The excavation and pit support are the problems that must be solved during reconstruction and extension of the subway stations of existing line built in 1974

which was part of line No.1 of Tianjin Metro system. Because of soft ground

pre-grouting is needed to reduce the displacement and settlement of the station box due to deep excavation and back filling

and also to control ground water ingress. These stations are right under the main streets and the heavy traffic in the streets makes the work very difficult. The possible construction operations to control station box and ground displacement and minimizing the effect due to reconstruction on the traffic are researched; some suggestions are given .