Measurement of earth pressures by means of the flat jack test

This study deals with the principle and application of a method of measuring the stresses around a rock gallery.

The measuring principle consists of cutting a drain in a gallery wall, observing the corresponding stress lessening, then restoring the initial state of stress by means of a Freyssinet flat jack. The application of this method in the Eastern iron-ore mines have given interesting results. In particular, they confirm the validity of the elastic hypothesis in these mines and enable the measurement of the stresses within them ass to be made more accurately than by the usual methods. Finally, by means of improvements, which do not unduly complicate the test performance, complete information on the elastic characteristics of the mineral may be obtained.