Abstract
An extensive experimental program on rock salt comprising short-term and long-term tests has been performed on samples from the same origin and prepared and preconditioned using the same protocols. The main targets are to investigate the thermo-mechanical response of rock salt under different load paths and to produce a large database on which constitutive models can be formulated and calibrated. A total of 17 tests have been conducted, including four uniaxial experiments. Temperatures range between 8 and 60 °C, and some tests last more than 2 years. The experiments cover a differential stress range relevant for underground applications. Deviators within 0.2−4.5 MPa have been investigated through uniaxial creep experiments in salt mines to take advantage of very stable ambient conditions (particularly, temperature and relative humidity). Deviators up to 35 MPa have been investigated through confined experiments in the laboratory. Additionally, a cross-check quasi-uniaxial test (confinement of 0.2 MPa) has been performed in the laboratory under conditions similar to those of the mine, and proves that experiments in both settings can be combined to extend the range of investigated stresses. However, uniaxially loaded samples show higher strain rates than confined samples. X-Ray computed tomography suggests more micro-fracturing during the former. The results obtained under confined conditions are consistent and confirm the different stress dependency of the creep rate under low and high deviators. A modified Lemaitre model is used to analyze the results. Next steps include microstructural investigations to gain insight into the dominant deformation mechanisms under different thermo-mechanical loads, allowing for more predictive constitutive models.