Bimodal Shear-Strength Behavior of Unsaturated Coarse-Grained Soils
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 139, Issue 12
Abstract
The microstructure, compressibility, and shear strength of an unsaturated widely graded coarse soil were investigated through a series of laboratory tests. The results show that coarse soil has a dual-porosity structure that has both intra- and interaggregate pores. The soil-water characteristic curve (SWCC) shows bimodal features. Accordingly, the shear strength and compressibility over the entire suction range also show two distinct modes. The pore water drains from the interaggregate pores in the first mode while the intraaggregate pores remain saturated. The shear-strength behavior during this drainage period resembles that of uniform coarse sand. The apparent cohesion reaches a peak and then decreases with increasing suction, whereas the compressibility decreases first and then increases. The clay aggregates become unsaturated in the second mode as the pore water drains from the intraaggregate pores. The compressibility decreases and the apparent cohesion increases with suction as in a typical fine-grained soil. A shear-strength model is proposed for granular soils with a bimodal SWCC. The proposed equation can also be degenerated to predict the shear strength of a wide range of soils.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The authors acknowledge the support from the Research Grants Council of the Hong Kong SAR (Grant No. 622210).
References
Alonso, E. E., Gens, A., and Josa, A. (1990). “A constitutive model for partially saturated soils.” Geotechnique, 40(3), 405–430.
ASTM. (2000). “Standard test method for laboratory compaction characteristics of soil using standard effort.” D698-07e1, West Conshohocken, PA.
ASTM. (2002). “Standard practice for classification of soils for engineering purposes (unified soil classification system).” D2487, West Conshohocken, PA.
Brooks, R. H., and Corey, A. T. (1964). Hydraulic properties of porous media, No. 3, Colorado State Univ., Fort Collins, CO.
Burger, C. A., and Shackelford, C. D. (2001). “Soil-water characteristic curves and dual porosity of sand-diatomaceous earth mixtures.” J. Geotech. Geoenviron. Eng., 127(9), 790–800.
Cui, Y. J., and Delage, P. (1996). “Yielding and plastic behavior of an unsaturated compacted silt.” Geotechnique, 46(2), 291–311.
Fisher, R. A. (1926). “On the capillary forces in an ideal soil; correction of formulae given by W. B. Haines.” J. Agric. Sci., 16(3), 492–505.
Fredlund, D. G., Morgenstern, N. R., and Widger, R. A. (1978). “Shear strength of unsaturated soils.” Can. Geotech. J., 15(3), 313–321.
Fredlund, D. G., and Rahardjo, H. (1993). Soil mechanics for unsaturated soils, Wiley, New York.
Fredlund, D. G., and Xing, A. (1994). “Equations for the soil-water characteristic curve.” Can. Geotech. J., 31(4), 521–532.
Fredlund, D. G., Xing, A., Fredlund, M. D., and Barbour, S. L. (1996). “The relationship of unsaturated soil shear strength to the soil-water characteristic curve.” Can. Geotech. J., 33(3), 440–448.
Gallipoli, D., Gens, A., Sharma, R., and Vaunat, J. (2003). “An elasto-plastic model for unsaturated soil incorporating the effects of suction and degree of saturation on mechanical behavior.” Geotechnique, 53(1), 123–135.
Gan, J. K., Fredlund, D. G., and Rahardjo, H. (1988). “Determination of the shear strength parameters of an unsaturated soil using direct shear test.” Can. Geotech. J., 25(3), 500–510.
Guan, G. S., Rahardjo, H., and Choon, L. E. (2010). “Shear strength equations for unsaturated soil under drying and wetting.” J. Geotech. Geoenviron. Eng., 136(4), 594–606.
Han, K. K., Rahardjo, H., and Broms, B. B. (1995). “Effect of hysteresis on the shear strength of a residual soil.” Proc., 1st Int. Conf. on Unsaturated Soil, Vol. 2, Balkema, Rotterdam, Netherlands, 499–504.
Ho, D. Y. F., and Fredlund, D. G. (1982). “A multi-stage triaxial for unsaturated soils.” ASTM Geotech Test. J., 5(1–2), 18–25.
Houston, S. L., Perea-Garcia, N., and Houston, W. N. (2008). “Shear strength and shear-induced volume change behavior of unsaturated soils from a triaxial test program.” J. Geotech. Geoenviron. Eng., 134(11), 1619–1632.
Juang, C. H., and Holtz, R. D. (1986). “Fabric, pore size distribution, and permeability of sandy soils.” J. Geotech. Engrg., 112(9), 855–868.
Khalili, N., and Khabbaz, M. H. (1998). “A unique relationship for the determination of the shear strength of unsaturated soils.” Geotechnique, 48(5), 681–687.
Kim, W. S., and Borden, R. H. (2011). “Influence of soil type and stress state on predicting shear strength of unsaturated soils using the soil-water characteristic curve.” Can. Geotech. J., 48(12), 1886–1900.
Ladd, R. S. (1978). “Preparing test specimens using undercompaction.” ASTM Geotech Test. J., 1(1), 16–23.
Lee, I. M., Sung, S. G., and Cho, G. C. (2005). “Effect of stress state on the unsaturated shear strength of a weathered granite.” Can. Geotech. J., 42(2), 624–631.
Leong, E. C., and Rahardjo, H. (1997). “A review of soil-water characteristic curve equations.” J. Geotech. Geoenviron. Eng., 123(12), 1106–1117.
Li, X., and Zhang, L. M. (2009). “Characterization of dual-structure pore-size distribution of soil.” Can. Geotech. J., 46(2), 129–141.
Li, X., Zhang, L. M., and Li, J. H. (2009). “Development of a modified axis translation technique for measuring SWCCs for gravel soils at very low suctions.” ASTM Geotech Test. J., 32(6), 1–11.
Likos, W. J., and Lu, N. (2004). “Hysteresis of capillary stress in unsaturated granular soil.” J. Eng. Mech., 130(6), 646–655.
Likos, W. J., Wayllace, A. W., Godt, J. G., and Lu, N. (2010). “Modified direct shear apparatus for unsaturated sands at low suction and stress.” ASTM Geotech Test. J., 33(4), 1–13.
Ng, C. W. W., Zhan, L. T., and Cui, Y. J. (2002). “A new simple system for measuring volume changes in unsaturated soils.” Can. Geotech. J., 39(3), 757–764.
Oberg, A., and Sallfors, G. (1997). “Determination of shear strength parameters of unsaturated silts and sands based on the water retention curve.” ASTM Geotech Test. J., 20(1), 40–48.
Rassam, D. W., and Williams, D. J. (1999). “A relationship describing the shear strength of unsaturated soil.” Can. Geotech. J., 36(2), 363–368.
Sheng, D. C., Zhou, A. N., and Fredlund, D. G. (2011). “Shear strength criteria for unsaturated soils.” Geotech. Geologic. Eng., 29(2), 145–159.
Thu, T. M., Rahardjio, H., and Leong, E. C. (2007a). “Critical state behavior of a compacted silt specimen.” Soils Found., 47(4), 749–755.
Thu, T. M., Rahardjio, H., and Leong, E. C. (2007b). “Soil-water characteristic curve and consolidation behavior for a compacted silt.” Can. Geotech. J., 44(3), 266–275.
Toll, D. G., and Ong, B. H. (2003). “Critical state parameters for an unsaturated residual sandy clay.” Geotechnique, 53(1), 93–103.
van Genuchten, M. T. (1980). “A closed-form equation predicting the hydraulic conductivity of unsaturated soils.” Soil Sci. Soc. Am. J., 44(5), 892–898.
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.” Can. Geotech. J., 33(3), 379–392.
Wang, Y. H., and Siu, W. K. (2006). “Structure characteristics and mechanical properties of kaolinite soils. I. Surface charges and structural characterizations.” Can. Geotech. J., 43(6), 587–600.
Wheeler, S. J., and Sivakumar, V. (1995). “An elasto-plastic critical state framework for unsaturated soil.” Geotechnique, 45(1), 35–53.
William, J. L., Wayllace, A., Godt, J., and Lu, N. (2010). “Modified direct shear apparatus for unsaturated sands at low suction and stress.” ASTM Geotech Test. J., 33(4), 1–13.
Zhang, L. L., Fredlund, D. G., Zhang, L. M., and Tang, W. H. (2004). “Conditions under which soil suction can be maintained.” Can. Geotech. J., 41(4), 569–582.
Zhang, L. M., and Chen, Q. (2005). “Predicting bimodal soil-water characteristic curves.” J. Geotech. Geoenviron. Eng., 131(5), 666–670.
Zhang, L. M., and Li, X. (2010). “Microporosity structure of coarse granular soils.” J. Geotech. Geoenviron. Eng., 136(10), 1425–1436.
Zhao, H. F., Zhang, L. M., and Chang, D. S. (2013). “Behavior of coarse widely graded soil under low confining pressures.” J. Geotech. Geoenviron. Eng., 139(1), 35–48.
Information & Authors
Information
Published In
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Apr 30, 2012
Accepted: Mar 29, 2013
Published online: Apr 3, 2013
Published in print: Dec 1, 2013
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.