Monitoring and numerical simulation analysis of a pit-in-pit excavation of the first branch line of Lanzhou Metro

Based on the pit excavation project in a station of Lanzhou Metro, the horizontal displacement of bored piles, the ground settlement around the foundation pit, and the supporting axial force in the foundation pit were tested on site. The changing rules and influencing factors of horizontal displacement of external and internal bracing piles during foundation pit construction are analyzed. Comparing the measured results with the numerical simulation results, the results show that the finite element calculation results can meet the engineering needs, the pile-support system can effectively control the deformation of the foundation pit, and the bottom of the outer pit has an obvious uplift. The numerical simulation is used to study the influence of different working conditions on the deformation of the foundation pit. The results show that the inner support of the foundation pit can control soil deformation more effectively than the outer support of the foundation pit. The study can provide a reference for the construction of such foundation pit in Lanzhou in the future.