Comprehensive multivariate joint distribution model for marine soft soil based on the vine copula

In this study, we propose a multivariate joint distribution model for marine soft soil using D-vine copula function. The model is based on detailed investigation data from a tunnel constructed in marine soft soil. The variation patterns of the mechanical and physical parameters of quaternary marine–land interaction sedimentary soft soil layers were analysed. First, a comprehensive database of marine soft soils was established on the basis of detailed field investigation data. The variability and correlations among the physical and mechanical performance indices of the soft soil were then analysed. Subsequently, optimal marginal functions for nine soil parameters were proposed on the basis of the fitting characteristics of the physical and mechanical performance parameters of the soft soil. Finally, 15 copula functions were used to establish a multivariate joint distribution model of the D-vine copula function for marine soft soil, and the effectiveness of the model was verified. This model offers flexibility for constructing multivariate joint distributions tailored to various characteristics of the correlation structure by leveraging several bivariate correlation structures. It can provide an effective method for accurately delineating the features of the correlation structure among multivariate geotechnical parameters and establishing a probabilistic transformation model for marine soft soil parameters.