An elastoplastic solution for lined hydrogen storage caverns during excavation and operation phases considering strain softening and dilatancy

Abstract

Underground hydrogen energy storage (UHES) in lined rock caverns (LRCs) represents a crucial solution to the challenge of unstable and uneven clean energy generation. Nevertheless, the attainment of enhanced storage efficiencies frequently necessitates the utilization of elevated hydrogen storage pressures. Consequently, a comprehensive understanding of the elastic-plastic mechanical response of surrounding rock under hydrogen pressure is of paramount importance for ensuring the safety of UHES. In this study, an elastoplastic solution of LRCs during construction and operation phases is established. Two essential phenomena affecting the post-peak mechanical responses of surrounding rock, strain softening and dilatancy, are coupled into the plastic solution. A computational process is developed and its accuracy is validated through comparison with numerical models. The influence of surrounding rock quality parameters, strain softening and dilatancy parameters, concrete quality parameters and hydrogen pressure on the radius of the plastic softening zone (R_s) and plastic residual zone (R_r) were analyzed. Results show that higher surrounding rock quality can effectively reduce both R_s and R_r. Nevertheless, when the surrounding rock quality already reaches a high standard, such as c₁ > 3.5 MPa, φ₁ > 65°, or E > 55 MPa, it becomes inefficient to overly pursue further improvements in the surrounding rock quality. Furthermore, the strain softening and dilatancy phenomena only affect R_r. Additionally, the concrete lining with higher stiffness can share a larger portion of the hydrogen pressure, thus reducing both R_s and R_r. Notably, When the elastic modulus of concrete increases from 20 MPa to 40 MPa, R_r decreases by 31.98 % and R_s decreases by 20.96 %. Moreover, the critical hydrogen pressure (P_Hcr) at which the surrounding rock begins to enter a plastic state is proportional to the ground stress (P₀). Specifically, when P₀ is increased sequentially from 2.5 MPa to 3.0 MPa and 3.5 MPa, P_Hcr sequentially becomes 2.4 MPa, 4.0 MPa, and 5.0 MPa. The findings presented in this study contribute to improving the safety of LRCs during construction and operation.