Abstract:

During the twoway separate launching of the four largediameter earth pressure balance(EPB) in coastal shaft using steel sleeve, problems, such as limited launching space, low efficiency of separate launching construction organization, easy water and sand gushing when portal breaking, and easy floating of negative ring segment in steel sleeve, exist. Accordingly, a case study is conducted on the shield tunnel project between the Binhaixincheng station and the Airport station of the Binhai express line in Fuzhou, China. Targeted countermeasures, such as functional and spatial layouts of supporting trolley for shield, separate launching pipeline extension device, and downshaft horizontal transportation and marshalling, are designed and formulated to improve the separate launching efficiency of the four EPB shields. By improving the force and sealing system of the traditional launching steel sleeve, the reasonable force and effective sealing of the steel sleeve during the shield launching period can be ensured. The end reinforcement by threeaxis mixing pile + Ushaped wall is adopted to assist the precipitation to create conditions for the safe removal of the connecting wall at the portal. Technical measures, such as adding isolation wire brushes at the tunnel portal, optimizing the ratio of steel sleeve backfill and grouting, and adding negative ring embedded parts and welding, effectively control the floating of the negative ring segment in the steel sleeve. The technical measures recommended ensured the rapid and safe twoway separate launching of the four EPB shields using steel sleeves in the waterrich siltfine sand formation near the sea.

Key words: largediameter earth pressure balance shield, shaft, separate launching, waterrich fine sand stratum, pipeline transfer