Actes du colloque - Volume 3 - page 756

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Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
The figures show that the shear induced pore pressures were
found to be less in specimens which had the smear zone
surrounding the sand column. Due to the smear zone, these
pore pressures within the SCP were reduced because the water
was not permitted to flow towards the column during shearing.
6. REFERENCES
This was also evident from Scanning Electron Microscope
(SEM) images (Fig. 6a-b) taken on post shear tests of specimens
with and without smear. The images of samples with and
without the smear zone show differences in the microstructure.
The clay minerals in the smear zone appear to be closely packed
with reduced pore space. 7.5 mm x 7.5 mm x 7.5 mm air dried
samples were prepared at room temperature for the SEM
images.
Aboshi, H. and Suematsu, N. (1985). Sand compaction pile method:
State-of-the art paper. Proceedings of the 3rd International
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Aboshi, H., Ichimoto, E., Enoki M. and Harada, K. (1979). Composer:
method to improve characteristics of soft clays by inclusions of
large diameter sand column. Proceedings of the International
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Asaoka, A., Kodaka, T. and Nozu, M. (1994). Undrained shear strength
of clay improved with sand compaction piles. Soils and
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Figure 6. SEM images: (a) Composite samples without smear zone; and
(b) Composite samples with smear zone.
4. CONCLUSIONS
The strength behavior of composite ground reinforced with sand
compaction piles has been studied using 20 consolidated
undrained triaxial tests. Vertical stress of the sand column was
examined when the composited specimens were tested to failure
in conventional triaxial tests. The test results suggest that the
stress-strain behavior of the clay was influenced by the presence
of smear zone. It seems clear that the presence of smear zone
has reduced the ultimate undrained shear strength by 25%.
SEM images indicated that the natural fabric of the soil was
destroyed adjacent to the SCPs with smear zone which in turn
affected pore pressure response of the composite soil sample.
Specimens sheared with smear effect appear closely packed and
more homogeneous with partly discernible particle systems,
while specimen without smear condition indicate a distinct
division between smaller intra-aggregate pore spaces and the
larger inter-aggregate voids. Shear induced pore pressures were
less in soil specimens with smear-effect because the water was
not permitted to flow towards the column during shearing. It
was postulated that the difference in the behavior of smear and
non-smear specimens was because that the pore pressure
measurements were taken within the sand column. This
difference was not apparent when 80mm diameter SCP with
smear zone was used. These changes affect the effective
horizontal stress in the clay and hence the load carried by the
individual sand columns.
Matsuda, H., Fujiwara, Takahasi, S. and Kitayama, M. (1997).
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Mir, B. A. (2010). Study of the influence of smear zone around sand
compaction pile on properties of composite ground. Ph.D. Thesis,
IIT Bombay.
Singh, G. and Hattab, T. N. (1979). A laboratory study of efficiency of
sand drains in relation to methods of installation and spacing.
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Randolph, M. F., Carter, J. P. and Wroth, C. P. (1979). Driven piles in
clay-the effects of installation and subsequent consolidation.
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Schofield, A. N. and Wroth, C. P. (1968). Critical State Soil
Mechanics. MacGraw-Hill, London, p. 218.
Xu, X. T., Liu, H. L. and Lehane, B. M. (2006). Pipe pile installation
effects in soft clay. Proceedings of the Institution of Civil
Engineers, Geotechnical Engineering 159, Issue GE4 pp. 285-296.
Weber, T. M., Plotze, M., Laue, J., Peschke, G. and Springman, S. M.
(2010). Smear zone identification and soil properties around stone
columns constructed in-flight in centrifuge model tests.
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5. ACKNOWLEDGEMENT
The first author would like to acknowledge the financial support
from the Indian Institute of Technology Bombay (IITB) in the
form of research scholarships.