Very slow creep tests on salt samples

¹ LMS, Ecole Polytechnique, 91128 Palaiseau Cedex, France.
² Brouard Consulting, 101 rue du Temple, 75003 Paris, France.
³ Institut de Physique du Globe de Paris, Jussieu, 75005 Paris, France.

Abstract

Long-term creep tests have been performed on rock-salt and argillite samples under very small uniaxial loadings (σ = 0.02 to 0.1 MPa) . To minimize the effects of temperature variations, testing devices were set in a mine where temperature fluctuations are of the order of one-hundredth of a degree Celsius. The mechanical loading was provided by dead weights. The deformations were measured through special displacement sensors with a resolution of ∆ε = 10^-8. Strain rates as small as έ = 7 × 10^-13s^-1 were measured. These tests allow rock-sample creep to be investigated at very small strain rates. The tests also prove that extrapolation of constitutive laws at very small rates is often incorrect.