A study of the time-dependent deformation of sedimentary rock



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Creep tests performed on Berea Sandstone and Indiana Limestone suggest that strain rates developed early in the deformational history of the rocks can be used to predict the time to onset of accelerating creep at which catastrophic failure of the rock is imminent. For both rock types, tested dry under uniaxial compression at room temperature, the variables secondary (steady-state) strain rate ( g ) and time to onset of tertiary creep (Tc)n follow an empirically determined power law of the form [epsilon]s = K(Tc)n where K and n are material constants. The data base includes both single-load and multiple-load creep tests for each rock type. The average strength of the Multiple Increment Creep Test (MICT) limestone samples is found to exceed the average strength of the Single Increment Creep Test (SICT) limestone samples, indicating that longterm loading increases the ultimate strength of the limestone. On the other hand, the average strength of the MICT sandstone samples is less than the average strength of the SICT sandstone samples, indicating that the ultimate strength of the sandstone is decreased under long-term loading.