Causes, influencing factors, and prediction modeling of crystallization blockage of tunnel drainage blind pipe in non-karst area

Abstract

The complete functioning of the tunnel drainage system is critical in ensuring the stability of tunnel lining structures and safe operations. Therefore, the issue of crystalline blockage in the tunnel drainage system needs to be solved urgently. In this study, the formation mechanism of tunnel crystallization defects in non-karst areas was investigated, and the influencing factors of calcium ion dissolution of shotcrete were evaluated by field investigation. Also, the sampling analysis was carried out to determine the ionic composition and content of seepage water. The source and composition of crystallites were determined by X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and field-emission scanning electron microscope (SEM). The mechanism and role of pH in CaCO3 crystal formation were explored by simulation using MINTEQ 3.1 software. In addition, a new accelerated leaching test model was developed to examine the flow rate, concentration, and temperature effects on Ca2+ leaching rate in shotcrete. The analysis of water quality and crystal showed that the white and yellow crystals in the tunnel were calcite-type calcium carbonate, occurring as a paste. Micro-morphology of new crystals showed densely-distributed prismatic spherical and scaly crystal structure. The other parts were irregular squares, spindles, rhombuses, and other forms of scattered distribution. The Ca2+ originated from the shotcrete. The accelerated leaching test demonstrated that the optimal test conditions for the leaching rate of Ca2+ in shotcrete were a flow rate of 4 L/min, concentration of 5 mol/L, and temperature of 20 °C. Based on these findings, the prediction model of the Ca2+ leaching rate of shotcrete is established.

Keywords

• Tunnel drainage system
• Shotcrete
• Crystallization
• Calcium carbonate
• Ca2+ leaching