Liquefaction Susceptibility of Saturated Coral Sand Subjected to Various Patterns of Principal Stress Rotation

The influences of consolidation conditions and rotation patterns of principal stress on the liquefaction susceptibility of saturated coral sand have emerged as an interesting problem in recent years. This paper presents results from a comprehensive experimental study comprising undrained monotonic shear tests and undrained cyclic shear tests subjected to various patterns of principal stress rotation. A remarkable finding is that a virtually unique correlation exists between a generalized shear strain amplitude ${\gamma }_{ga}$ and the excess pore water pressure ratio $r_u$ irrespective of consolidation conditions and cyclic loading patterns. A simple formulation is then proposed to relate ${\gamma }_{ga}$ and $r_u$. Another significant finding is that the liquefaction susceptibility of coral sand and the correlation between the conventional cyclic stress ratio (CSR) and the number of cycles to failure $N_f$ (corresponding to ${\gamma }_{ga}=2.5\%$) are strongly affected by the couplings of consolidation conditions and cyclic loading patterns. By introducing a generalized unit cyclic stress ratio ($US{R}_g$) as a new proxy for liquefaction resistance, a strong correlation is found between $US{R}_g$ and $N_f$ for all data sets from the experiments. An explicit relationship is then proposed for practical application. The wide applicability of this relationship is well demonstrated using the literature data for various undrained cyclic laboratory tests and different sands.