A NEW FRACTURING MECHANISM FOR GRANULAR MEDIA

Borehole breakout experiments are performed on sintered glass bead bri cks and a new microscale fracturing mechanism is described that result s in a macroscopic fracture plane oriented perpendicular to the uniaxi al compressive loading stress. Scanning Electron Microscopy (SEM) is u sed to inspect the fracture surfaces and it is found that fracture pro pagation occurs through a process of grain debonding and ejection from the sample. A two-dimensional boundary integral simulation models the effect of grain removal on subsequent fracturing by reducing the Youn g's modulus of failed grains, thereby allowing the compressive loading stress to be transferred to adjoining grains and grain contacts. It i s found that this stress concentration is sufficient to induce additio nal grain failure and macroscopic fracture growth perpendicular to the applied load.