Abstract: As underground engineering progresses toward greater depths, longer distances, and more complex geological conditions, the adaptability limitations of traditional singlemode tunnel boring machines have become increasingly apparent. Multimode tunnel boring machines have emerged as an inevitable solution for navigating complex geology. In this study, the primary design and construction technologies of multimode tunnel boring machines are  systematically investigated. The current applications of multimode tunnel boring machines in metro systems, municipal highways, urban railways, and other fields are summarized, focusing on recent advancements in critical technologies such as geology-equipment matching for adaptive selection, performance enhancement through targeted design for complex strata, efficient and reliable rapid mode-switching technology, and safe, high-efficiency construction techniques for special geological formations. Further, the extensive innovations in original, integrated, and collaborative development of multimode tunnel boring machines are highlighted. Current multimode tunnel boring machines still face technical bottlenecks in terms of intelligent mode-switching capabilities, switching efficiency, and long-term system reliability. To address these challenges, future development should prioritize three major directions: functional full-range capability, geological transparency, and equipment intelligence. Consequently, an integrated intelligent system spanning the entire "geological sensing-intelligent decision-making-precise control-feedback optimization" chain should be established, encompassing "design-manufacturing-construction" to drive technological upgrading and transformation in the tunnel boring machine industry.

Key words: dual-mode tunnel boring machine, three-mode tunnel boring machine, composite strata, tunneling mode conversion, special geological excavation technology