Scale Effects in the Creep Parameters of Fractured Rock Masses

The influence of scale effects on the creep parameters of fractured rock masses are investigated through a series of in-situ and laboratory creep tests on slate and claystone. An in-situ creep test on slate indicates that deformation is highly heterogeneous, and that this resulting heterogeneous differential flow deformation is the primary cause for the failure. Creep tests on claystone define the magnitude of scale effects on the resulting creep parameters, including initial creep stress, long-term strength, deformation modulus, and viscosity, and also on the mode of ultimate failure. These parameters are correlated against specimen size, as indexed through the number of component blocks in the test specimens. These resulting empirical relations provide a defensible method for upscaling to field scale.