Abstract
This project is based on a subway project in Shenzhen, which is constructed along the coast and primarily traverses sand layers, silty soil, completely weathered granite, upper-soft lower-hard strata, and rock-fill layers, with conditions including lateral crossing of bridge piles, high water pressure, and great burial depth. This paper addresses the challenges of shield tunneling under complex geological conditions and sensitive construction environments in coastal areas through systematic modifications to existing shield machines: (1) Upgraded composite cutterhead: adopting a six-spoke composite cutterhead with a 33% opening ratio, welding 6+6mm composite wear-resistant plates on the cutterhead panel, embedding alloy wear-resistant blocks around the cutterhead periphery, implementing a zoned tool layout, and equipping with shell cutters and overbreak teeth; (2) Added cutterhead freezing system: installing three-inlet three-outlet freezing circulation pipelines covering the entire cutterhead inside the cutterhead, forming a frozen soil curtain by circulating -30°C brine to freeze moisture in the soil ahead of and around the cutterhead, enabling atmospheric pressure tool changes under conditions where pressurized tool changes are not feasible; (3) Optimized 10bar sealing system: the main drive seal comprises internal and external sealing systems consisting of face polyurethane lip seals + axial polyurethane lip seals + axial rubber seals, which through automatic continuous grease injection can withstand working water pressure greater than 10bar by injecting EP2 grease without back pressure; (4) Improved slurry mode muck volume statistics system: installing flow meters and density meters on the slurry circulation pipeline, real-time calculation of actual muck volume per ring through an intelligent excavation management system, and conducting comparative analysis to avoid surface settlement caused by over-excavation. Through these modifications, key technical challenges including adaptability to complex strata, safety of adjacent construction, and high-water-pressure tunneling were successfully resolved. The research outcomes not only ensured safe and efficient project implementation, but also provided a replicable technical solution for shield machine selection and construction under similar geological conditions, promoting the application and development of composite tunneling modes in urban rail transit construction.
Full Text
Discussion on Targeted Modification Techniques for Dual-Mode (EPB/Slurry) Shield Tunneling Machines
Lan Anping
Guangzhou Metro Engineering Consulting Co., Ltd, Guangzhou 510000, China
Abstract
This study is based on a subway project in Shenzhen located in a coastal area. The project primarily traverses complex geological formations including sand layers, muddy soil, completely weathered granite, upper-soft lower-hard strata, and rock fill layers, while passing adjacent to bridge piles under conditions of high water pressure and great burial depth. Addressing the challenges of shield tunneling in such complex coastal geological conditions and sensitive construction environments, this paper presents a systematic modification of existing shield machines. The modifications include four key technical measures: (1) Upgrading the composite cutterhead: adopting a six-spoke composite cutterhead with a 33% opening ratio, welding 6+6mm composite wear-resistant plates on the cutterhead panel, embedding alloy wear-resistant blocks around the cutterhead periphery, implementing a partitioned tool layout, and configuring shell cutters and overbreak cutters; (2) Installing a cutterhead freezing system: arranging three-inlet three-out freezing circulation pipelines covering the entire cutterhead interior, which circulate brine at minus 30°C to freeze water in the soil ahead of and around the cutterhead, forming a frozen soil curtain that enables atmospheric pressure tool changes where pressurized conditions are not feasible; (3) Optimizing the 10bar sealing system: the main drive seal comprises inner and outer dual sealing systems consisting of face polyurethane lip seals, axial polyurethane lip seals, and axial rubber seals, which through automatic continuous grease injection using EP2 grease can withstand working water pressures greater than 10bar without back pressure; and (4) Improving the slurry mode muck volume statistics system: installing flow meters and density meters on the slurry circulation pipeline to enable real-time calculation of actual muck volume per ring through an intelligent excavation management system, with comparative analysis to avoid surface settlement caused by over-excavation. Through these modifications, key technical challenges including adaptability to complex strata, safety in adjacent construction, and high-pressure water tunneling were successfully resolved. The research findings not only ensured the safe and efficient implementation of the project but also provide a replicable technical solution for shield machine selection and construction under similar geological conditions, thereby promoting the application and development of composite excavation modes in urban rail transit construction.
Keywords: dual-mode shield; coastal proximity; large burial depth; unfavorable strata