In-situ stress measurements at depth using the overcoring method at Vale's Creighton and Garson Mines

As mines are going deeper, the proper evaluation and understanding of the anticipated induced stress conditions is critical for optimal design of excavations in underground mines. Accordingly, numerical modelling programs play a key role in estimating the anticipated induced stress conditions due to various mining activities like development and stopping operations. As such, the in-situ stress data are key input parameters for carrying out numerical modelling studies to assess the impact of the induced stress state on the stability of various underground excavations. This paper will review the factors that were considered to successfully carry out in-situ stress measurements using the overcoring method at depths ranging from 1000 m to 2600 m at the Creighton and Garson Mines. Specific factors that will be discussed include but are not limited to; selection of the test site location, known geological structures and the possible influence of these on the measurements, borehole diameter, temperature control, length of test holes relative to the excavation size, and the required number of tests undertaken at each location to determine a representative result. This paper will also review some of the challenges encountered during the in-situ stress measurement program carried out at the Creighton and Garson Mines.