Cyclic Threshold Shear Strains in Soils

Abstract

Based on a synthesis of published laboratory data, two types of cyclic threshold shear strain are examined and their approximate magnitudes identified for different types of soils. They are the linear cyclic threshold shear strain, γtl and the volumetric cyclic threshold shear strain, γtv, with γtv>γtl. These strains represent boundaries between fundamentally different categories of cyclic soil behavior. For cyclic strains below γtl, soil behaves essentially as a linearly elastic material. Between γtl and γtv, soil becomes markedly nonlinear but remains largely elastic because permanent changes of its microstructure still do not occur or are negligible. Above γtv, soil becomes increasingly nonlinear and inelastic, with significant permanent microstructural changes taking place under cyclic loading. That is, γtv, = the threshold separating cyclic strains that cause or do not cause significant permanent changes of soil microstructure. In practical terms, these microstructural changes are manifested in resid...