Stress–dilatancy behaviors of coarse granular soils in three-dimensional stress space

• The true triaxial tests were conducted to study the stress–dilatancy behaviors.
• The b-value could greatly influence the stress–dilatancy behaviors.
• A linear equation incorporating the effect of the b-value was proposed.
• The b-dependent stress–dilatancy equation could be useful in a constitutive model.

The influence of the intermediate principal stress ratio (i.e., the b-value) on the stress–dilatancy relation of coarse granular soils was investigated by a series of true triaxial compression tests conducted under the constant-p′ and constant-b loading conditions. It was observed that the peak and critical state friction angles increased with decreasing confining pressure or increasing b-value. An increase in the confining pressure or b-value resulted in a decrease in the maximum dilatancy angle. In addition, the relationship between the excess friction angle (i.e., the difference between the peak and critical state angles) and maximum dilatancy angle was greatly influenced by the b-value. A linear equation incorporating the effect of the b-value was proposed for this stress–dilatancy relationship. The perditions of the proposed equation could be in good agreement with the test data of coarse granular soils. The proposed b-dependent stress–dilatancy equation could be useful in the foundation of a constitutive model for granular soils.