Influence of cyclic pre-shearing on undrained behaviour of carbonate sand in simple shear tests

The paper will offer insights regarding the effects of cyclic prestrain history on the undrained behaviour of an uncemented carbonate sand (Quiou sand) through a modified NGI simple shear (SS) apparatus. Tests were carried out on specimens reconstituted at two void ratios (loose and dense) by using the water sedimentation method. The influence of cyclic undrained pre-shearing was investigated by applying both small and large limiting shear strains; after reconsolidation, the specimens were again subjected to the same cyclic phase as before, until the sample liquefied. The pattern of post-cyclic behaviour of the tested sand showed the relevant role assumed by the phase transformation line obtained from monotonic tests on virgin specimens. For both loose and dense specimens a threshold value of cyclically induced pre-shear strain was found at which the positive effect of previous cyclic loading history on liquefaction resistance disappears or starts to reverse. A normalising criterion, capable of providing a unified description of the pore-pressure build-up curves for different pre-shearing histories, was verified. Finally, a direct comparison between the tested sand and a silica sand with similar grain size features was also presented in order to ascertain the influence of particle crushing on the post-cyclic liquefaction behaviour.