Rock salt creep: a cross-check test to cover the full relevant range of deviatoric stresses

Abstract

The time-dependent response of rock salt has been mainly investigated using confined creep tests covering a differential stress range between 5 and 20 MPa. In recent years, efforts have been made to investigate the range 0.1–4.5 MPa, using dead-end drifts in underground mines to take advantage of the very stable ambient conditions (temperature, relative humidity). Up to now, the combination of experimental data in the two ranges is difficult because of the use of different salt facies, sample preparation methods, test temperatures and experimental conditions (e.g., confined vs. unconfined tests, scale of measurements). In this work, we conduct two long-term creep tests on two natural salt samples from the same origin and prepared using the same protocol. The thermo-mechanical loading path is the same for the two tests, with only a small difference in the lateral load. One test is performed in a remote drift in a salt mine and the other test is performed in a climatic chamber in the laboratory. The comparison of the results is consistent, allowing to investigate a large range of deviatoric stresses by combining results in the two facilities. The final goal of this approach is to reduce stress extrapolation by investigating the whole deviatoric range that is relevant for underground operations. Next steps include investigating in more detail the effect of intergranular fluids, testing different temperatures and performing confined tests in the mine.