Hiroshi NAKAMURA
Effect of gravel content on shear modulus and liquefaction strength of gravel-mixed sand
Hirofumi TOYOTA
PS logging carried out in a borehole has been widely used for liquefaction potential mapping. Soundness evaluation system of the ground has been developed using the shear wave velocity, Vs, because Vs has a close relation with N-value or physical properties of soils. An undisturbed soil sample obtained by the freezing sampling is necessary to evaluate the liquefaction potential of the investigation ground. When other sampling methods are used, deformation modulus measured in a laboratory is usually smaller than that from PS logging because the sample is disturbed during transportation. Therefore, considering an ideal state without effects of aging and disturbance, specimen was made by an artificial method where gravel was mixed in sand in the laboratory. Then vender element (BE) tests and local small strain (LSS) tests were respectively conducted to measure Vs and deformation modulus. Various effects of gravel content and over-consolidation ratio (OCR) on liquefaction characteristics were experimentally examined with taking attention to wave propagation and small deformation properties.
The results obtained in the study are follows:
(a) Liquefaction characteristic of gravel-mixed sand
1. Strain progress and the number of cyclic loading to liquefaction hardly change in a range of 0% to 20% of gravel content. When the gravel content exceeds 30% in mass, liquefaction strength greatly increases. Therefore, there is a threshold value of gravel content against liquefaction strength.
(b) Wave propagation and small deformation characteristics of gravel-mixed sand
1. The effects of OCR on shear modulus, G0, were examined using BE and LSS tests. As a result, OCR has little influence on G0, because a clear difference of G0 was not appeared in the specimens between 1 and 4 of OCR.
2. In a range up to 30 % of gravel content, Gc, both values of G0 measured by BE and LSS tests were lineally increases with Gc. However, the value of G0 measured by BE test indicated a larger value than that by LSS test in a range larger than 30 % of Gc.
3. The change of G0 by Gc was able to explain using the collection equation of void ratio, which is used for the same soil having different void ratio. Therefore, when G0 without gravel is obtained, G0 of the real ground containing gravel can be estimated using G0 without gravel measured in the laboratory, when information of void ratio is obtained.
(c) Relation between liquefaction and small deformation characteristics including wave propagation
1. The liquefaction strength has close relation with a secant shear modulus of 0.003% shear strain. In other word, there is a possibility that liquefaction strength can be estimated using this kind of secant shear modulus.
2. Concerning gravel content of specimens, the liquefaction strength showed a linier relationship with the drained monotonic shear strength of the same specimen. However, there is no relation between the liquefaction strength and the drained monotonic shear strength of over-consolidated specimens.
Please use "previous botton" to return the previous page