Pre-failure damage analysis for brittle rocks under triaxial compression

In this study pre-failure damage characteristics are investigated by conducting a series of conventional triaxial compression tests and corresponding numerical simulations for granite from Kirchberg (Saxony, Germany). First, lab test results are analysed. For evaluation and prediction of damage in the pre-failure range, damage indices are proposed considering increase of dissipation energy density and decrease of secant modulus. It can be concluded that the damage increases slowly before the reversal of volumetric strain and accelerates quickly afterwards. Then, a new failure criterion is deduced based on a correlation of maximum elastic strain energy density with uniaxial compressive strength and confining pressure. Finally, a micro-mechanical grain-based discrete element model using Voronoi blocks to represent minerals is set-up. It considers elastic grains and elasto-plastic contact deformations as well as inter- and intra-granular fracturing. The triaxial compression tests are simulated and the damage process including evolution of damage indices are investigated in detail. The proposed approaches can be used to predict and analyse limit and damage state of brittle rocks.