Abstract: The unsaturated intact loess has obvious structural characteristics which significantly affect its mechanical behaviors. However, introducing structural characteristics into multi-field coupled analysis of collapse deformation for unsaturated loess foundation has not been widely reported, and further research is urgently needed in this field. Based on the established elastoplastic damage constitutive model for unsaturated intact loess combining water – gas migration law of unsaturated loess, a new elastoplastic damage seepage-consolidation coupled model is presented in this paper, which considers the influence of structural damage. The concrete expressions of the governing equations of the new coupled model in the two-dimensional coordinates are derived, and the governing equations are discretized in time domain and space domain by Galerkin method, respectively. At the same time, the concrete expressions of each element of the modulus matrix are obtained, and a multi-field coupling finite element program named after ULEDSC is compiled. Large field immersion test of loess foundation is simulated by this new program (taking in-situ soaking test of the self weight collapsible loess site in Heping town, Lanzhou city, Gansu province as an example). The pore pressure, displacement and damage fields during wetting and subsequent drying processes are obtained in this paper, which reveals the multi- field coupling response of self weight collapsible loess foundation because of the action of water and self-weight of loess. The research results in this paper can give scientific basis for the project design of loess area, and the new compiled finite element program is a powerful tool to solve the problem of loess collapsibility.

Key words: unsaturated loess, structural characteristics, elastoplastic damage, collapsible deformation, seepage-consolidation coupled model