Stress and deformation behaviors of rockfill under cyclic loadings

Based on a series of static and dynamic tri-axial tests on different rockfill, the special stress and deformation behaviors of rockfill are revealed. It is found that the classic Rowe's stress dilatancy theory will be obviously underestimated by the relevant constitutive models established based on the Rowe's theory. Being not straight, in the p-q plane, the dilantancy line Md buckles to the upper-left, while the failure line Mf is slightly bent to the top-left. With the increase of the stress level, Md will be gradually close to and even exceed Mf. The permanent shear deformation and volume deformation accordingly increase with the increase of the ratio of dynamic stress to cell pressure; differently with the increase of ever shear volume, the volume deformation accordingly decreases with the increase of consolidation stress ratio. In the first cycle of cyclic loadings, the accretion of permanent shear deformation and volume deformation is larger than that of standard sand, and with the increase of cycles, the hardening of the rockfill is also more evident. During the dynamic tests, shrinkage occurs instead of dilantancy no matter what pedogenic rock and gradation are. There obviously occurs particle breakage during consolidation, static and dynamic tri-axial tests. The ratio of particle breakage has close relation with the pedogenic rock, gradation and cell pressure. In the static tri-axial tests, the ratio of particle breakage increases with the increase of the cell pressure, but decreases in the dynamic ones. Obviously, the particle breakage will decrease the shear dilantancy and increase the shear shrinkage. The special failure mechanism of rockfill and the shear dilantancy have close relation with the particle breakage. Previous cyclic loading will obviously raise the capability of resistance of rockfill to the deformation.