Very Slow Creep Tests on Salt Samples
Abstract
The objective of this paper is to assess the creep law of natural salt in a small deviatoric stress range. In this range, creep is suspected to be much faster than what is predicted by most constitutive laws used in the cavern and mining industries. Five 2-year, multistage creep tests were performed with creep-testing devices set in a gallery of the Altaussee mine in Austria to take advantage of the very stable temperature and humidity conditions in this salt mine. Each stage was 8-month long. Dead loads were applied, and vertical displacements were measured through gages that had a resolution of 12.5 nm. Loading steps were 0.2, 0.4, and 0.6 MPa, which are much smaller than the loads that are usually applied during creep tests (5-20 MPa). Five salt samples were used: two samples were cored from the Avery Island salt mine in Louisiana, United States; two samples were cored from the Gorleben salt mine in Germany; and one sample was cored from a deep borehole at Hauterives in Drôme, France. During these tests, transient creep is relatively long (6-10 months). Measured steady-state strain rates (\dot {ɛ } = 10-13-10-12 s-1) are much faster (by 7-8 orders of magnitude) than those extrapolated from relatively high-stress tests ( σ = 5-20 MPa). When compared to n = 5 within the high-stress domain for Gorleben and Avery Island salts, a power-law stress exponent within the low-stress domain appears to be close to n = 1. These results suggest that the pressure solution may be the dominant deformation mechanism in the steady-state regime reached by the tested samples and will have important consequences for the computation of caverns or mines behavior. This project was funded by the Solution-Mining Research Institute.
- Publication:
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Rock Mechanics and Rock Engineering
- Pub Date:
- September 2019
- DOI:
- 10.1007/s00603-019-01778-9
- Bibcode:
- 2019RMRE...52.2917B
- Keywords:
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- Salt creep;
- Slow creep rate;
- Pressure solution;
- Dislocation creep