Dissipated energy in undrained cyclic triaxial tests

Energy-based methods are an emerging tool for the evaluation of liquefaction potential. These methods relate excess pore water pressure build-up to seismic energy dissipated per unit volume. Further development of these methods require their validation through laboratory testing. In this paper, a comprehensive study of energy dissipated during cyclic triaxial tests is undertaken. Results of undrained cyclic triaxial tests performed on air-pluviated samples of Hostun sand prepared with different initial densities and subjected to several confining pressures and loading amplitudes are presented. The energy dissipated per unit volume is estimated from the experimental results and correlated to the generated excess pore water pressure. The correlation between those quantities appear to be independent of the initial relative density of the sample, isotropic consolidation pressure and cyclic stress ratio used in the tests. Moreover, the relationship between observed doubleamplitude axial strain and the energy dissipated per unit volume is examined. It is found that this relationship is greatly dependent on the relative density of the sample

Critical state-based interpretation of the monotonic behaviour of Hostun sand

A series of bender element tests and drained and undrained monotonic triaxial compression and extension tests were performed on air-pluviated samples of Hostun sand. Samples were prepared to different initial void ratios, consolidated under various isotropic and anisotropic stress states, and sheared using different stress paths and a wide range of deformations to characterize the sand’s stress-strain response. The results suggest that the sand’s small-strain behavior essentially depends on the current void ratio and mean effective stress. Within the medium to large strain range, a state-parameter approach in conjunction with the critical-state framework can successfully predict the distinctive states of the sand’s monotonic response, namely the phase-transformation, peak-stress-ratio, and critical states. Furthermore, the data are used to examine a stress-dilatancy relationship often incorporated in constitutive models. The characterization presented herein aims at assisting the efficient calibration of numerical models and provides insight into this sand’s behavior, thus supporting the interpretation of results of physical modeling involving this sand. This paper highlights the importance of characterizing sand’s behavior over the full strain range and shows that accurate predictions of the critical state and small-strain stiffness are crucial to assess other aspects of the sand’s behavior

Effects of earthquake-induced liquefaction: Integrated research tools towards optimum reduction of society vulnerability

Earthquake-induced liquefaction is widely recognised as a serious hazard threatening modern societies. Indeed, even if the death toll is usually smaller than with other seismic phenomena, such as tsunamis, the economic and social distress and the extent of post-earthquake recovery caused by liquefaction are often more severe. This paper describes the research carried out at the University of Coimbra, Portugal, with its international partners, focusing on the assessment and mitigation of earthquake-induced liquefaction hazards at different levels and using different tools to reduce more effectively society's vulnerability to this phenomenon. Element testing has been combined with centrifuge modelling to assess the basic soil behaviour and the actual mechanisms governing field performance of geotechnical structures. Numerical modelling is used to extend experimental findings and to predict more accurately liquefaction effects, so that the principles of performance-based design can be used in current design practice. New energy-based design approaches and innovative planning tools for transportation infrastructures considering liquefaction hazards at a macro scale have been developed, allowing for better consideration of liquefaction effects in informed decision-making