Metro Tunnel Shield Construction in Highly Water-rich Karst Strata

［Objective］ When a shield tunneling machine passes through highly water-rich karst development regions in shallow strata, the presence of karst cavities poses significant challenges to land subsidence control, creating potential risks to the safety of adjacent structures. It is therefore essential to conduct research on metro tunnel shield construction in highly water-rich karst strata. ［Method］ Focusing on Shenzhen Metro Line 16 project, the risks associated with shield tunneling through highly water-rich karst strata are analyzed to address the impacts of karst cavities on tunnels and land subsidence. Numerical simulation analysis is performed using FLAC3D software, a shield machine tunneling model in this type of strata is constructed, and the relative positional relationship between karst cavities and tunnels as well as the influence of cavity developing scale on tunnels and land subsidence are explored. Key types and ranges of karst cavities requiring special attention during shield machine tunneling are identified. Finally, based on engineering analogy methods and actual project conditions, grouting measures for cavity treatment are proposed. ［Result & Conclusion］ Engineering practice verifies that karst cavity grouting measures effectively mitigate tunnel settlement and land subsidence issues caused by shield machine tunneling in highly water-rich karst strata.