Forms of hydraulic fractures created during a field test in overconsolidated glacial drift

Hydraulic fractures as long as 13 m were created at depths of 2 m in overconsolidated silty clay glacial drift during a field test using equipment designed to create hydraulic fractures in oil wells. The vicinity of each fracture was excavated, typically revealing a continuous fracture whose geometry was defined by four zones: a vertical fracture adjacent to the parent borehole; a flat-lying fracture in the vicinity of the borehole; a gently dipping fracture that assumes a preferred direction of propagation away from the borehole; a vertical fracture that intersects the ground surface. The hydraulic fractures were gently dipping with a preferred direction of propagation that apparently was controlled by loading of the ground surface; the fractures propagated away from a back hoe parked next to the parent borehole. Sand pumped into some of the fractures formed permeable layers that could increase flow into or out of low-permeability soils or rock, suggesting that sand-filled hydraulic fractures could have a variety of geotechnical or environmental applications.