A Study on a Nonlinear Elastoplastic Model for Shotcrete in Sulfate Environments

Classic elastic–plastic models for concrete do not fully account for either the material properties of shotcrete or the influence of environmental factors, resulting in significant limitations in the research and application of shotcrete in tunnels. This paper comprehensively considers the early-age strength of tunnel shotcrete and the physical and chemical attack effects of a sulfate environment, to investigate the mechanical degradation mechanisms of tunnel shotcrete under sulfate conditions and establish a corresponding nonlinear elastoplastic model. This study carried out sulfate attack tests on tunnel shotcrete and systematically revealed the stress–strain evolution characteristics of shotcrete under sulfate attack. Based on experimental data on both chemical and physical attack, this paper improves the classical elastoplastic constitutive model and constructs an elastoplastic constitutive model applicable to both the early and hardening stages of shotcrete. Overall, the improved model can describe the stress–strain response of shotcrete reasonably well; however, due to the high inherent discreteness of the shotcrete material itself, some fitting deviations still exist near points of sudden change in strain or stress. Under sulfate chemical attack conditions, the cracking stress of shotcrete exhibits a nonlinear trend of first increasing and then decreasing as corrosion time progresses. Under physical attack conditions, the cracking stress shows a clear linear decrease. Furthermore, in high-concentration sulfate environments, the influence of sulfate concentration on cracking stress is moderately reduced. The results of this study provide theoretical support for the durability assessment and constitutive modeling of tunnel shotcrete in sulfate-corrosive environments.