1112
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Figure 5. Gravimetric water content versus soil suction for Regina clay
preconsolidated to 6.125 kPa.
Figure 6. Gravimetric water content versus soil suction for
Regina clay preconsolidated to 49 kPa.
Figure 7. Gravimetric water content versus soil suction for
Regina clay preconsolidated to 392 kPa.
The laboratory SWCC test results on Regina clay illustrate
the need to separate gravimetric water content SWCC into two
components. Part of the change in water content is due to a
change in volume while the soil remains saturated. The other
part of the change in water content is associated with a change
in degree of saturation.
The proposed estimation procedure based on the SWCC and
the saturated hydraulic conductivity makes the assumption that
the reduction in hydraulic conductivity with suction is due to
desaturation of the soil. In other words, it is primarily the
increase in tortuosity upon desaturation of the soil that causes
the reduction in permeability. Prior to reaching the AEV of the
soil, volume change due to an increase in suction needs to be
accommodated in an independent manner.
Figure 8. Difference between the break in the gravimetric water content
SWCC and the Air-Entry Value for Regina clay.
The estimation of the permeability function with respect to a
change in suction can now be considered as having two
components; one component due to a change in void ratio and
the other components due to a change in the degree of
saturation. Further research should be undertaken to verify that
the unsaturated soil property functions can indeed be estimated
for all types of material by using the interpretation procedure
suggested in this paper.
7 CONCLUSIONS AND RECOMMENDATIONS
Changes in the volume of the soil specimens as soil suction is
increased can significantly affect the interpretation of the
SWCC. This paper presents a procedure that can be used to
independently consider the effects of volume change (where the
soil remains saturated) from the desaturation of the soil
specimen. The effects of volume change are shown to be
significant, resulting in erroneous calculations of the
permeability function for a soil.
8 REFERENCES
Fredlund, D. G., 1964. Comparison of soil suction and one-dimensional
consolidation characteristics of a highly plastic clay.
National
Research Council of Canada, Division of Building Research,
Technical Report No. 245
, Ottawa, Ontario, Canada.
Fredlund, D. G. 2002. Use of soil-water characteristic curve in the
implementation of unsaturated soil mechanics.
UNSAT 2002,
Proceedings of the Third International Conference on
Unsaturated Soils
, Recife, Brazil, March 10-13, pp. 887-904.
Fredlund, M. D., Wilson, G. W., and Fredlund, D. G. 2002.
Representation and estimation of the shrinkage curve.
UNSAT
2002, Proceedings of the Third International Conference on
Unsaturated Soils
, Recife, Brazil, March 10-13, pp. 145-149.
Fredlund, D. G., and Rahardjo, H. 1993.
Soil Mechanics for
Unsaturated Soils
. John Wiley and Sons, New York, N.Y.
Fredlund, D. G. and Xing, A. 1994. Equations for the soil-water
characteristic curve.
Canadian Geotechnical Journal
, 31(3): 521-
532.
van Genuchten, M. T. 1980. A closed-form equation for predicting the
hydraulic conductivity of unsaturated soils. Soil Science Society
of America Journal, Vol. 44, pp. 892-898.
