Fundamental Mechanism of Time Dependent Failure in Shale

Abstract

In underground coal mines, mining activity disturbs the natural equilibrium state of in-situ stresses. The induced and in-situ stresses deform the rockmass surrounding the mine openings. Primary roof supports impede the deformation of the rockmass overlying the entries. However, failure can occur in the bolted rockmass, causing fatalities and injuries. The rockmass failure is erratic, and its occurrence often varies from a few days to months and years after the opening of the entry. One of the often-neglected factors in this process is the effect of time on the stability of mine openings, which can often be observed in the propagation of failure in the rockmass. Coalmeasure rocks have exhibited time-dependent strength reduction in laboratory creep tests. However, the exact mechanism responsible for this time-dependent reduction in strength is not clear. Therefore, this thesis investigated the fundamental reason for macroscopic creep deformation in shale through microscopic visualization using an X-ray computed tomography (CT) technique. An approach was formulated based on the following experiments. I would also like to thank the National Institute of Occupational Safety and Health (NIOSH) for providing the necessary funding for this research. I would also like to thank the Office of Graduate Education and Life (OGEL) of WVU which in part supported this research by providing an Outstanding Merit Fellowship for Continuing Doctoral Student. I would also like to thank Dr.