Computational framework for studying seismicity induced by rock engineering activities

Abstract

Rock Engineering Activities (REA), including tunneling, shaft-boring, mining, deep wastewater disposal, and geothermal energy extraction may result in unstable compressive failure of rock and unstable shear slip on pre-existing discontinuities within the affected zone. The unstable compressive failure is the violent crushing of rocks and unstable shear slip is rapid sliding on pre-existing discontinuity. Unstable failure may result in seismic events characterized by significant radiation of seismic energy. This dissertation presents a computational framework that includes methodologies, modeling approaches, and techniques for identifying the occurrence of unstable failures and estimating magnitudes of induced seismic events. The concept of failure instability, mostly developed in mining engineering, is advanced into numerical methodologies for studying seismicity in different REA. A Universal Distinct Element Code (UDEC) is used to develop the framework and exemplify its application in minimizing the intensity of potential seismic events induced by REA. For assessing the intensity of induced events, two methods are introduced for estimating radiated seismic energy: one compares the state of energy before and after an unstable failure; the other calculates energy that needs to be radiated for reaching static equilibrium. Induced seismicity in tunneling and shaft-boring settings is explored by modeling circular excavations advancing next to a normal fault in a stressed brittle rock. A single pillar supporting a tabular excavation and a strike-slip fault are modeled to study mining-induced seismicity. The application of the developed framework for studying natural earthquakes is discussed by quantifying relationships between source parameters of an earthquake rupture and then checking results against analytical solutions and globally recorded seismic data. The framework is extended to study seismicity induced by injecting fluid onto deep fault planes, a simplified analogy to wastewater disposal and geothermal energy extraction activities. Effects of injection pressure increments on the intensity of induced seismic events are analyzed to show the framework application in finding strategies to minimize seismic hazards. The calibrated framework and verified results allow for assessing potential seismicity induced by different REA in complex geological settings and adjusting design parameters to reduce the intensity of these events.