2Associate professor, shahrood university of technology
3Professor, shahroodu university of technology
4Independent engineer, KBB underground
Creep phenomenon in rock engineering plays a key role in development of underground spaces as they must be stable enough for a long period of time. Current research involved designing and manufacturing of a new creep testing machine. The equipment is capable to perform simultaneous light-duty creep tests on more than one cylindrical rock samples at a very low cost. To evaluate the equipment’s performance, a series of creep test was performed on salt rock samples and their axial and lateral deformations were measured by dial gauges. Measurements were taken under constant temperature, humidity and sustained loads. The results revealed that the creep rate in lateral direction was far greater than in the axial direction. Another important conclusion was that both axial and lateral creep curves follow the same pattern with an idealized salt rock creep curve. Also, experiments indicated that the steady state creep rate increases with increasing initial stress state. Also, initial stress state showed a great influence on salt primary creep response.