1092
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
6 SUMMARY AND CONCLUSIONS
The matric suction applied in the tests described in this paper
was controlled using an improved volumetric pressure plate
extractor (VPPE) system to simulate unsaturated conditions
near the soil surface. The VPPE was improved for the
application of the axial load. The elastic moduli and void ratios
of the two unsaturated soils tested were determined using
compression and shear waves. The compression waves were
continuously measured by piezo disk elements and the shear
waves were monitored by bender elements. The piezo disk
elements and bender elements were installed on the wall of the
confining cell. Two types of specimens were used: a sand
specimen and a sand
–
silt mixture specimen with a silt volume
fraction of 20%. Axial stresses of 100 and 350 kPa were applied
to the sand specimen and the sand
–
silt specimen, respectively.
The compression and shear wave velocities of the sand
specimen remained almost constant for degrees of saturation
from 15 to 80%. The compression wave velocity for the sand
–
silt mixture specimen also remained constant, but the shear
wave velocity increased as the degree of saturation decreased.
As the applied axial stress increased, the compression wave
velocity increased. The void ratios determined from the elastic
wave velocities agreed well with the volume-based void ratios.
The results of this study suggest that elastic waves can be
effectively used to estimate the void ratio and elastic moduli of
unsaturated soils.
7 ACKNOWLEDGEMENTS
This work was supported by the National Research Foundation
of Korea (NRF) grant funded by the Korea government (MEST)
(No. 2012-0005729).
8 REFERENCES
Fredlund, D. G., Morgenstern, N. R., and Widger, R. A. 1978. The shear
strength of unsaturated soils.
Canadian Geotechnical Journal
15(3),
313-321.
Fredlund, D. G., Rahardjo, H. 1993.
Soil mechanics for unsaturated
Soils
. John Wiley & Sons, Inc.
Fredlund, D. G., Xing, A. 1994. Equations for the soil-water
characteristic curve.
Canadian Geotechnical Journal
31(4), 521-
532.
Lee, C., Lee, J. S., Lee, W., and Cho, T. H. 2008. Experiment setup for
shear wave and electrical resistance measurements in an oedometer.
Geotechnical Testing Journal, ASTM,
31(2), 149-156.
Lee, J. S. and Santamarina J. S. 2005. Bender elements: performance
and signal interpretation.
ASCE, Journal of Geotechnical and
Geoenvironmental Engineering
, 131(9), 1063-1070.
Lee, J. S. and Santamarina J. S. 2005.
Discussion “Measuring
shear
wave velocity using bender e
lements” By Leong, E. C., Yeo, S.
H.,
and Rahardjo, H. (Geotechnical Testing Journal, V0 l. 28, No. 5),
Geotechnical Testing Journal, ASTM
. 29(5), 439-441.
Lee, J. S., Lee, C. Yoon, H. K., Lee, C., and Lee, W. 2010. Penetration
type field velocity probe for soft soils.
ASCE, Journal of
Geotechnical and Geoenvironmental Engineering,
136 (1), 199-
206.
Matyas, E. L., and Radhakrishna, H. S. 1968. Volume change
characteristics of Partially Saturated Soils.
Geotechnique
18(4),
432-448.
Vanapalli, S. K., Fredlund, D. G., Pufahl, D. E., and Clifton, A. W.
1996. Model for the prediction of shear strength with respect to soil
suction.
Canadian Geotechnical Journal
33(3), 379-392.
Yoon, H. K., and Lee, J. S. 2010. Field velocity resistivity probe for
estimating stiffness and void ratio.
Soil Dynamics and Earthquake
Engineering
30(12), 1540-1549.
