Multi-scale characterization of karst media, negative-pressure suffusion mechanism and collapse risk assessment for urban metro engineering: A case study of Guiyang metro line 3, China

Multi-scale characterization of karst media is a fundamental prerequisite for accurate stability evaluation and collapse risk assessment in karst terrains, especially for the safety control of urban metro engineering. Taking the Huaxi South Parking Lot of Guiyang metro line 3 as a case study, this paper proposes an integrated framework for karst collapse risk assessment by coupling multi-scale geological characterization, hydrodynamic-mechanical coupling simulation, and spatial multi-factor analysis. A comprehensive dataset, including 339 borehole records, core CT scanning results, long-term hydrogeological monitoring data, and laboratory test results, was collected to conduct multi-scale characterization of karst media across macro, meso and micro scales, reveal the vertical zonation of karst structures, clarify the hydrodynamic triggering mechanism of karst collapse, determine the critical instability threshold, and reproduce the entire evolution process of collapse. The results show that negative-pressure suffusion induced by rapid groundwater level decline, with a critical pressure difference of ≤ −190 kPa, is the dominant trigger of karst collapse in the study area. The lowest stratum stability and highest collapse risk occur in the strata with an overburden thickness of 2–5 m and a karst cavity diameter of ≥ 3 m. The high-risk zones account for 2.3% of the total study area, and are mainly distributed in the southern part, while the overall site remains stable under normal hydrodynamic conditions. This study can provide theoretical support and technical reference for karst collapse risk prevention and control in urban metro engineering.