Strict deformation control of foundation pit enclosure structures is critical in complex surrounding environments, as excessive deformation seriously affects the stability and safety of adjacent buildings and infrastructure. For tunnel-first and station-later (TFSL) metro foundation pit excavations involving shield segment removal, rational removal methods can effectively reduce the deformation of the foundation pit and ensure the safety of surrounding important buildings. No prior studies have reported the application of the sand-blowing and grouting backfill method for segment removal in TFSL foundation pits. A three-dimensional numerical model for a TFSL foundation pit in Kunming was developed using PLAXIS 3D finite element software. The numerical simulation results based on the hardening soil with small strain stiffness (HSS) and Mohr-Coulomb (M-C) models were compared with the field monitoring data. Results indicate that the proposed method for segment removal substantially reduces deformation in the enclosure structures, surrounding buildings, and ground. The critical deformation stages of the enclosure structures and surrounding buildings occur during soil excavation and segment removal within the shield tunnel range. Deformation results simulated through the HSS model closely match the monitoring data, while those from the M-C model show notable deviations or even contradictory trends, demonstrating the superior practicality of the HSS model for deformation analysis in deep foundation pits under complex conditions.