Since 1997, more than 250 hydraulic jacking tests have been conducted as part of the site investigations for different Hydro-Quebec projects in the Canadian Shield. All of these projects are located in the Grenville and Superior Geologic Province where the bedrock consists of crystalline igneous and metamorphic rocks. Hydro jacking tests serve the objective of identifying an increase in transmissivity of the rock mass with water pressure to define the upstream limit of pressure tunnel lining. A study of different test results demonstrates, for depths less than 150 m, that the tested rock masses of massive crystalline rocks behave similarly. Analysis of statistical data of minimum stress from shut-in curves and P-Q graphs are presented and compared with the leakage of a pressure tunnel in operation. It is also proposed that the ratio of initial fracture resistance to breaking and fracture reopening pressure is a parameter to consider in the analysis of results.
Since 1997, the hydraulic jacking test was added to the list of tests to be performed for Hydro-Québec projects that include the design of unlined pressure tunnels. The use of this test was extended also to projects with inclined penstocks. In most cases, the tests were conducted at shallow depths, 150m and less, except for SM-3 which is not included in the present analysis as it was at a depth of more than 250 m. Haimson & al. (1996) presents some results for this specific project. All tests were performed in crystalline rock and the number of tests conducted until the present exceeds two hundreds and fifty. The objective of this paper is first to share Hydro- Quebec's experience, from test realization to result interpretation, and also to bring out a possible typical response to hydraulic jacking of the tested crystalline rock masses.