Design and monitoring analysis of deep foundation pit of super-large subway station adjacent existing section tunnel

Xiaoyangjiang Station of Ningbo Rail Transit Line 7 is a multi-line transfer station with a three-storey underground. The length of the foundation pit is 270.8 m, the width of the foundation pit of the four line sections is 51.4~55.7 m, the width of the foundation pit of the two line sections is 19.6~27.3 m, and the depth of the foundation pit is 27~31 m. The station construction site is located in an area with deep soft soil and is 30.8 m away from the adjacent section tunnel, which has high requirements for foundation pit deformation control. To control the deformation of the foundation pit and the adjacent tunnel, the foundation pit support design adopts the diaphragm wall + internal support system, and adopts a series of measures such as hard pit time-sharing and section construction, soft pit layered excavation, lengthening the diaphragm wall structural section to cut off the confined water layer, and setting up construction access roads and trestles. The monitoring results show that the deformation control of the large external corner of the foundation pit is very effective by using soft pit division and layered excavation; The surface settlement is sensitive to the load outside the pit, and the surface settlement in the area with long-term load outside the pit is much larger than that in the other areas; The excavation of foundation pit has an impact on the adjacent section tunnel. When the excavation depth is less than the tunnel buried depth, the impact on the section tunnel is greater, while when the excavation depth exceeds the tunnel buried depth, the impact on the section tunnel is relatively small. The final settlement of the section tunnel is 5.9 mm, which is controlled within the allowable range.