ANISOTROPY AND ITS RELATION TO LIQUEFACTION RESISTANCE OF GRANULAR MATERIAL

ISAO ISHIBASHI and OMER F. CAPAR

ABSTRACT: This research establishes quantitative relationships between soil's anisotropy and liquefaction resistance for granular materials. Uniform medium density (D_r=50 %) sand specimens were prepared using three different sample preparation techniques (air pluviated (AP), moist tamped (MT), and moist vibrated (MV)) to create different initial soil fabrics. Undrained cyclic triaxial tests were then performed to determine the liquefaction resistance of each soil specimen. On the same specimens in the triaxial cell, vertical and horizontal compression wave velocities and vertical shear wave velocity (V_s) were measured using piezoelectric bender elements. Anisotropic (transversely isotropic) elastic constants of the soil specimens were determined from the elastic wave measurements and additional consolidation test data. With the aid of additional data from earlier discrete element model (DEM) simulations, anisotropic parameters, which influence the liquefaction resistance, were examined. It was found that when liquefaction resistance is divided by G₁₂/(E₁/E₂)³ , by G_average/(E₁/E₂)³, or by V_s^5.0 , liquefaction resistance curves converge to a unique curve regardless of the sample preparation techniques. Liquefaction Stress Ratio Reduction Factor (LSRRF) was introduced to estimate the reduction of liquefaction cyclic stress ratio of an anisotropic specimen from the isotropic specimen as simple functions of (E₁/E₂)^-5.0 or (V_s/V_s(iso.))^5.0.

Key words: anisotropy, discrete element model, elastic modulus, granular material, laboratory test, liquefaction, numerical simulation, piezoelectric sensor, wave velocity (IGC: D7)