Constitutive Behavior of Geosynthetic Interfaces

Abstract

New displacement-softening and work-softening models were developed to describe the sliding of geosynthetic interfaces, such as those in landfill liners. The displacement-softening formulation is based on the assumption that strength reduction at the interface can be related to nonrecoverable (plastic) shear displacement. The model uses three relationships: (1) the peak strength envelope; (2) the residual strength envelope; and (3) the residual factor versus displacement ratio relationship, which is a nondimensional expression of the rate at which displacement-softening occurs. The displacement-softening model is accurate for shearing when the normal stress stays constant. When normal stress increases during shearing, the displacement-softening formulation overpredicts damage to geosynthetic interfaces. The work-softening model was developed to compute interface softening during conditions of increasing normal stress. This formulation is based on the assumption that the postpeak reduction in shear strength can be attributed to plastic shear work rather than plastic shear displacement. By calculating an equivalent plastic shear displacement for a given amount of plastic shear work, the work-softening model can be formulated using the same basic relationships as the displacement-softening model. The work-softening model significantly outperformed the displacement-softening model when simulating laboratory tests under conditions of increasing normal stress.