A Method for Determining the Long-Term Strength of Evaporites

CIM Bulletin, 1971

A simple method is proposed for determining the longterm deformation behaviour of evaporites. The theory developed can be tested by measuring the change in diameter as a function of time of a vertical mine shaft opposite evaporite strata. Ultimate shaft closures predicted by the theory agree well with those calculated with the very much more complex theory of Serata (1968), provided that sufficiently high octahedral shear strengths are used in the fo.rmer. An analysis of measurements made in an isolated opening in a Saskatchewan potash mine shows that the octahedral shear strength of the surrounding potash and halite was approximately 500 psi several years after the opening was mined. This value is less than that determined experimentally for halite by Serata. The same data indicate, furthermore, that the in-situ octahedral shear strength is decreasing slowly with time. The current controversy regarding the actual deformation of evaporites will only be resolved by the cooperation of potash producing companies in releasing data on the long-term deformation of their mine shafts.

Keywords: Behaviours, Data, deformation, Deformations, Displacement, Evaporites, halite, Poisson's ratio, Potash Mines, R/a Octahedral Shear Strength, virgin ground, Materials, potash, Shear strength, stress