Geotechnical Engineering Laboratory: Hoang Kim LE

Title: Liquefaction Characteristics of Sand Considering Particle Orientation

Supervisor: Hirofumi TOYOTA

Density, aging effects, and anisotropy induced by particle orientation are considered to be main factors that affect liquefaction resistance. Although various studies have been conducted on effects of density and aging effects on liquefaction, effects of anisotropy on liquefaction have not been completely clarified because of very limited studies. Therefore, in this study, we focus on the orientation of sand particles to investigate the effect of anisotropy on liquefaction.

Toyoura sand was used to prepare a specimen having some orientation of sand particles during its deposition. Then, saturated cyclic undrained triaxial tests (liquefaction tests) were conducted to determine the liquefaction resistance. In addition, shear strength tests (compression and extension) and bender element tests were conducted to examine their relationships with the liquefaction resistance. The orientation of sand particles before and after liquefaction was investigated using a microscopy to elucidate mechanism of anisotropy, which is appeared in mechanical properties of every kind. 

The results obtained are as follows:
1. The greater particle orientation angle is, the greater liquefaction resistance is obtained.
2. Based on triaxial extension tests, the shear strength increases in the order of deposition angle 0°, 45°, and 90°. From this result, extensional strength has greater effects than compressional strength on liquefaction resistance.
3. From the bender element tests, the initial shear modulus becomes greater as the particle orientation angle increases.
4. Comparing the particle orientation between before and after liquefaction, the orientation angle apparently increases after liquefaction.
5. The reliquefaction resistance, of which specimen ought to have a greater particle orientation angle, is smaller than the liquefaction resistance. This tendency is difficult to explain from the effects of particle orientation on liquefaction resistance, which is described in 1. Additional studies are necessary to elucidate the mechanism of reliquefaction.