Abstract: In view of the problem that the creep damage of pillar under the effect of long-term in-situ stress is affected by its water content in the process of mining， creep tests of sandstone under step-loading under dry， immersed and saturated conditions were carried out. Based on ultrasonic tests， the ultrasonic characteristics of water-bearing rock during creep process are analyzed to explore the time effect of water on rock mechanical property degradation. The influence of water-bearing state on creep failure characteristics of sandstone is studied， and the precursor and time rule of creep failure of water-bearing pillar was revealed. The variations of ultrasonic wave velocity， dominant frequency and amplitude in the loading process were discussed， based on the ultrasonic test during creep processes of dry and saturated sandstones under multi-stage loads. The results showed that with the increase of stress level， the dominant frequency and amplitude of dry and saturated samples are reduced， resulting in a phenomenon termed with "frequency drift"， and the water-bearing sandstone shows a low-pass filtering characteristic. The damage of saturated sandstone is greater than that of dry rock. Influences of initial water-bearing state on creep deformation and its rate were obtained. The failure time arrives earlier and stress levels are lower， for the immersed and saturated groups. Before the specimens are destroyed， there is an inflection point where the creep strain increases slowly and then dramatically， and the specimens are destroyed within 0.5 hour after the creep strain beyond the inflection point. The creep failure modes of dry， immersed， and saturated sandstones are X-shape failure， entire fragmented blocks， and tensile failure along axis， respectively.

Key words: dry and saturated, immersion experiment, creep by multi-staged loads, ultrasonic wave, damage representation