P15

Microscopic Study of Factors Affecting Liquefaction Strength
during Anisotropic Consolidation〇Yusong HAN, Ryosuke UZUOKA, Kyohei UEDA, Manta NAKAMURAstress ratios (CSR) τmax/p’ 0 ranging from 0.225 to

1. Introduction
Conventional triaxial tests have been extensively

0.375 until liquefaction occurred.

conducted to elucidate the mechanisms of liquefaction.
During earthquakes, vertically propagating shear
waves rotate the axes of principal stress in soil
elements, resulting in different stress states from thosein triaxial tests. To address the limitations oftraditional experiments, alternative testing methods,
including hollow torsional shear tests [1] were utilized
to study liquefaction. This study proposed a novel
approach for simulating undrained hollow torsional

Fig. 1. Specimen and apparatus in simulationdR

tests using the discrete element method (DEM). It

dt

offered a microscopic perspective on how initial

=r dr

R dt

(1)

3. Results and discussion

anisotropy influences the liquefaction strength.
2. Methodology

Fig. 2 depicts the relationship between deviatoric

The initial boundary conditions, as shown in Fig. 1,stress σvM and mean principal stress p’ during theinvolve two rigid cylinders with an inner diameter of 6liquefaction process, and a typical stress evolution in

cm and an outer diameter of 10 cm. The upper andlaboratory tests has been replicated in DEM

lower

apart.

simulations, providing evidence for the effectiveness

Additionally, 6 blades designed for applying shearof the method proposed. Fig. 3 shows that anforces are positioned on the two ends of the apparatus

increasing initial stress anisotropy induced lower

boundaries

arelocated10cm

To obtain anisotropically consolidated specimens,triaxial compression (K0 < 1.0) and extension (K0 >liquefaction resistance strength.
The coordination number (Z) serves as an indicator1.0) shear tests were conducted on isotropic

reflecting the

microscopic densityof granularspecimens under constant-p' condition. 10 cases ofmaterials. Fig. 4 shows the evolution of Z underanisotropically consolidated specimens with K0 values

different initial stress states during the liquefaction

ranging from 0.3 to 3.33 were obtained. As indicatedprocess, and the the relationship between Z and theby Eq. (1), the variation of the outer and inner radii R

number of cycles required to trigger liquefaction (NL).

and r was controlled proportionally to ensure aThe result indicates that initial Z contributes to theconstant volume of the specimen, and t denotes time.

liquefaction resistance strength, and the preliminary

Specimens with initial K0 values ranging from 0.33 totriaxial shear produces a lower Z, thus reducing the3.33 were subjected to shear forces with 7 differentliquefaction strength.

oftheextension

statewithinitialK0=2.0,

characterized by a dimpled disk oriented toward theaxis. As cyclic shear proceeds, the direction ofmaximum

contact

densitycontinuously

variesfollowing the rotating major principal stress axis, andthe overall contact density gradually decreases. The
post-liquefaction distribution of contact density isalmost independent of the initial state, shifting
Fig. 2. Relationship between σvM and p’

between two columnar distributions in differentdirections.

Fig. 3. Liquefaction resistance strength
Contact density is defined as the mathematical
expectation of the average number of contacts per unit

Fig. 4. Evolution of Z and relationship between Z

surface area in all orientations for one particle. Fig.

and NL5(a) represents the state with initial K0=0.5, exhibiting

4. Referencesa elongated morphology extending toward the axialdirection, whereas Fig. 5(b) depicts the contact density[1]Vargas, R. et al.(2020). Soil Dynamics andEarthquake Engineering, 133, 106111.

(a) Anisotropic state with K0 = 0.5(b) Anisotropic state with K0 = 2.0
Fig. 5. Comparison of contact density evolution in liquefaction process with different initial K0