ABSTRACT
An unfractured rock mass is effectively impermeable to water from engineering and hydrogeological points of view. Louis (1969) has shown that the water permeabilities of most intact rocks vary between 10−10 and 10−15 m/s. All rocks, particularly those close to the earth surface, include fractures of various sizes that provide major conducting pathways to water movement. Development of fractures due to different geological conditions such as tectonics and thermal and chemical activities in the porous or nonporous rocks changes the original strength and hydraulic properties. Many productive freshwater aquifers as well as petroleum and geothermal reservoirs are found in fractured igneous or sedimentary rocks such as sandstones and limetones. Crystalline rocks are heterogeneous and anisotropic water-bearing formations and their permeability varies markedly in short distances. Consequently, hydraulic behaviors of fractured rocks depend upon the number, extension, direction, size, aperture, and degree of connectedness of the fractures. Similarly, the amount of extractable water depends on the same features penetrated by the bore hole of the well. The existence of a connected network of fractures facilitates extraction of fluids (water, oil, and gas) from these formations by man-made structures such as vertical (well) and horizontal (gallery) shafts. Fractures play a multiple role in aquifer property alteration by changing the porosity or the permeability or both. In addition, fractured formations provide a potential underground space for nuclear waste repository siting.
