Abstract:

The rapid rehabilitation project on Guimiao Road in Shenzhen is 3 km long with the plane line of Shenzhen Metro Line 11. The floating deformation of the existing lower shield tunnel during foundation pit excavation should be controlled. Hence, on the basis of long-term automatic monitoring of the lower collinear metro shield tunnel during the construction period, the causes for deformation and floating of the underlying metro shield section are analyzed and determined by numerical analysis and calculation. And then the floating control technologies, i.e. ground reinforcement by triple-tube high-pressure jet grouting pile and triaxial mixing pile, adjusting the construction procedure of structure and adopting the split construction scheme, and construction of vertical shaft + anti-floating plate + anti-pulling pile in advance, etc., are put forward based on comparative analysis of the influences of excavation conditions, geological conditions, structural construction and excavation range and length on the floating deformation of shield tunnel, as well as the experience of floating control in project construction. The field practice shows that the measure of shaft + antifloating plate + anti-pulling pile is effective for the floating control of the shield section, which can ensure the operation safety of the lower metro shield tunnel during foundation pit construction.

Key words: cut-and-cover tunnel, deep foundation pit, collinear metro, shield section, floating control