Objective Karst ground collapse is highly sudden, concealed, and difficult to monitor and warn against. This study analyzes the air-pressure response and precursory characteristics of covered karst collapse under vacuum-suction conditions.
Method Silty clay from a collapse area in Zhongliangshan, Chongqing, was used as the test material. Physical model tests were conducted under different groundwater-level drawdown rates and different moisture contents of the overburden. The dynamic variation of air pressure in the karst cavity during collapse was analyzed, and a precursor identification method based on critical slowing down theory was explored.
Result During groundwater-level decline, cavity pressure first decreased continuously and then released rapidly. A higher drawdown rate promoted faster negative-pressure accumulation and more readily induced collapse. Within an overburden moisture-content range of 30%-38%, lower moisture content corresponded to better airtightness of the overburden, making instability less likely. The autocorrelation coefficient based on critical slowing down theory captured collapse precursor information. At a moisture content of 38%, the precursor time window tended to shorten as the drawdown rate increased; however, under the same drawdown rate, the precursor time windows under different moisture contents did not show a monotonic pattern.
Conclusion Cavity air-pressure response and the autocorrelation coefficient based on critical slowing down theory can serve as reference indicators for predicting vacuum-suction karst collapse. The findings provide a methodological reference for precursor identification, monitoring, and early warning of this type of karst collapse.
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