MUHAMMAD RIZWAN

Variation of small strain shear properties of loose sand induced by liquefaction

Hirofumi TOYOTA

Liquefaction significantly affects the mechanical behaviour of loose sandy soils, particularly at small strain levels that are critical for seismic ground response and estimation of small ground deformation during construction. This study investigates the variation of small-strain shear properties of loose sand considering liquefaction histories. A series of laboratory experiments were conducted using cyclic triaxial tests combined with local small strain (LSS) and bender element measurements on Toyoura sand specimens prepared at a relative density (Dr) of 40% at depositional angles of 0��, 45��, and 90��. The results were compared with data for Dr = 60% obtained from a previous study, which was used to discuss the range of application using previous and current achievements.

The results show that, before liquefaction, the initial shear modulus (G0) increases with increasing depositional angle, indicating anisotropic soil behaviour. However, after liquefaction, G? becomes independent of depositional angle, indicating that the liquefaction process largely changes the soil structure. In addition, the degradation of secant shear modulus (Gsec) at Dr = 40% is more pronounced than at Dr = 60%, highlighting the greater susceptibility of loose sand to stiffness reduction under cyclic loading.

To study the mechanism of soil liquefaction, the relationship between liquefaction resistance and small-strain shear properties was investigated. The results showed a strong correlation between liquefaction resistance (CRR) and shear modulus at very small strain levels (0.001% and 0.01%) for both Dr = 40% and Dr = 60%. This suggests that small-strain shear properties can provide a reliable indicator for assessing liquefaction resistance. However, Gsec at strain level greater than 0.01% showed the opposite trend with CRR.

Overall, the effects of liquefaction history on mechanical properties was able to well explain using variation of particle orientation measured by optical microscopy. These findings contribute to more accurate prediction of ground liquefaction under seismic loading.