An enhanced computational modelling of rock fracture-induced seismicity: the discrete element method (DEM) approach

An advancement of the discrete element method (DEM) is presented that improves simulation of seismicity in rock materials. The developed model builds on previous DEM procedures for imitating acoustic emissions and micro-seismicity in rocks. Currently, formulations that govern DEM techniques identify the breakage of inter-particle bonds and creation of cracks as a singular source of micro-seismic event. They implement a fixed criterion for clustering which fails to adequately account for the involvement of nearby particles and contacts, and does not systematically categorise the spatial, temporaland intensity characteristics of acoustic emissions and micro-seismic events. The revised DEM introduces a concept that fully recognises contributions from particles around source cracks, while integrating the motion and forces on neighbouring particles and contacts. This concept also involves the adoption of a changeable combination factor for establishing, distinguishing and recording acoustic emission/micro-seismic events. This new approach is validated against two physical laboratory experiments on Springwell sandstone and Inada granite: uniaxial and triaxial compression, and fluid injection. The distribution of acoustic emission events from the numerical model matches those visualise in physical experiments. The b_values, sizes of crack aperture and patterns of source mechanisms are also in good agreement with experimental results and, in some instances, field-scale natural conditions.