Abstract: When constructing a foundation pit with large spaces, existing buildings in the foundation pit should be protected. Based on a comparison between the central island and cut and cover top-down methods, a steel-strand tensioning method is proposed. The steel-strand tensioning method can be used in a case where the protected building (structure) has no basement or the basement is shallow, and the retaining structure should be a regular quadrilateral or hexagon; however, for deep basements, the steel-strand hooping method can be used, and the retaining structure should be round. Vertical support spacing can be reasonably adjusted according to the depth of the foundation pit and the deformation requirements of the protected building. When using the steelstrand tensioning method, the sleeve is used when drilling holes in the ground to reduce the settlement of the upper building. On the contrary, when the steelstrand hooping method is employed, 2~4 tension ends are provided, and channel steel is installed on the side of the retaining structure. The steelstrand tensioning method has many advantages, including convenient construction, low cost, and no influence on the underground space construction, which can be easily dismantled.

Key words: super-large foundation pit, approaching excavation, retaining structure design, central island excavation method, cut , and , cover top-down method, steel , strand tensioning method, steel-strand hooping method