Near-Surface Hydraulic Fracture

On April 30, 1999 an estimated 10,300 square meters of roof area collapsed at the Moonee Colliery longwall coal mine near Sydney, Australia. The collapse itself was not the problem; longwall coal mines are nearly always designed such that stabilization occurs through frequent caving events in the mined-out region behind the longwall face. The problem was that it occurred on a very large scale and without warning. A miner was injured when he was thrown by the resulting wind blast, and the mine was shut down contingent on mitigation of the hazard. The CSIRO Medal winning solution to this problem was to use hydraulic fracturing, applied for over 50 years for stimulating oil and gas production, to induce controlled caving of the roof rock. This development, as well as other new applications for environmental remediation and modelling the growth of magma-driven sills and laccoliths, motivated a new area of research aimed at understanding hydraulic fracture interaction with a nearby free surface. The work presented here comprises a detailed investigation into near-surface hydraulic fracture growth using analytical, numerical, and laboratory-scale experimental methods.