Effects of Partial Supporting Pile Removal from Deep Foundation Pits by Shallow Excavation Method in Loess Areas

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.

Study on Design and Deformation Law of Pile-Anchor Support System in Deep Foundation Pit

“…The literature [22][23][24][25][26][27][28] analyzed the layout principle of monitoring points in the monitoring process of deep foundation pit horizontal displacement, settlement, anchor prestress, soil nail stress, slope water, and soil pressure, through specific engineering examples and field tests, monitoring schemes, data acquisition, and processing and analysis, and summarized the stress and deformation laws. The literature [11,[29][30][31][32][33][34][35] applied the theory to the monitoring data processing and inversion analysis to obtain the support structure and stratum stress, compared them with the design results to evaluate the rationality of the design, and discussed the corresponding improvement methods from a theoretical perspective. The literature [36][37][38][39] proposed a three-dimensional space effect of the foundation pit retaining structure deformation by monitoring a deep foundation pit in soft soil.…”