Physical processes involved in the laboratory hydraulic fracturing of granite: Visual observations and interpretation

Most importantly, a combined effect of loading conditions and existing flaw geometries on the fracturing processes was observed. At low bridging angles, there is a distinct difference of the coalescence pattern depending on the loading condition: direct coalescence when no vertical load was applied and no coalescence when a vertical load of 5 MPa was applied. At higher bridging angles, there is no effect of the loading conditions. This is consistent with the water pressure at failure (WPmax): for higher bridging angles, WPmax is the same regardless of the loading conditions, while for lower bridging angles WPmax is larger when a vertical load of 5 MPa is applied.