Fully coupled numerical methods and a simple method for consolidation analysis of viscous clayey soils

In this paper, the authors firstly discuss the issues of large settlements of foundations or artificial islands on soft soil grounds, including the cases of the Tower of Pisa, Japan Kansai Airport Reclamations, and Hong Kong reclamations. Most of such large settlements can be attributed to the viscous behaviour (creep) of clayey soil skeleton. The mechanism of creep is briefly explained. The paper then presents Hypothesis A and Hypothesis B methods for calculating consolidation settlements of clayey soils, with the history and equations of the two hypotheses, explaining the inherent logical mistakes of Hypothesis A method. Two different methods for consolidation analysis of clayey soils are described, including the fully coupled numerical method with different Elastic Visco-Plastic (EVP) model, and a simplified Hypothesis B method, namely simple method, for one-layer and multi-layers of clayey soils. Steps of how to derive this simple method are presented. Two examples of using this simple method by hand calculations or spreadsheet calculations are explained. Verifications of the simple method by comparing with lab data and values from fully coupled numerical methods are presented, including a general simple method for multiple layers and vertical drains with analytical consolidation solutions by the spectral method (Indraratna and Walker, 2009). The fully coupled numerical methods and a simple method presented in this talk have been adopted in the 5th edition of “Canadian Foundation Engineering Manual” (CGS, 2023).