Discrete element modelling of rock creep behaviour using rate process theory

Abstract

Rock creep behaviour is crucial in many rock engineering projects. Different approaches have been proposed to model rock creep behaviour; however, many cannot reproduce tertiary creep (i.e., accelerating strain rates leading to rock failure). In this work, the distinct element method (DEM) is employed, in conjunction with the rate process theory (RPT) of M.R. Kuhn and J.K. Mitchell (published in 1992) 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 RPT can reproduce all creep stages observed in slate rock samples in the laboratory, including tertiary creep, without using constitutive models that incorporate an explicit dependence of strain rate on time. The DEM results also suggest that creep is associated with damage in the samples during the laboratory tests, due to new microcracks that appear when the load is applied and maintained constant at each loading stage.