Subways constructed in coastal cities along rivers commonly traverse water-rich soft soil layer,necessitating careful consideration in the design and construction of foundation pits for subway stations.The optimization of foundation pit parameters is closely related to the safety of engineering construction.Based on the foundation pit project of a typical water-soft land and the framework of random field theory,this study integrates a comprehensive coupling of non-invasive random analysis,the finite difference method and a Hermite polynomial response surface agent model,to establish a non-invasive finite difference model for foundation pits in water-rich soft soil.The study analyzes the deformation patterns during construction and assesses the failure probability of deep foundation pits situated within water-rich soft soil layers.The reliability of excavation deformation of deep foundation pit is calculated using the non-invasive random finite difference method,and the design parameters and construction parameters of foundation pit are optimized.The results show that the third-order PCE method is close to the Monte Carlo method in calculation accuracy but significantly more efficient.Changes in the vertical position of the fourth steel support have a great influence on the foundation pit deformation,and the failure probability can be clearly reduced by moving the position down 0.5 m-1 m from its original position.The stiffness of the underground continuous wall has a considerable influence on the foundation pit.When the stiffness increases from 1.0E0 to 1.1E0,the failure probability of surface settlement decreases by 27.11％.The depth of the underground continuous wall below 35 m has a relatively minor effect on the deformation of the foundation pit,and a depth of 35 m-37 m is appropriate.The dewatering depth of the foundation pit is negatively correlated with the failure probability of the deformation.When the dewatering surface is 1.5 m below the excavation surface,the reliability of the foundation pit is significantly enhanced.The research results provide a new,simple,quick and reliable method for selecting design and construction parameters of water-rich soft soil foundation pit.
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