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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
4. Under constant area replacement ratios, soil arching
becomes more effective as column diameters
decrease.
8 ACKNOWLEDGEMENTS
The authors would like to acknowledge the financial support
provided by the New Brunswick Innovation Foundation (NBIF)
and the University Research Fund (URF) of the University of
New Brunswick.
9 REFERENCES
Figure 5. Reduction in effectiveness of soil arching effects as column
diameter increases while maintaining a constant area replacement ratio
based on vertical stresses calculated near the top of the loose silt.
Abusharar S.W. and Han J. 2011. Two-dimensional deep-seated slope
stability analysis of embankments over stone column-improved soft
clay.
Engineering Geology
(120), 103-110.
GeoTech Systems Corporation. 1993. Styropor Technical Information.
Great Falls, Virginia, USA.
Hazarika H. 2006. Stress-strain modeling of EPS geofoam for large-
strain applications.
Geotextiles and Geomembranes
(24), 79-90.
6 DISCUSSION
Itasca. 2009.
FLAC
3D
Version 4.0 User Manuals
. Minnesota.
The results presented in this study revealed that sawdust is not
very beneficial as a standalone method as it is still reasonably
dense and highly compressible. As the strength of stone
columns is a result of both the friction characteristics of the
aggregate and the confinement from surrounding soils, in cases
where there is minimal confining pressure the columns will
deform (bulge) under the embankment loading. The anticipated
lateral loads in the stone columns should be considered to
confirm that there is adequate confinement within loose
cohesionless soils to prevent excessive internal deformation of
the column.
Jacobson J.R, Filz, G.M. and Mitchell J.K. 2003. Factors affecting
strength of lime-cement columns based on a laboratory study of
three organic soils.
Report VRTC 03-CR16
Virginia Transportation
Research Council, Charlottesville, Virginia, USA.
Kulhawy F.H and Mayne P. 1990.
Manual on Estimating Soil
Properties for Foundation Design.
Cornell University, Ithaca, New
York, USA.
Oliveira P.J, Pinheiro J.L.P and Correia A.A.A. 2011. Numerical
Analysis of an Embankment Built on Soft Soil Reinforced with
Deep Mixing Columns: Parametric Study.
Computers and
Geotechnics
(38), 566-576.
Deep mixed columns are very effective at reducing the
settlements due to the development of soil arching which is
clearly illustrated in the vertical stress plots where the stress
concentrations correspond with the midpoint of the columns
within the model. As shown in Figure 5 the soil arching is
increasingly effective as the diameter (and spacing) decrease. It
is anticipated that a limiting diameter exists where the diameter
will be controlled by the size of the mixing equipment that is
commercially available. Based on the analysis completed, for a
consistent area replacement ratio, the deep mixed columns
attract 35% more load due to soil arching than the
corresponding stone column.
Rowe R.K and Soderman K.L. 1984. Comparison of predicted and
observed behaviour of two test embankments.
Geotextiles and
Geomembranes
1 (2), 142-160.
Terzaghi K. 1943.
Theoretical Soil Mechanics
. New York, John Wiley
& Sons.
US Department of Transportation Federal Highway Administration
(FHWA). 2001.
Ground Improvement Technical Summaries
Volume I and II.
Publication No. FHWA-SA-98-086R.
Geofoam minimized settlements because it is so light in
comparison to other materials. With a density of 15 to 30 kg/m
3
it is substantially less dense than other light weight aggregates
such as sawdust which has a density of approximately
1040 kg/m
3
.
7 CONCLUSIONS
This study focused on just four types of methods used to
minimize overall settlements of embankments constructed on
loose silt but in future studies it would be interesting to compare
performances of columns (deep mixed or stone) vs panels of
columns at constant replacement ratios, and then to compare the
benefits of various replacement ratios. Increased lateral
confinement as a result of berms or sheet piles may also reduce
deformations, in addition to the use of geosynthetics for internal
structural support within the embankment, or a combination of
methods.
Based on the parametric analyses completed the following
guidelines are proposed which may be used to assist in the
selection of a method to reduce settlements.
1. The loose soil unit must be thick enough that there is
adequate confinement for stone columns to be
effective.
2. Deep mixed columns and geofoam may provide similar
final results if utilized in the correct quantities.
3. Under constant area replacement ratios, settlements
increase as column diameters increase.
