General Stress–Dilatancy Relation for Granular Soils
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 142, Issue 4
The stress–dilatancy relation is a significant component in modeling the stress-strain behavior of soils, and reflects the relationship between the excess friction angle (i.e., the difference between peak and critical state angles ) and the maximum dilatancy angle . The stress–dilatancy relation can be expressed as , in which is a coefficient. Bolton (1986) found and 0.8 for clean sands under the conventional triaxial condition [i.e., , where ] and plane-strain (PS) condition (), respectively, which indicates that is dependent on the -value. However, the stress–dilatancy relation of soils (especially coarse granular soils) for the whole range of the -values (i.e., ) has not been fully investigated. In addition, a general formulation is needed for this relationship.
Three categories of true triaxial tests were conducted for dense coarse granular soils (CGSs) with the same initial gradation and the same maximum diameter of 10 mm. The C1 tests were conducted for angular particle soils sheared under constant- and constant- conditions (). The C2 tests were conducted for angular particle soils sheared under constant- and constant- conditions (). The C3 tests were conducted for rounded particle soils sheared under constant- and constant- conditions (). Five different -values (, 0.25, 0.5, 0.75, and 1) were applied. Detailed descriptions of the true triaxial apparatus, specimen preparation, and test procedures were reported by Xiao et al. (2014).
Fig. 1 shows that the value of is related to the -value, indicating that a -dependent stress–dilatancy relation is observed for CGSs. A general stress–dilatancy relation for CGSs can be written aswhere material constants (= 1.7), (= 1.36), and (= 0.72) can be obtained from the relationship between and . Fig. 2 shows that Eq. (1) can accurately predict the test data for soils with different particle angularity and shearing conditions.
(1)
Implications
The stress–dilatancy relation for CGSs is dependent on the -value, and a general expression for this relationship has been proposed. The ratio of under and (i.e., the approximate PS condition) is 0.6 for CGSs, which is identical to that for clean sands (Bolton 1986). The general stress–dilatancy relation can be applicable for different granular soils, although the material constants may change as a result of, e.g., soil particle size, gradation, and mineralogy. In addition, the expression could be used in the plastic flow rule to characterize the strength, dilation, and stress-strain behavior of granular soils in three-dimensional stress space.
Acknowledgments
The authors would like to acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51509024).
References
Bolton, M. D. (1986). “The strength and dilatancy of sands.” Geotechnique, 36(1), 65–78.
Xiao, Y., Liu, H., Chen, Y., and Zhang, W. (2014). “Particle size effects in granular soils under true triaxial conditions.” Geotechnique, 64(8), 667–672.
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© 2016 American Society of Civil Engineers.
History
Received: Oct 13, 2015
Accepted: Nov 25, 2015
Published online: Jan 21, 2016
Published in print: Apr 1, 2016
Discussion open until: Jun 21, 2016
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