Deformation and pore-water pressure responses of elastic viscoplastic soil

The deformation and pore-water pressure responses of clayey soils are of great interest to civil engineers. In this paper, displacements and pore-water pressures of a clay subjected to the loading of a strip footing are simulated using a fully coupled finite-element (FE) consolidation method incorporated with a newly developed 3D elastic viscoplastic (EVP) model for the clay. A brief introduction to the 3D EVP model and its implementation in the FE analysis is presented. The 3D EVP model can describe the time-dependent stress-strain behaviour of clayey soils, including volumetric creep. The main objective of this paper is to examine how the viscosity (or creep parameter ψ/V) of the clay affects the deformation and pore-water pressure responses of the clay. For this, the value of the creep parameter ψ/V is varied in the FE analysis. When viscous nature is taken into account, the pore-water pressure in the soil is higher than that without consideration of the viscous nature. The phenomenon of pore-water pressure increase due to creep is studied in this paper. It is found that larger creep parameter ψ/V results in higher pore-water pressure and larger deformation in the soil. The difference of the pore-water pressure due to the Mandel-Cryer effects and the creep is investigated using the FE model and discussed in this paper. In addition, a few other parameters (Poisson's ratio v, permeability k, clay layer thickness h, and thickness h to a half footing width a ratio h/a) are also varied to investigate their influence on deformation and pore-water pressure of the soil with creep. It is found that, the lower the permeability of soil, the higher is the pore-water pressure and the larger is the local deformation. The thickness of the soil layer also has a great influence on the pore-water pressure induced by the viscous effect. All these increased pore-water pressures result from a balance of the pore-water pressures induced by creep (and the Mandel-Cryer effects or both) and dissipated because of drainage.