Research on Surface Settlement Characteristics of an Underwater Shield Tunnel Based on Conditional Random Field Theory

The construction of underwater shield tunnels is highly vulnerable to water inrush, particularly due to excessive surface settlement in complex geotechnical conditions. Therefore, accurately predicting surface settlement during construction is essential for ensuring safety. To address this, an analysis method for surface settlement deformation of underwater shield tunnel based on conditional random field (CRF) is proposed in this study. First, using the random field (RF) theory based on the Gaussian autocorrelation function and Karhunen–Loève series expansion method, the ordinary Kriging method is introduced to establish the CRF theory. Subsequently, using borehole data, a CRF model of rocks hydraulic parameters is constructed and compared with model based on the existing RF theory. Finally, considering the hydromechanical coupling, a numerical model of the finite difference method is established, and the settlement and deformation characteristics of underwater shield tunnels based on the CRF theory and the RF theory are compared and analyzed. The results show that the CRF model can accurately characterize the spatial variability of geotechnical parameters and reach convergence faster than the RF model with better stability. In addition, compared with the RF model, the settlement curve based on the CRF model is more concentrated and the discrete range is significantly reduced, and the settlement range is reduced by 20%–30%, indicating that the settlement prediction method for underwater shield tunnel based on the CRF model has obvious advantages. The analysis method offers a more reliable theoretical basis and technical support for surface settlement approach during underwater shield tunnel construction, contributing to enhanced safety and efficiency in engineering construction.