This paper revisits a famous phenomenon sometimes observed in granular soils: liquefaction. Liquefaction occurs when all stress components vanish. According to the loading conditions, and the initial void ratio of the soil specimen, it can be shown that a convenient stress quantity passes through a peak, and then decreases. It is usually thought that the deviatoric stress peak also corresponds to a failure state, since a sudden collapse of the specimen is expected from this point according to the loading control adopted. After a brief review of the theoretical background describing the occurrence of such phenomena (liquefaction and failure), the results of laboratory tests run along a triaxial proportional strain loading path are presented. Then, the main conclusions drawn are discussed and confirmed from numerical tests using a discrete element method. In both approaches, it is shown that the choice of the stress response variable is fundamental, in order to properly detect such a failure.

Keywords: proportional strain loading path, second order work, failure, liquefaction, limit state, experimental tests, discrete element method

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