Study on creep behaviour of sandstone and its mechanical models

Creep of rock could be influenced by a few factors and the stress states had great influence on the rheological characters of soft rock.The uniaxial compressive creep test on sand stone showed that,when the stress was considerably less than yield stress,the decreasing strain rate approached to a final steady value.In this case the creep was named stable creep and only got to the phase 1 and 2 without damage.On the other hand,when the stress was close to the yield stress,the strain rate decreased at the beginning,then accelerated to increase.Crack appeared and spread in the 3rd phase of the creeping process.The destructing pattern is tensive crack,which belonged to unsteady creeping.It was shown that yield stress was a critical value to cause unsteady creeping.An emperical constitutive model and the creep stress model were established according to the differences of creep induced by the stress level.