Stress measurements in soft rocks

The objective of this paper is to demonstrate that accurate and reliable in situ stress measurements can be performed in soft rocks. A quick over-view of the mechanical behaviour of soft rocks is presented. After reviewing stress measurement techniques that have been used in soft rocks, the modified doorstopper technique is presented and the advantages it has over other techniques in soft rocks are underlined. Results from laboratory simulations in controlled conditions show that the technique is reliable and accurate. It is then shown, through field applications in a potash mine in Brazil, in an underwater tunnel in shales in Canada and in an exploratory drift in molassic rocks of the French Alps, how the technique yields results that can sometimes be confirmed by field observations. (C) 2003 Elsevier Science B.V. All rights reserved.