Further insight into the behaviour of Pleistocene Osaka clays at KIA Phase 1 island

Abstract

The behaviour of the Pleistocene Osaka clays at Kansai International Airport Phase 1 island is investigated by FEM analyses using an elasto-viscoplastic constitutive model which replicates the destruction processes occurring in the microstructure of the clay. Excellent predictions are obtained by 2D analyses carried out using the actual soil profile and the characteristic values of soil parameters, confirming the validity of the methods proposed for characterizing and modelling structured clays. Unlike 1D analyses, where partially effective drainage layers occur, 2D analyses do not require arbitrary pre-definition of the model drainage scenario and of the ‘equivalent’ permeability of interlayered clays to account for macrostructure. In these conditions, 1D analyses must be validated with reference to 2D or 3D prototype analyses and/or well documented experience of comparable work. Once thus validated, 1D analyses are used to investigate the relative merits of possible measures (relief wells, preloading, lightweight fill) aimed at reducing in-service settlement. For future reclamation works at sites where structured clays extend to great depth, filling with lightweight material shows the greatest promise, but it is unlikely to remove the need for designing the superstructure to accommodate the inevitable settlement, which requires accurate prediction.