Dilatancy and long-term stability of deep salt caverns under cyclic loading

Abstract

Constructing salt caverns in deep formations poses significant challenges due to high geostresses, pronounced creep behavior, and particularly intense pressure fluctuations. This study first conducted mechanical experiments to investigate the long-term creep behavior of salt rock, and to examine the differences in its mechanical response under cyclic loading compared with traditional triaxial loading. The results revealed a confining-pressure-dependent nonlinear creep behavior as well as a degradation mechanism induced by cyclic loading. A numerical model was then developed that incorporate the nonlinear creep law with periodic parameter weakening. Comparative analyses of cavern dilatancy under cyclic versus constant pressure conditions were conducted, validating the necessity of integrating the periodic weakening mechanism into the numerical model. Results indicate that cyclic loading enhances the plastic deformation capacity while lowering its dilatancy threshold; For cyclic gas pressure (CGP) mode, a minimum operational pressure of 9.6 MPa is infeasible due to excessive sidewall convergence and extensive spalling risk zones, with 12 MPa recommended as the lower limit; The constant brine pressure (CBP) mode exhibits superior performance in controlling deformation and damage; For constant gas pressure (GP) mode, a constant pressure of 19.2 MPa results in no significant dilatancy damage zones in salt layer; Critically, neglecting the dynamic weakening of parameters induced by cyclic loading leads to substantial underestimation of long-term deformation, by 20.2% in this study, primarily accumulated during the unloading (gas production) phase. The findings are expected to provide valuable insights into deep salt caverns with high-pressure fluctuations.

Keywords

deep salt cavern / cyclic loading / dilatancy / cyclic gas pressure / constant brine pressure

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