Geoscience Reference
In-Depth Information
9 CONCLUSIONS
Reinforced walls (NCKU walls) that are 2.7m high were successfully constructed.
Long-termmonitoring on the behavior of thewall for 840 dayswas conducted. Itwas
shown that the pore pressure increase in the soil mass had a strong relationship with
the development of cracks or shear planes within the compacted clayey backfill. The
deformation of the facing was in an overturning mode, and might be caused by the
swelling of clay near the facing, the increase of pore water pressure in the tension
cracks, or the creep at the soil-reinforcement interface. A 1-m-high test
embankment using a compaction method similar to that used in the practice was
constructed to investigate the infiltration properties of compacted clay. The results of
the infiltration test at the crest of the embankment showed that the infiltration rate for
the clay compacted at 3%wet-of-optimumwas smaller than those compacted at 3%
dry-of-optimum and the optimum water content conditions. It was also shown that
thereinforcementsheetsmayraisethedegreeofcompactionfortheclayat3%wet-
of-optimum. FEM seepage analyses for unsaturated soil were performed to
investigate the in-situ permeability coefficients in vertical and horizontal directions.
It was shown that the permeability tests performed in-lab underestimated the
permeability coefficients significantly. Results from FEM seepage analyses for
NCKU walls indicated that cracks or shear planes always play a negative role in the
stability of the claywall, while geosynthetic composite layersmay play both positive
and negative roles depending on the initial pore pressure distributions in the backfill
and the boundary of the wall. Using an impermeable facing and an geo-drain layer
close to the crest of clay embankment could be an effective measure to mitigate the
development of saturated zones in the clayey backfill.
ACKNOWLEDGMENTS
This research is financially supported by the National Science Council,
Taiwan, R.O.C. under the contract nos. NSC 83-0209-E-006-022, NSC 85-2611-
E006-031, NSC 86-2611-E006-023, and NSC 87-2211-E006-052. The authors
appreciate the advice and the strong support fromProfessor K.S. Su, Department of
Civil Engineering, National Cheng Kung University, in setting up the test facility.
Grateful thanks are due to the San Lien Development Co., Ltd, for the technical
support on the monitoring system. The assistance fromMr F. J. Guo, and Mr J. M.
Jang, former graduate students at Cheng Kung University is also acknowledged.
REFERENCES
ASTM. D698-91: Test method for laboratory compaction characteristics of soil using
standard effort. 1994 Annual Book of ASTM standards, Vol. 04.08.
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