The deformation mechanism of the foundation pit is not consistent with the real in-situ deformation in traditional method for stability analysis. The surface settlement curve caused by foundation pit excavation in soft soil area enables the establishment of the admissible velocity field and deformation mechanism for basal stability problems in excavations. The soil inside the deformation mechanism acts as a continuous deformation body without apparent failure surface at the boundary. A new method for the stability analysis of foundation pit is developed based on upper bound method. The deformation mechanism adopted in the method is more suitable for the foundation pit deformation

considering the influence of the depth of supporting structure on the uplift deformation of foundation pit. The upper bound method based on Terzaghi mechanism and Prandtl mechanism is compared with the multi-block upper bound method in engineering examples to verify its rationality and applicability.