Failure analysis of underground concrete silo under near-field soil explosion

The underground concrete silo is commonly constructed severing as vertical transport passages in mining and emergency exits for buried structures like tunnels, which, however, is possible to encounter accidental or intentional soil explosions (e.g., blasting excavation). The purpose of this study is to reveal the failure mode and mechanism of an underground concrete silo (46 m in height) subjected to a near-field soil explosion. The Coupled Lagrangian-Eulerian (CEL) method, along with two well-developed material models respectively for soil and concrete, is employed to handle the violent interactions between the exploded soil and the concrete silo. The numerical framework is first validated by simulations of a soil explosion beneath a concrete slab, where the predicted crack patterns of the concrete slab accord well with the experimental results. Subsequently, comprehensive numerical simulations are conducted to investigate the failure of the concrete silo under various soil explosion scenarios. The results indicate that the concrete silo experiences successively or simultaneously tensile spalling failure, local compression-induced tensile failure, and bending-induced tensile failure, with one or two predominating. The prevailing failure mode of the concrete silo is highly dependent on the intensity of the shock wave and the loading area. Further investigations expose that with the scaled distance increasing from 0.12 to 0.4 m/kg1/3, the dominant failure mode of the concrete silo transforms from local compression-induced tensile failure to overall bending-induced tensile failure. The critical scaled distance is 0.2 m/kg1/3. Regardless of the dominant failure mode, three-dimensional fracture planes that split the silo structure are generated. Besides, the tensile spalling failure, arising from the reflected tensile stress wave, is severe on the internal surface of the silo structure, consequently, fragments with velocities up to 12 m/s are produced, posing potential risks to humans and facilities inside the silo if any. This is the first time, to the authors' knowledge, the failure of the prototype of a large-scale underground concrete silo arising from a large-yield and near-field soil explosion has been investigated. The finding can benefit the research community and provide a reference for the protection of the underground concrete silo as well as the facilities inside it to withstand soil explosions.