Sonar-Based Seepage Detection and Hydro-Thermal Modelling of Frozen Soil Curtain Evolution for Subway Cross-Passages in High-Permeability Strata
摘要
When constructing subway cross-passages in high-permeability strata via the mining method, the risk of water and sand inrush is prominent. The artificial ground freezing method serves as a core reinforcement technology, yet the uneven development of frozen soil curtains and closure failure induced by groundwater seepage remain critical engineering bottlenecks. To accurately reveal the coupling mechanism of seepage fields on freezing reinforcement, this study proposes a research framework of "multi-source measured data-driven and coupled numerical model validation". Sonar seepage detection was used to obtain the in-situ seepage velocity, flow direction, and spatial distribution of high-velocity seepage zones in the frozen area. Rather than being directly imposed as a fully spatially distributed seepage field, the sonar results were used to identify the dominant seepage direction and the maximum measured seepage velocity. Based on the most unfavorable engineering principle, the maximum measured seepage velocity was converted into an equivalent uniform seepage velocity of 1.0 m/d and adopted in the hydro-thermal coupling model.A three-dimensional hydro-thermal coupling model of porous media considering dynamic phase change characteristics is established using COMSOL to systematically simulate the evolution laws of temperature and moisture fields over a 40-day freezing period, with bidirectional verification conducted via on-site temperature measurement data to confirm model reliability. Results indicate: (1)Under the present freezing pipe spacing, brine temperature, soil properties, and freezing duration, a project-specific critical seepage velocity of approximately 2.0 × 10−4 cm/s was identified. When the seepage velocity exceeds this threshold, the risk of local thinning or closure failure of the frozen soil curtain increases significantly; (2) The coupling model exhibits high consistency with measured temperature data, with the temperature difference controlled within 5 ℃ after 25 days of freezing, enabling accurate characterization of curtain development; (3) Seepage causes uneven curtain distribution of "thicker upper and lower parts and thinner sides" through the mechanism of "differential cooling loss and accumulation", with the evolution process divided into four stages: "near-pipe nucleation—outward expansion—ring closure—thickening and stabilization".