Abstract
Based on a long-term comprehensive instrumentation program, the performance of an excavation pit constructed by the top-down method in downtown Kunming was extensively examined. The measured excavation responses included the deflections of diaphragm wall, vertical column movement, slab axial force, building settlement caused by ground deformation, and the influence of pit excavation on the adjacent subway tunnel. This paper analyses the monitoring data of the existing construction stage. Based on the analyses on the data of field and numerical simulation, the following major findings were obtained: (1) the relationship between the measured maximum wall deflection, δ h m , and excavation depth, H , in this study is δ h m = 0.06 % H ∼ 0.27 % H , which is quite different compared with the relationship of soft-soil pit δ h m = 0.02 % H ∼ 1.2 % H , but closer to the normalized curve of rock-socketed pile δ h m = 0.01 % H ∼ 0.45 % H and rock-socketed diaphragm wall δ h m = 0.031 % H ∼ 0.129 % H . (2) The relationship between the maximum settlement of column ( δ p ) and excavation depth ( H ) is δ p = − 0.09 % ∼ 0.04 % H . The maximum distortion between the diaphragm wall and the column is less than 1/500 of the limit range proposed by Bjerrum. (3) The impact range caused by excavation is about 3.8 times the maximum excavation depth. The ground settlement around the foundation pit is groove type, and the maximum settlement point is located at 2.7 times the maximum excavation depth. (4) The excavation of the foundation pit leads to the maximum vertical settlement of 2 mm and maximum horizontal displacement of 5.2 mm in the subway tunnel; the maximum change of axial force and bending moment are 8.8 kN (the vertical direction) and 6.4 kN·m/m (the horizontal direction), respectively.
Highlights
Chang et al [14] analyzed the field monitoring data and found that a subway tunnel will reduce the ground displacement caused by pit excavation. e longitudinal direction of the tunnel has a great influence on the deformation bearing value of the tunnel
It can be found that theoretical method and numerical method are commonly used research methods, but because of the complexity of foundation pit construction boundary, it is difficult to solve the influence of foundation pit excavation on surrounding environment by theoretical method, and numerical method provides a powerful tool for solving this problem [24]
It started with the construction of a 1 m thick diaphragm wall. e diaphragm wall was toed through the silty clay layers into the underlying moderately weathered limestone to provide lateral stability and effectively cut off groundwater. e load-bearing elements consisted of augercast-in-place (ACIP) piles, and the diameter is 1 m, which penetrated the strongly weathered limestone layers
Summary
For some reasons, after the completion of B2 slab (10.8 m), some areas were excavated to 12 m, and the foundation pit stopped construction. It started with the construction of a 1 m thick diaphragm wall. A long-term comprehensive instrumentation program was conducted in situ to monitor the deep excavation performance for securing the safety of this project. E distance between monitoring points is 20 m, and the distance between monitoring points is reduced to 10 m in the section with large deformation of foundation pit supporting structure To ensure the safety of the subway tunnel, deformation observation points are set on the sidewall and vault of the subway tunnel and monitored by the level instrument. e distance between monitoring points is 20 m, and the distance between monitoring points is reduced to 10 m in the section with large deformation of foundation pit supporting structure
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