Liquefaction resistance of undisturbed and reconstituted samples of a natural coarse sand from undrained cyclic triaxial tests

The paper deals with an experimental study of the undrained cyclic behavior of a natural coarse sand and gravel deposit located in Gioia Tauro, a town situated on the continental side of the Messina Strait in Italy. The study was conducted through cyclic undrained triaxial tests carried out on both undisturbed and reconstituted samples. Undisturbed samples were recovered by an in situ freezing technique and the sample quality was carefully assessed. Reconstituted samples were prepared by using two different reconstitution methods, namely air pluviation (AP) and water sedimentation (WS), and tested under the same in situ initial relative density and effective overburden stress. Tests were carried out on both isotropically and anisotropically consolidated specimens. The results obtained from this study provide direct evidence that cyclic liquefaction resistance obtained from water sedimented samples closely approximates that exhibited by undisturbed samples in both isotropically and anisotropically consolidated tests. Conversely, AP leads to a marked underestimation. Since the investigated deposit is considered to have been formed by the marine water environment, these results can be regarded as proof that WS closely replicates the in situ fabric of the investigated deposit allowing the substitution of the expensive undisturbed samples with their reconstituted counterparts. Anisotropically consolidated specimens respectively exhibit "cyclic liquefaction" or "cyclic mobility" depending on whether or not they are loaded under the shear stress reversal mode.