Field monitoring and analysis of effects of metro tunnels under historic buildings

Two historic buildings are subjected to the impact of nearby excavation and underlying tunneling, which has to be strictly controlled. Countermeasures include ground sleeve valve pipe grouting, top-down method of metro station excavation, diaphragm cut-off wall of confined water, freezing method outside the end well, and optimized parameters of shield tunneling. The settlements of the historic buildings induced by underlying tunneling, dewatering and excavation of nearby underground metro station , freezing and grouting outside end well are measured and analyzed. The field measured data show that the settlements of buildings can be minimized by applying the optimized shield tunneling parameters. Leakage during the construction of horizontal freezing hole and tunneling may cause significant settlement of overlying buildings. The building with large weight can hardly be lifted by grouting when there is soft clayey soil layer between building foundation and grouting. While the building with small weight can be lifted under such conditions. However, the rise of the building can be part offset by the consolidation of soft clayey soil due to the dissipation of the excessive pore water pressure generated during grouting. Freezing zone is vital to leakage prevention during tunneling in the freezing zone before the shield enters the end well. The effect must be evaluated, especially before the large jack force is adopted to advance the shield.