Normalisation of cyclic undrained triaxial and simple shear strength of carbonate sand to monotonic shear strength

Silica sands have been researched extensively, for both static and dynamic loading conditions, and their behaviour is comparatively understood; in contrast, less attention has so far been paid to the behaviour of carbonate sands. The paper presents results from both cyclic and monotonic undrained simple shear (SS) and triaxial (TX) tests carried out on a calcareous bioclastic sand from a marine French deposit (Quiou sand). Reconstituted specimens were formed by water sedimentation method, which is able to reproduce more properly the fabric of natural deposits of marine origin (Ghionna & Porcino 2006). Use is made of a unified framework in which undrained monotonic and cyclic response can be comparatively analysed. In particular, based on the results of SS and triaxial tests, a close relationship between the cyclic undrained shear strength and the normalised monotonic strength corresponding to the phase transformation state, is verified. It is found that such a relationship is practically unique for a given sand, irrespective of initial void ratio and vertical effective stress. Finally, it was disclosed that the correction factors proposed in literature for comparing cyclic liquefaction resistance curves from simple shear vs. triaxial testing apparatus can also be applied to the data of carbonate sands.