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Case Study of Active Deformation Control for a Foundation Pit Adjacent to a Metro

2022-01-18 2422 0人评论

01. Project Overview

The Xinsheng Wentao Building project is located north of Binwen Branch Road and west of Xipu Road in Binjiang District, Hangzhou. The south side of this project is close to Exit B of Xipu Road Station on Metro Line 6 and the shield tunnel section. At the nearest point, the outer edge of the retaining structure is about 6.700 m from the auxiliary structure of the metro station exit and about 29.90 m from the shield tunnel section on the south side. Before excavation of the foundation pit, Line 6 was already in the trial operation stage but not yet in commercial operation. To the west of the foundation pit is Binpu Road, and the pit edge is about 6.408 m from the road edge; to the east is Xipu Road, and the pit edge is about 30.898 m from the land acquisition red line. To the north is a newly built road, and the pit edge is about 3.0 m from the land acquisition red line at the nearest point.

The foundation pit of this project is about 260.9 m long in the east-west direction and about 111.0 m wide in the north-south direction, forming a "rectangle". The pit perimeter is about 743.8 m, and the pit area is about 88,000 m². There are three basement levels overall. The bottom of the foundation pit cushion layer is excavated to a large-area depth of 12.600 m, and considering the pile cap cushion layer, the excavation depth is 13.100 m.

02 Retaining Design Scheme

The excavation depth of the foundation pit in this project is 13.000 m. The design scheme is mainly determined based on the surrounding environmental impact of the foundation pit and the stratum conditions:

1. On the south side near Hangzhou Metro Line 6, a divided-pit arrangement is adopted, divided into four small pits, K1, K2, K3, and K4, using a support system of diaphragm walls plus three levels of internal bracing (the first level is concrete bracing, and the lower two levels are prestressed steel section bracing with a servo system).

2. On the west, north, and east sides, namely the large pit K5, a support system of bored cast-in-place piles plus two levels of internal bracing (the first level is single-piece steel section bracing, and the second level is double-piece steel section bracing) is adopted.