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Single Piles in Liquefiable Ground : Seismic Response and Numerical Analysis Methods Abstract The seismic response of piles in liquefiable ground is an important and challenging topic in the field of geotechnical earthquake engineering. Through a combination of case analysis, centrifuge shaking table experiments and numerical simulations, the seismic response patterns of single piles in liquefiable ground are revealed, and the axial pile force and settlement during post-earthquake reconsolidation is studied. A complete set of numerical method for the analysis of single piles in liquefiable soils is established, consisting of constitutive formulations, numerical algorithms and modelling techniques. The main achievements are as follows: 1. A three-dimensional unified plasticity model for large post-liquefaction shear deformation of sand is formulated and implemented for finite element analysis, based on which a three-dimensional dynamic finite element analysis method for piles in liquefiable ground is developed. The constitutive model is able to achieve a unified description of the behaviour of sand at different states under monotonic and cyclic loading during both pre- and post-liquefaction regimes. Appropriate stress integration algorithm, three-dimensional stress projection algorithm and parallel computation techniques are applied in the OpenSees implementation of the model. The potential of the model and its numerical implementation are explored via simulations of classical element and centrifuge experiments. The finite element analysis method is validated against centrifuge shaking table experiments. 2. Methods for the analysis of consolidation and reconsolidation-induced pile axial force and settlement with a consideration for consolidation process are proposed. A beam on nonlinear Winkler foundation (BNWF) solution and a modified neutral plane solution are developed and validated against centrifuge experiments for piles in consolidating and reconsolidating ground. 3. The seismic response of single piles in liquefiable ground is studied, including basic force-resistance mode, kinematic and inertial interaction coupling mechanism and major influence factors. The roles of kinematic and inertial effects could differ due to the difference in rotational constraint at the pile head. Moment caused by kinematic and inertial interaction is opposite for single piles with pile cap, while being of the same direction for single piles without pile cap. The total moment caused by dynamic interaction is affected by both the amplitude and the phasing of the two types of interactions. The dominating forces for piles with and without caps are kinematic and inertial forces, respectively. Pile residual moment increases with increasing lateral spreading in sloping ground. The existence of a non-liquefiable layer over the underlying liquefiable layer may cause the maximum moment to occur at the layer interface. 4. The axial forces and settlement of piles during post-earthquake reconsolidation were analysed. The maximum pile axial force caused by post-earthquake induced negative friction is irrelevant to the reconsolidation process, and is only determined by the final state of the ground. However, pile settlement is dependent on the soil settlement at the neutral plane during reconsolidation, while the neutral plane position changes during the reconsolidation process. Keywords : Liquefaction Pile foundation Constitutive model Seismic response pattern Numerical analysis method منبع @Civilbest,_Rui_Wang_auth__Singl.pdf

Application of the Hardening Soil model in deep excavation analysis The Mohr–Coulomb model (MC) is commonly used in deep excavation analysis for its simplicity. However, it has shortcomings that may produce unrealistic soil behaviour. The Hardening Soil model (HS) is an advanced soil model that is able to generate more realistic soil response in terms of non-linearity, stress dependency and inelasticity. This article highlights some of the shortcomings of the MC model and presents a simplified approach to determine the HS parameters for drained and undrained analysis of deep excavations. Three case studies were back-analysed to validate the application of the HS model for practical excavation analysis. The HS model suffers the same problems as the MC model in using effective stress parameters c0 and f0 to determine the undrained shear strength. Keywords: Hardening Soil model; Mohr-Coulomb soil model; excavation; constitutive model; nonlinearity; backanalysis منبع hs&mc.pdf