1D elastic viscoplastic consolidation analysis of bi-layered soft ground under time-dependent drainage boundary and ramp load

The elastic viscoplastic properties are non-negligible factors of clays that cause the deviation between the theoretical and the measured values, which were rarely incorporated in layered consolidation problems. Thus, this paper extended a generalized bi-layered one-dimensional (1D) consolidation model for soft ground under ramp load, simultaneously incorporating elastic viscoplastic deformation, non-Darcy flow (NDF), and time-dependent drainage boundary (TDB) condition. The finite volume technique was employed to numerically solve the control equation. Then, the proposed method solutions were verified by comparing with degenerated cases, including oedometer experimental results, analytical and semi-analytical solutions with different boundary conditions. Furthermore, parametric studies were conducted on the bi-layered clay creep consolidation characteristics by investigating the effect of the loading rate, interface and flow parameters, and the relative soil layer properties. The results demonstrate that the entire dissipation rate of the excess pore-water pressure (EPWP) and settlement rate in the bi-layered ground become faster as the soil thickness with high permeability or low compressibility increases. When considering the viscosity of soft clay, the EPWP exceeding the overlying construction load value can occur in poorly drained locations. Neglecting loading rate, time-dependent drainage boundary (TDB), and NDF can result in a significant overestimation of consolidation and settlement proceedings.