Experimental study on strength and deformation of filling materials of super-high dams with wide confining pressures under loading and unloading conditions

The triaxial tests with wide confining pressures under loading and unloading conditions are carried out to study the strength and deformation of filling materials of super-high dams. It is found that the strength under low confining pressure of sand gravel is lower than that of rockfill materials, so the slope of dams filled with sand gravel should be gentler to prevent instability. The range of confining pressure has great effects on the strength indexes and deformation parameters. The change of nonlinear strength index is not as significant as that of linear strength index, and the change of nonlinear strength index of sand gravel is not as significant as that of rockfill. For a super-high dam, different strength indexes and deformation parameters should be adopted according to the stress distribution of dam crest, dam slope and dam body. The axial and volume deformations occur during unloading-reloading cycle, and after the cycle the curves of stress-strain and volumetric strain-axial deformation return to normal shape. During unloading, the volume of samples mainly seems to expand under low confining pressures and stress level, and contracts under high confining pressures. During the reloading stage, the volume deformation mainly shows shear shrinkage regardless of the confining pressure or stress level. The ratio of resilient modulus to initial tangent modulus increases with the confining pressure, and the resilient modulus seems to decrease with the stress level. The the ratio of K_ur/K is about 1.98~2.22, but the resilient modulus index $n_{\text{ur}}$ is larger than the initial tangent one $n$.