Abstract: It has been gradually recognized that threshold hydraulic gradient of seepage exists in soft clay. However, nonlinear large-strain consolidation of soft clay with threshold gradient, which takes time-dependent load into account, has rarely been reported in the literature so far. By employing the excess pore water pressure as variable, and considering both threshold hydraulic gradient and characteristics of nonlinear compression and permeability, a model for large-strain consolidation is developed in Lagrangian coordinate system. On that basis, the corresponding finite difference solutions for this model are provided. Meanwhile, compared with the semi-analytical solutions of large-strain consolidation under Darcy's law, the numerical solutions for the proposed consolidation model are verified. Finally, the differences in the influence of threshold hydraulic gradient on consolidation behaviors of clay between large- and small-strain conditions are emphatically investigated. The results show that, no matter large- or small-strain condition is considered, both the dissipation rate of excess pore water pressure and the settlement of clay layer become smaller than that under condition of Darcy's law when considering the influence of threshold hydraulic gradient. The excess pore water pressure in clay with threshold hydraulic gradient is not completely dissipated under both large- and small-strain conditions, moreover, the residual value of excess pore water pressure under large-strain condition is smaller than that under small-strain condition, which leads to a larger settlement of clay layer under large-strain condition than that under small-strain condition. Both threshold hydraulic gradient and different deformation conditions have influences on the consolidation behavior, while the influence of threshold hydraulic gradient is more evident. Therefore, the threshold hydraulic gradient of seepage in soft clay cannot be ignored during the consolidation calculation of soft clay layer.

Key words: soft clay, threshold hydraulic gradient, large-strain consolidation, finite difference method, nonlinear consolidation