Effects of loading rate and initial stress state on stress- strain behavior of rock fill materials under monotonic and cyclic loading conditions

This paper studies loading rate effect on stress–strain behaviors of high compacted rockfill materials. The large scale triaxial-dynamic equipment was used for this propose. To check the equipment capabilities, tests have been carried out on elastic spring and damping rubber specimens. The laboratory tests results indicate that the loading rate effect in elastic metal spring is negligible, while it has considerable effects on stress–strain behaviors in damping rubber, and especially in rockfill materials. The laboratory test results on rockfill materials have shown that dry specimens have higher E and D values compared to the saturated samples. Anisotropic specimens have higher Young’s modulus and less damping ratio in comparison to isotropic samples. Generally, the influence of the main parameters on E and D in rockfill specimens is initial vertical effective stress and loading frequency, respectively. The high compacted rockfill specimen exhibits a non-destructive response to the application of cyclic loading below a threshold axial strain level of <0.005%. Since the frequency effect was observed in the strain levels lower than 0.005%, and there is not meaningful build up of pore pressure in this strain level, therefore any effect of excess pore water pressure on the frequency effect is negligible.