Abstract: A semi-top-down excavation method is proposed for construction of an underground metro station, which is close to several high-rise buildings with shallow foundations and an elevated rail transit station. The efficiency of the new method to reduce the environment deformation is analyzed based on field measurements. The semi-top-down method combined the construction sequence of temporary strut and middle floor slab of the substructure during excavation, which united the advantages of both top-down method and bottom-up method. The settlement observation of the high-rise building and elevated rail transit station show that both the settlements and the differential settlement are within control, and the maximum settlement of the buildings, which is only 0.4 m far from the diaphragm wall, is less than 10 mm. After the middle slab is constructed, the increase of settlements trend to be mild, which means that the semi-top-down method has a good effect on controlling the surrounding deformation caused by excavation. Therefore, the new method can ensure the efficiency of deep excavation and reduce the environment-deformation.

Key words: deep excavation, settlement control, semi topdown construction, deformation