permanent behaviour

Permanent deformation in UGMs is mainly related to resilient stresses or strains and number of load cycles. The effects of these two factors are often separated and the models for predicting permanent deformations can assume the form of:
                                                                                                               (1)
Amongst the numerous models that are available in the literature, Hornych (2004) shows that the Gidel model is particularly suitable to describe the variation of permanent deformations with stress level:
                                                                                              (2)
The link between permanent deformation and number of load cycles can instead be expressed by the simple Sweere model:
                                                                                                                                                (3)
or by the slightly more elaborated Hornych model:
                                                                                                                          (4)
All these models are derived empirically by fitting curves to laboratory data and do not take into account the effect that moisture content has on the permanent behaviour of the granular material. In theory, a different set of fitting parameters would need to be calculated for each value of moisture content considered. The ME-PDG, instead, uses a modified version of the Tseng and Lytton model that relates permanent strains to resilient strains, number of cycles and moisture content:
                                                                                                                      (5)
where β, ρ and ε₀/ε_r are functions of water content.

Posted in: deformation, granular, materials, model