Direct shear mechanism of steel fiber reinforced shotcrete-rock interface in lined hydrogen storage caverns: Insights from acoustic emission and DIC

Underground hydrogen energy storage (UHES) in lined rock caverns (LRCs) is of paramount importance in addressing the inherent instability of clean energy generation and in facilitating the accelerated restructuring of the global energy mix. However, this technology entails greater requirements for the safety and stability of concrete lining. The present study comprises a series of shear tests on steel fiber reinforced shotcrete-rock (SFC-R) specimens, which are subjected to a range of normal stress (σn), shear rate (SR), joint roughness coefficients (JRC) and steel fiber content (SF). The destabilization mechanism of the SFC-R interface is investigated through the integration of acoustic emission (AE), digital image correlation (DIC) and scanning electron microscope (SEM). Furthermore, the stress distribution characteristics of steel fibers are investigated through numerical simulation. Results show that a sudden drop in shear force occurs in the specimens after reaches the peak value, and due to the bridging effect of the steel fibers, some specimens show a rebound rise in shear force. During the shearing process, normal shear shrinkage is observed initially due to the closure of the cavity and compression of the material. Subsequently, normal shear expansion occurs due to the inhomogeneity of the joint surface. The mean level of AE hits and peak AE hits are proportional to σn, SR and JRC. Besides, they showed a positive correlation with SF only during the intensified damage stage. As σn, SR, and JRC increased, or SF decreased, the specimens demonstrated an inclination towards cracking, which ultimately resulted in the deterioration of the concrete and rock. Consequently, the stress level within the steel fibers embedded within the concrete is also increased. This is evidenced by the formation of aggregated regions exhibiting patchy deformation, as illustrated by the DIC images. •SFC-R specimens with three different natural interface morphologies and varying steel fiber content are prepared.•Direct shear tests under different normal stresses and shear rates are conducted.•AE and DIC technologies are employed to analysis the failure process and energy release pattern of the SFC-R specimens.•The stress distribution characteristics of steel fibers are investigated through numerical simulation.