Katsunobu TOYOSHIMA
Effects of gravel shape on shear modulus and liquefaction strength in gravel-mixed sand
Hirofumi TOYOTA
Liquefaction generally occurs in the sandy ground, which has loose sedimentation and high
groundwater level. However, it has been reported that liquefaction occurred in gravelly ground
during the 1995 Kobe Earthquake. Nevertheless, few studies have been conducted on liquefaction of
gravelly soil. Although a pre-loading method has been also reported to be effective as
countermeasures against liquefaction, the mechanism to prevent the liquefaction is unclear because
the method was developed for soft clayey ground against ground subsidence. Therefore, it is
important that liquefaction evaluation technique is developed in the ground having wide range of
particle size and stress history. Various effects of gravel shape (pebble and rubble), gravel content
and overconsolidation ratio (OCR) on liquefaction were examined with taking attention to wave
propagation, small deformation properties, and the relevance of each properties.
The results obtained in the study are follows:
(a) Liquefaction characteristic of gravel-mixed sand
1. When gravel content exceeds 20% in mass, liquefaction strength greatly increases.
2. If gravel content is less than 10%, liquefaction strength is independent on gravel shape. When
gravel content reaches 20%, the liquefaction strength in the rubble-mixed sand becomes larger than
that in the pebble-mixed sand.
3. The liquefaction strength increases by overconsolidation. This effect is stronger in order of the
rubble-mixed sand, the pebble-mixed sand and only sand specimens.
(b) Wave propagation and small deformation properties related to liquefaction strength
1. The liquefaction strength has close relation with a secant shear modulus of about 0.02% shear
strain. Therefore, there is a possibility that liquefaction strength can be precisely estimated using this
kind of secant shear modulus.
2. The shape of normalized G-¦Ås relations, where a secant shear modulus is normalized by an initial
shear modulus, only depends on the OCR. A technique to estimate liquefaction strength in the
ground was proposed using this relation and Vs obtained from in-situ investigation.
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