Abstract: Over 30 years of engineering experience in the Pearl River Delta water system have demonstrated that shield tunneling technology in composite strata offers remarkable technical superiority. This study systematically analyzes the geological properties of this region to determine the following: (1) the shallow strata consist mainly of soft soils from Quaternary Holocene paleochannel deposits; (2) the middle-deep strata feature a typical composite formation with soft soil interbedded with bedrock or weathered rock layers; and (3) the deep strata comprise various bedrock types, including granite, red beds (red sedimentary rocks), karst-developed limestone, and coal-bearing formations. The critical challenges encountered in shield tunneling through composite strata, specifically muck cake formation, muck gushing, and stagnant mucking, are investigated through the perspectives of engineering survey and design, equipment selection, and shield operation. The study assesses 12 typical engineering cases from three developmental phases of the technology: initial establishment, progressive development, and comprehensive upgrading. It summarizes the theoretical and technological innovations that have effectively addressed these challenges. Key achievements include (1) the establishment of a composite strata shield tunneling technical system in 2006, the introduction of a management principle for shield engineering, wherein “geology serves as the foundation, equipment acts as the core, and management is the fundamental guarantee”, and the formal definition of standardized terminology for risk management in composite strata shield tunneling, covering terms such as composite stratum, muck cake, muck gushing, and stagnant mucking; (2) the creation of a “six-element” selection principle and evaluation model for shields/tunnel boring machines; (3) the independent research and development of multimode shield machines; and (4) the innovative implementation of auxiliary construction methods for shield engineering, including key technologies such as shield pressurized chamber entry assisted by paste HDN muck conditioning agent, shield pneumatic-assisted excavation, and complete technology sets for metro shield tunneling in composite strata under water-rich karst conditions, as well as new environmentally friendly blasting techniques for hidden rock masses in composite strata shield tunnels. The key technical innovation priorities for shield tunneling in the Pearl River Delta water system are identified, focusing on shield mode selection, cutterhead and cutter configuration, slurry circulation system optimization, screw conveyor mucking system upgrades, tunnel design optimization, and complementary auxiliary construction technologies. Looking ahead, China’s shield tunneling technology will further advance in terms of formation adaptability, automation, and full-process intelligence. Innovations such as AI-assisted geological pre-prediction, intelligent mode switching for multimode shields, and large language model-enabled human-machine symbiotic intelligent tunneling control will be continuously refined through field applications. The expanding use of shield technology for small-curve, variable-diameter, and special-shaped tunnels will undoubtedly enhance China’s position in the global shield tunneling industry.

Key words: Pearl River Delta water system, composite strata, shield tunneling, shield type selection, boring mode