Discrete Element Modelling of Rock Creep Behaviour using Rate Process Theory

Rock creep behavior is crucial in many rock engineering projects. Different approaches have been proposed to model rock creep behavior; however, many cannot reproduce tertiary creep (i.e., accelerating strain rates leading to rock failure). In this work, a discrete element model (DEM) is employed, in conjunction with the rate process theory [Kuhn MR, Mitchel JK. Modelling of soil creep with the discrete element method. Eng Computations. 1992;9(2):277–287] to simulate rock creep. The DEM numerical sample is built using a mixture of contact models between particles that combines the Flat Joint Contact Model and the Linear Model. Laboratory uniaxial compression creep tests conducted on intact slate samples are used as a benchmark to validate the methodology. Results demonstrate that, when properly calibrated, DEM models combined with the rate process theory can reproduce all creep stages observed in slate rock samples in the laboratory, including and without using constitutive models that incorporate an explicit dependence of strain rate with time. The DEM results also suggest that creep is associated to damage in the samples during the laboratory tests, due to new micro-cracks that appear when the load is applied and maintained constant at each loading stage.