The RPR method for the Doorstopper technique : four or six stress components from one or two boreholes

Abstract The importance of continuosly recording strain (or displacement) recover during stress relief when conducting in situ stress measurements has been recognized by many authors as a means of assessing the quality of a measurement. This paper describes an important new use for these strain recovery curves, as four components of the stress tensor can now be obtained from one modified doorstopper stress measurement using a parameter called the recovered to peak strain invariant ratio (RPR). Modifications made to the standard doorstopper cell and to the standard field procedure are briefly described. These allow continuous recording of strain recovery while stress is being relieved, as well as the monitoring of temperature at the rock-cell interface. Then, a description of the finite element modelling allowing the production of curves relating the far field stress components in a plane parallel to the measurement plane to the stress component normal to this plane is given. Validation of the model is achieved by laboratory stress measurement simulations. Finally, comments on preliminary results of this method applied to the borehole deformation gauge stress measurement technique are made.