-crystallization tests, combined with scanning electron microscopy (SEM) and molecular dynamics simulations, this study investigates the mechanism and effectiveness of the proposed system. The findings reveal that flexible PVC pipes in dynamic flow and expansion states significantly reduce crystallization compared to conventional PVC pipes. Among tested materials, EVA and TPU demonstrate superior crystallization resistance, with EVA exhibiting the lowest crystallization accumulation (7.13 g/m). Molecular dynamics simulations further elucidated the influence of material properties on the diffusion coefficient and binding energy of calcium carbonate crystals, with EVA showing the lowest binding energy with calcium carbonate at 135.11 kcal/mol, ultimately confirming EVA as the optimal material for crystallization prevention. These results offer new strategies and valuable references for managing crystallization in tunnel drainage systems.

The blockage of a tunnel drainage system has a significant impact on the stability and operation safety of a tunnel lining structure. In this paper, changes in the pore water pressure, stress and displacement of a tunnel lining under different blocking conditions are studied by means of indoor test and numerical simulation. The results show that the calcium carbonate crystallization phenomenon in the tunnel’s initial support concrete gradually appears with the passage of time, which leads to a decline in concrete quality and has a negative impact on its compressive strength and elastic modulus. The pore water pressure, stress and displacement increase with the precipitation of calcium carbonate crystals and the intensification of drainage system blockage. However, the influence of calcium carbonate crystallization on pore water pressure, stress and displacement is relatively limited within 40 days. The study provides a reference for tunnel construction in complex geological environments.