This study aims to investigate the failure mechanism of rock fractures induced by excavation unloading and fluid injection in Singapore Bukit Timah granite. The experimental tests on unloading-induced and injection-induced fracture instability are conducted based on the shear-flow experiments. The tests on unloading-induced fracture instability consist of three groups of experiments: the influences of initial normal stress, shear stress level, and unloading rate. The result shows that reducing initial normal stress, shear stress level and unloading rate slowly can help to prevent the unloading-induced fracture instability. The tests on injection-induced fracture instability consider the effect of fluid overpressure and show that the mechanism of injection-induced fracture instability is similar to the mechanism of unloading-induced fracture instability. The results obtained from both experiments indicate that the mechanism of induced seismicity can be interpreted by the Mohr–Coulomb failure criterion through different approaches of moving and modifying the Mohr circle approaching the failure envelope.

Master of Science (Civil Engineering)