Behavior of a Salt Cavern When Creep Law Is Modified to Account for Low Deviatoric Stresses

Steady state creep rate of rock salt often is described through the Norton-Hoff (NH) law. Recent experimental results suggest that this law must be modified in the low deviatoric stress range. It is suggested to adopt, instead of a linear law, a step-wise linear law in the (Equation) plot, (Bilinear law, or BL). Predictions of NH and BL laws are compared in the case of an elongated cylindrical cavern submitted to a varying internal pressure when Poisson's ratio is v = 0.5. These constitutive laws do not include transient creep behavior; however, in a cavern, transient creep closure is observed; it is much longer when NH law is adopted (rather than BL law). When cavern pressure is increased abruptly after a long idle period, effective tensile stresses appear at cavern wall; they are larger and remain tensile longer when the NH model is selected. When cavern pressure is cycled, the average creep closure rate is much faster than when cavern pressure is kept constant; this is all the more true when the BL model is selected.