Transient Hydraulic Tests in Granite: Fissured Porous Medium Analysis and Results

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Abstract
Slug and pulse tests have been used extensively to measure the hydraulic conductivity and specific storage of granitic rocks. After several hundred tests using an I.G.S. design of straddle packer test equipment, it became clear that the conventional methods of test analysis were inadequate. The straddle packer equipment developed by IGS allows the time scale of a test to be altered without repositioning the packers so that a range of tests can be carried out on the same test interval. The new analysis procedure presented here uses a model of fissured rock which incorporates water movement in both the fissures and the rock matrix. A new variable is introduced which includes the parameters matrix hydraulic conductivity, matrix specific storage fissure specific storage and fissure hydraulic conductivity together with the controllable variables, effective casing radius and packer interval length. Examples of analysis using multiple tests in the same interval are presented together with the apparent relationship between measured hydraulic conductivity and specific storage. It would appear that a small number of fissures endow the rock mass with the bulk of its hydraulic conductivity and that many of the higher hydraulic conductivity tests are probably associated with localised “pipe flow”.

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