Permanent magnet treatment technology for crystal blockage of tunnel drainage pipes

The tunnel drainage pipes located in karst areas are oftentimes subject to crystallization and clogging derived from the calcification in groundwater, which would result in poor tunnel drainage during operation as well as subsequent issues such as cracking of the lining structure and seepage/leakage caused by rising levels of groundwater. To address the issue of crystallization in tunnel drainage pipes located in karst areas, we have examined the patterns of CaCO3 crystallization taken place in tunnel drainage pipes based on the intensity of the magnetic field, rate of water flow, and pipe materials. We have adopted the control variable method according to laboratory model experiments, X-ray diffraction, and scanning electron microscopy, and we have drawn reference from the principle of magnetic descaling applied in industry. Our research findings indicate that the mass of crystals in the drainage pipes would experience gradual increases and tend to stabilize with the test cycle, whereas the total mass of such crystals would decrease first before increasing with the intensity of the magnetic field. In addition, the mass of crystals was measured to be the smallest when the intensity of the magnetic field amounted to 0.2 T, whereas the rate of scale inhibition amounted to 30.78% of the crystal mass in the pipes without the magnetic field. Results of the micro-morphological analysis indicate that under the magnetic field, the CaCO3 crystals have been through the transition of its form from stable calcite to loose and unstable aragonite given that they are subject to the molecular orientation effect. The mass of crystals in the experimental pipes was found to increase in accordance with the test cycle and the increase of the water flow rate. In addition, under the intensity of the magnetic field amounting to 0.2 T, the final maximum mass of crystals in the pipe experienced a decline of 30.54% compared with that in the pipe under normal conditions. Judging from the experimental results, the materials applied in the steel-plastic composite pipe could, better address the issue of the weak magnetic field in some areas of the pipe to some extent, but they were unable to play a critical role in inhibiting crystallization. In general, the crystallization was found to be inhibited in those drainage pipes under the magnetic field, and the mass of crystals was to decrease correspondingly. Through this study, we aim to lay a foundation for the design, construction and re