Improvement in the interpretation of stress measurements by use of the overcoring method: development of a new approach

Determination of the state of the initial stresses in a rock formation is still one of the most important and complex problems in geotechnics. The over-coring method of measuring the stresses is one of the measurement methods most frequently used in geotechnics. It has been shown to be highly suitable for measuring the stresses in “hard and sound” rocks. However, applied to rocks which have a partialy elastic behaviour the method comes up against many problems the biggest of which are: (1) the non-elastic behaviour of the rock; and (2) the presence of natural fractures or those caused by the overcoring operation. These problems make it impossible to obtain correct deformation measurements which can be interpreted in terms of stresses. To overcome these problems, a new method has been developed based on the use of the deformations recorded at the start of the overcoring tests this method is the subject of the present article.