Dry and hydraulic extensile fracturing of porous impermeable materials

Extensile hydraulic fracturing of mortar is investigated and compared to extensile dry fracturing of sandstone. The extensile fracture experiments have been performed in a Hookean cell in deformation control. The cell allows for axial loading and radial fluid pressure loading of cylindrical specimens. Variables in the experiments are the load path and the degree of saturation. In the dry fracturing tests, the sandstone specimens are sleeved. In the hydraulic fracture experiments, the mortar specimens are not sleeved so that the radial fluid pressure is free to enter the notch and the fracture once it is initiated. In the dry fracturing experiments, the sandstone becomes more ductile for increasing hydrostatic stress. In the hydraulic fracture experiments, the mortar remains brittle. The results of the hydraulic fracture experiments are very similar for the unsaturated mortar (degree of saturation 69%) and the saturated mortar (degree of saturation 100%). The saturated mortar behaves stiffer and has higher failure stresses due to the effect of pore pressures. Fracture propagation in the saturated mortar requires lower stresses, although the difference with fracture propagation in the unsaturated mortar is minor.