Abstract
Partial supporting piles removal from deep foundation pit may lead to large‐scale foundation pit collapse, resulting in severe consequences. Various studies have investigated the underpinning technology of cutting abutment piles by combining field monitoring and numerical simulation, but there are few studies on cutting supporting piles of foundation pit by the shallow excavation method. Taking an actual deep and large foundation pit as an example, the finite element method (FEM) was adopted to study the surface settlement and the changing trend of the force and displacement of the supporting pile caused by cutting piles during the shallow excavation of double tunnels. The FEM results were verified with the field monitoring data. The simulation results show that the surface settlement around the foundation pit mainly occurs at the pile cutting stage under different excavation sequences (0D, 1D, 2D), and the main distribution area is the one‐fold diameter area outside the double tunnel. After the supporting piles are partially cut, the bending moment and displacement of the lower part of the broken piles differ significantly due to different excavation sequences, but the bending moment and displacement of the upper part of the broken piles are basically similar. In the process of removing the supporting piles, the Earth pressure behind the piles is redistributed, and the load is mainly transferred to the adjacent supporting piles outside the tunnel within the radius of one time of the tunnel diameter. However, the load is not evenly transferred to the adjacent supporting piles. Some recommendations for the reinforcement scheme of the supporting structure during cutting supporting piles in deep foundation pit are also proposed. The research results can provide theoretical basis and practical guidance for the construction of similar projects in the future.
Highlights
Deep excavation engineering is widely applied in the construction of high-rise buildings, metro stations, and underground transportation centers
In order to study the mechanical effect of cutting supporting piles during shallow excavation, the trends of surface settlement, pile displacement, and supporting structure internal force were investigated. e numerical simulation sequence is the same as the actual construction process (Table 1) and focuses on the construction process of cutting piles by the shallow excavation method. e numerical model is shown in Figure 3. e moment at which the leftside supporting pile is cut is denoted as “MPL” and that of the right side is denoted as “MPR.” e moment of tunnel construction completion is denoted as “F” and the moment the piles are cut simultaneously is denoted as “MP.”
The characteristics of surface settlement and the mechanical effects of partially cutting supporting piles in a deep excavation structure were investigated using a series of finite element method (FEM) simulations under different working conditions. e model was validated by comparison to a high-quality case
Summary
Deep excavation engineering is widely applied in the construction of high-rise buildings, metro stations, and underground transportation centers. E effects of pile cutting such as load transfer, internal force, and deformation of the supporting structure are not clear. These factors can pose severe risks to the safety of the deep foundation pit. A 3D numerical analysis model of cutting supporting piles during the shallow-buried excavation of double tunnels under different excavation spacing conditions was established and combined with field monitoring data. As a typical engineering problem that will surely continue to be encountered in the future, the general trends of load transfer, internal force, and deformation of the supporting structure after partial piles removal have considerable reference value
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