The failure concept in Soil Mechanics revisited

摘要

When applied to porous materials characterised by a non- associate flow rule such as soils, the apparently self evident concept of failure becomes less neat. Although it is possible to define a convenient limit locus beyond which stress states are not feasible for a given material, unlimited strains may occur even for stress states within such locus, provided convenient loading conditions are imposed and controlling parameters appropriately chosen. It is shown that such type of failures can occur in the hardening regime, provided the flow rule is non-associate and the stiffness matrix is not positive-definite. Failures due to loss of load control in undrained tests or shear or compaction band occurrence are examples. The related concepts of hardening ad softening are discussed. It is shown that, contrary to primitive expectations, hardening may occur even with decreasing deviator stress, while softening may be associated to a load increment.