Liquefaction flow characteristics of saturated coral sand subjected to various patterns of cyclic loading

The accumulation of the excess pore water pressure of saturated sand under various cyclic loadings is the cause of soil liquefaction, and it is a relatively new research idea to treat the liquefiable sand as a fluid. A comprehensive experimental investigation of the liquefaction flow characteristics is performed for the saturated coral sand subjected to the jump of 90° and the continuous rotation of the principal stresses with cyclic loading frequency (f) at isotropic consolidations. The test results show that the relationship between the normalized apparent viscosity (η/η₀) and the excess pore water pressure ratio (r_u) is significantly affected by the cyclic stress paths, the degradation of η/η₀ with r_u is a progressive process, and a positive exponential correlation exists between the average flow coefficient ($\bar \kappa$) and r_u. The correlations between η/η₀ and r_u and between $\bar \kappa$and r_u seem to be independent on the cyclic stress ratio (CSR = 0.25~0.40) and f (= 0.1~1 Hz). Another significant finding is that the apparent viscosity gradient and the average flow coefficient gradient both increase first and then decrease with the increase of r_u regardless of the jump of 90° and the continuous rotation of the principal stresses, and r_u approximately equal to 0.9 at the reversal point can be regarded as the threshold value of the excess pore water pressure ratio (r_uth) at the phase transformation state from the solid state to the liquid one, by denoting the corresponding $\bar \kappa$ as ${\bar \kappa _{{\text{th}}}}$. The data points of $\bar \kappa /{\bar \kappa _{{\text{th}}}}$-r_u for all testing conditions are distributed in a narrow band, and a virtually positive exponential relationship exists between $\bar \kappa /{\bar \kappa _{{\text{th}}}}$ and r_u.