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

Abstract

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 postcyclic 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.

Liquefaction and post-liquefaction of granular material under multi-directional cyclic loading

“…13a, the specimens with liquefaction history shift shear behaviour from strain-softening to strain-hardening. Similar conclusions have been reported in the previous studies (Porcino et al, 2009;Bastidas et al, 2017) that were conducted through post-liquefaction undrained cyclic tests of sand and by using uni-directional simple shear devices.…”

Postcyclic behavior of low-plasticity silt with limited excess pore pressures

“…Porcino et al [10] conducted a series of cyclic shear tests on uncemented carbonate sands (Quiou sand) using the modified NGI cyclic simple shear device. Reconsolidation was allowed after cyclic loading.…”

The cyclic threshold shear strains in very dense clean sand

“…The strength drastically decreases for γ bigger than 3 and 4.5%. This represents the negative effect of a cyclic pre-loading which is larger than the threshold strain (Porcino, Marciano, & Ghionna, 2009). The value of threshold pre-strain for this sand in very dense condition is between 1.0 and 2.0%.…”