Reply to the two discussions on my paper "An alternative mechanism of pile failure in liquefiable deposits during earthquakes"
This paper proposes an alternative mechanism of pile failure in liquefiable deposits during earthquakes. This failure mechanism, based on pile buckling, is formulated by back-analysing 14 case histories of pile foundation performance during earthquakes and verified using dynamic centrifuge tests. A new parameter, the slenderness ratio of a pile, is introduced to classify pile performance in liquefiable soils. This parameter fits very well both the reported case histories and the centrifuge test results.
A Reconsideration of the Safety of Piled Bridge Foundations in Liquefiable Soils
ABSTRACT The collapse of piled foundations in liquefiable soil has been observed in the majority of recent strong earthquakes. This paper critically reviews the current understanding of pile failure in liquefiable deposits, making reference to modern design codes such as JRA (1996), and taking the well-documented failure of the Showa Bridge in the 1964 Niigata earthquake as an example of what must be avoided. It is shown that the current understanding cannot explain some observations of pile failure. The current method of pile design under earthquake loading is based on a lateral loading mechanism where inertia and drag due to slope movement (lateral spreading) induce bending in the pile, and where axial load effects are ignored. It is demonstrated here, however, that axial loads can be a dominant factor in collapse due to seismic liquefaction, due to the progressive onset of pile buckling when lateral soil resistance is removed. Additional design considerations based on the avoidance of buckling effects are formulated after back analysing fifteen case histories of pile foundation performance during past earthquakes, and verified using dynamic centrifuge modelling. Some practical implications of the omission of axial loads from previous design verifications are highlighted.
On the use of the Hardening Soil Small Strain model in geotechnical practice
This article highlights the importance of using advanced constitutive soil models in numerical modelling as daily geotechnical practice. In this context, the Hardening Soil (HS) model is presented as the most advanced soil model implemented in the ZSoil finite element code. The article recalls the basic features of the HS model and it explains their role in numerical simulations. The role of pre-failure non-linear behaviour of soils is also discussed. An application of the HS model is illustrated on typical geotechnical problems such as retaining wall excavation, tunnel excavation and undrained loading followed by consolidation.