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

This paper studies loading rate effect on stressstrain behaviors of high compacted rockfillmaterials. the large scale triaxial-dynamic equipment was used for this propose. to check the equipmentcapabilities, tests have been carried out on elastic spring and damping rubber specimens. the laboratorytests results indicate that the loading rate effect in elastic metal spring is negligible, while it hasconsiderable effects on stressstrain 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 dvalues compared to the saturated samples. anisotropic specimens have higher young's modulus and lessdamping ratio in comparison to isotropic samples. generally, the influence of the main parameters on eand d in rockfill specimens is initial vertical effective stress and loading frequency, respectively. the highcompacted rockfill specimen exhibits a non-destructive response to the application of cyclic loading belowa threshold axial strain level of < 0.005%. since the frequency effect was observed in the strain levels lowerthan 0.005%, and there is not meaningful build up of pore pressure in this strain level, therefore any effectof excess pore water pressure on the frequency effect is negligible.