Modelling Brittle Failure Of Sandstone At Laboratory And Field Scale Using The Bonded Block Method

The bonded block method is a subtype of the discrete element method where intact rock can be represented using an assembly of 2D polygons or 3D polyhedra with strong, stiff contacts. Brittle fracture can be simulated by shear or tension failure of bonded contacts. This paper presents results from a series of 3D bonded block models based on sandstone from the Snapper Point formation in NSW. First, a series of laboratory scale compression and tension tests are used to develop calibrated contact micro parameters that broadly reproduce laboratory index properties and macroscopic brittle fracture behaviour. Next, the calibrated parameters are used as inputs for a field scale bonded block model of a deep shaft in massive sandstone with high horizontal in situ stress. The shaft model explores the potential for notch breakout by progressive brittle spalling. Compared with results from a continuum analysis, the bonded block model produces a more explicit representation of progressive damage and the transition from an intact continuum to fractured discontinuum. Fracture initiation, propagation, and coalescence can be directly observed by tracking shear and tensile failure of bonded contacts. The results demonstrate that the bonded block method can be a useful tool to characterise rock mass yielding and post-peak strength for problems where brittle fracture controls stability.