The cyclic threshold shear strains in very dense clean sand

Abstract

Shear strain in soil is one of the most important factors controlling the response of soil layers under earthquake. Therefore, recognition of changes in soil behaviour under different strain amplitudes is necessary. Based on the published experimental data, alternative cyclic strain regime divisions are proposed. The cyclic strain thresholds that represent the change in cyclic behaviour and properties of soil are used to divide these different cyclic strain regimes. The criteria taken into account to obtain these regimes include stress–strain behaviour, pore-water pressure generation, volume change, stiffness degradation, post-cyclic strength and micro-scale processes. In this study, the cyclic threshold shear strains for pore-water pressure generation, stiffness degradation and post-cyclic strength are investigated in very dense clean sand. It is specified that the cyclic threshold shear strain for pore-water pressure generation in very dense sand is higher compared to those relating to loose and relatively dense sand which is referred to in the literature. Moreover, two methods referred to in the literature are compared to calculate the threshold strain of stiffness degradation. Also, it was determined that when pre-cyclic shearing is more than a specified amplitude, the positive effect of pre-loading due to increasing relative density and the shear strain history can be eliminated or even can be inverted.

Keywords:

• undrained cyclic loading
• dense sand
• threshold strain
• post-cyclic strength
• stiffness degradation
• hollow torsional