In order to analyze the feasibility of a single specimen used for step-loaded relaxation tests and study the time dependent stress relaxation properties of rockfill，two types of the drained triaxial compression tests were carried out with large-scale triaxial apparatus for rockfill. One is the constant-strain-rate triaxial compression tests, and the other is the step-loaded drained triaxial relaxation tests under different confined pressures and strain levels. A hyperbolic function was presented to simulate the laws of stress relaxation. The results show that the relaxation phases have little effect on stress-strain behavior at subsequent constant-strain-rate triaxial compression tests. This means a single specimen can be used reliably for step-loaded relaxation tests. The volumetric strain increase is 0.13％～0.71％ and the magnitude of stress decrease is 16％～28％ during relaxation phases. The rockfill can sustain a constant, nonzero value of deviator stress in the end. The laws of stress relaxation of rockfill can be simulated by the hyperbolic functions reasonably. Parameters analyses show that the decay of the deviator stress rate at the initial time is a constant value, independent of the confined pressure and the strain level.
