No abstract

Inherent anisotropy, resulted from sediment process, is an important aspect when considering the behavior of sandy soils. Also, accurate initial shear modulus G0 at very small strain is an essential parameter in many seismic designs and analyses of underground structures. In this research, the influences of inherent anisotropy on G0 were investigated by conducting a series of triaxial tests employed both local small strain (LSS) measurement technique and bender element (BE) method. Specimens were prepared using air pluviation method in an inclined container at different angles to create the inherent anisotropy induced by orientation of sand particles. The experimental results obtained on both saturated and unsaturated sands indicate that G0 was affected by depositional angle of the specimen. Moreover, those results showed greater G0 on unsaturated sand than that on saturated sand because of the application of matric suction.

Because of water drainage, liquefied sand becomes denser after liquefaction. Therefore, such sand is not expected to liquefy again. However, repeated ground liquefaction has been reported from several earthquake events. We have considered some reasons for frequent reliquefaction: (1) the upper ground remains in a loose condition after liquefaction and (2) increased pore water pressure remains during subsequent earthquake events. This study investigated reliquefaction mechanisms using triaxial tests with bender elements (BE) and local small strain measurements (LSS) to explore other reasons for reliquefaction. The experimentally obtained results demonstrate that initial shear modulus G0 is insensitive to specimens with shear and liquefaction histories, although the liquefaction strength varies considerably according to the stress and liquefaction histories. The LSS test results indicate that the elastic strain region of sand shrinks according to the liquefaction history while maintaining almost unchanged G0. Furthermore, the sand particle orientation was evaluated from 2D images obtained using optical digital microscopy.