Abstract:  To investigate the deformation characteristics of foundation pit retaining structure in deep soft soil area in Foshan, China, and the applicability of the operation schemes, a case study is conducted on the monitoring data of seven typical metro stations in deep soft soil of Foshan urban rail transit line 3, and the variation laws of deep foundation pit horizontal displacement and displacement rate under various working conditions are summarized. Then, the influence of factors such as soft soil depth, support form, base reinforcement, and embedding depth on the deformation of retaining structure is examined. The practical results indicate that: (1) Three concrete supports are more beneficial to controlling the foundation pit deformation. It is recommended to further improve the construction technology level and fully consider the "timespace effect" of foundation pit excavation when using steel support. (2) The bottom of the foundation pit adopts the form of skirt + strip reinforcement, which is more conducive to controlling the deformation of the retaining structure. Increasing the embedding depth of the retaining structure is of little significance to deformation control. The reasons causing the phenomenon that the actual deformation of soft soil foundation pit is much larger than the theoretical value are further analyzed and the safety of the retaining structure is estimated, after which the control standard of the deformation value of the main foundation pit of the station (within 18 m) is proposed and the applicability suggestions for the selection of retaining structure under the condition of deep soft soil in Foshan area are given.

Key words: thick and soft soil, metro station, deep foundation pit, deformation characteristics, retaining structure, diaphragm wall monitoring