Analytical procedure for mechanical response of surrounding rock of compressed air energy storage caverns considering bidirectional strain-softening

Rock masses exhibit significant strain-softening characteristics under high-stress conditions. During excavation, surrounding rock may undergo plastic shear failure with strain-softening. Under high internal pressure, the primary stress sequence of surrounding rock changes, leading to strain-softening in another direction, known as bidirectional strain-softening. Accordingly, an analytical method for calculating rock stress and displacement—considering the biaxial strain-softening characteristics—has been proposed from a stress path perspective. For rock masses of superior quality (e.g., Grade III and above), the effects of bidirectional strain-softening can be overlooked in the structural design calculations for caverns. However, for lower-quality rock masses (e.g., Grade V₁), the calculated rock displacements during high-pressure gas storage can differ significantly—by more than a multiple—when accounting for strain-softening versus neglecting it. For rock masses classified as Grade IV₁, this discrepancy is approximately 14%. Therefore, the strain-softening characteristics of medium-to-soft rock strata must be considered in the structural design of compressed air energy storage caverns. These findings offer valuable insights for the design of cavern structures within medium-to-soft rock formations.