Elastic viscoplastic consolidation modelling and interpretation of pore-water pressure responses in clay underneath Tarsiut Island

It has been reported that the excess pore-water pressure in clay underneath Tarsiut caisson retained island increased for many months following completion of construction (with vertical load unchanged). It was thought that this increase might be caused by the creep behaviour of the soft clay. However, the phenomenon of excess pore-water pressure increase under constant loading has not been simulated successfully at the Tarsiut Island site. In this paper, a newly developed elastic viscoplastic (EVP) model is implemented in a finite element (FE) program for consolidation analysis. This FE program is used to model the consolidation behaviour of the clay under Tarsiut Island loading. The phenomenon of pore-water pressure increase with time following completion of construction of the island has been successfully simulated using the FE program with the new EVP model. The mechanism of the pore-water pressure increase is explained. It is found that the creep compression nature of the clay is the main internal factor causing the increase. However, the volumetric strain (change) produced due to the dissipation of excess pore-water pressure is the external factor which combines with the internal factor to cause decreasing effective stress and increasing pore-water pressure.