Deformation characteristics of sand with liquefaction history considering sand particle orientation

It has been widely reported that reliquefaction engenders under smaller seismic events than previous liquefaction. Once a sand undergoes liquefaction, the initial sand’s fabric (skeleton structure) formed during sedimentation process will be completely destroyed and changed during liquefaction and re-sedimentation process. Therefore, reliquefaction resistance is influenced by not only density but also structure change. To fully understand the mechanism of reliquefaction, this study focused on effects of sand particle orientation on deformation characteristics of sand in small to large strain range. The specimens were prepared using Toyoura sand with three initial depositional angles of 0°, 45°, and 90°. Then, two kinds of mechanical tests, those are bender element (BE) tests to measure initial shear modulus (G0) and local small-strain (LSS) tests to obtain secant shear modulus at various strain range were conducted using a triaxial apparatus. Two types of specimens, which are before liquefaction (without liquefaction history) and after liquefaction (with liquefaction history), were used in those tests. The particle orientations before and after liquefaction were measured using an image microscopy. The results obtained are follows. The BE tests showed increased G0 with increase of initial orientation angles (0° to 90°) before liquefaction. However, this trend became indistinct after liquefaction. Microscopic analysis for the particle orientation revealed that particle orientation tended to concentrate on 90° orientation in all cases after liquefaction. LSS test results additionally indicate degradation of secant G (Gsec) with shear strain is greater in the specimens with larger orientation angles. Those deformation characteristics had close relations with sand particle orientation.