Stress-state Dependency of the Strain Ratio of Quasi-Elastic Granular Soils under Cyclic Loading

Poisson’s ratio, besides its transverse–axial strain ratio definition, also plays a significant role in traditional elastic theory as an elastic constant. However, this elastic role of Poisson’s ratio faces a challenge when applied to granular soils. A so-called “strain ratio” is therefore introduced and measured in this paper for granular soils under quasi-elastic state. With the same definition of the transverse–axial strain ratio as Poisson’s ratio, the strain ratio is investigated under cyclic triaxial tests for its stress-state dependency. The results show that Poisson’s ratio is consistent with strain ratio only in the initial state of shear, and there is a non-negligible deviation in subsequent shear. The conversion relationship of elastic constants does not hold for the strain ratio with increasing deviator stress. A special case is analyzed when the strain ratio is greater than 0.5 and the specimen is subject to a quasi-elastic shear dilatancy. Discrete element simulations are conducted to clarify the microscopic mechanism of quasi-elastic dilatancy by tracking the evolution of the contact number of particles and the trajectory of the contact. This study provides new insights in understanding the elastic behavior of granular soils.